| 1. |
- Andersson, Charlotta S., et al.
(författare)
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The Mycobacterium tuberculosis Very-Long-Chain Fatty Acyl-CoA Synthetase : Structural Basis for Housing Lipid Substrates Longer than the Enzyme
- 2012
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Ingår i: Structure. - : Elsevier BV. - 0969-2126 .- 1878-4186. ; 20:6, s. 1062-1070
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Tidskriftsartikel (refereegranskat)abstract
- The Mycobacterium tuberculosis acid-induced operon MymA encodes the fatty acyl-CoA synthetase FadD13 and is essential for virulence and intracellular growth of the pathogen. Fatty acyl-CoA synthetases activate lipids before entering into the metabolic pathways and are also involved in transmembrane lipid transport. Unlike soluble fatty acyl-CoA synthetases, but like the mammalian integral-membrane very-long-chain acyl-CoA synthetases, FadD13 accepts lipid substrates up to the maximum length tested (C-26). Here, we show that FadD13 is a peripheral membrane protein. The structure and mutational studies reveal an arginine- and aromatic-rich surface patch as the site for membrane interaction. The protein accommodates a hydrophobic tunnel that extends from the active site toward the positive patch and is sealed by an arginine-rich lid-loop at the protein surface. Based on this and previous data, we propose a structural basis for accommodation of lipid substrates longer than the enzyme and transmembrane lipid transport by vectorial CoA-esterification.
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| 2. |
- Ariöz, Candan, 1983-, et al.
(författare)
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Anionic Lipid Binding to the Foreign Protein MGS Provides a Tight Coupling between Phospholipid Synthesis and Protein Overexpression in Escherichia coli
- 2013
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 52:33, s. 5533-5544
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Tidskriftsartikel (refereegranskat)abstract
- Certain membrane proteins involved in lipid synthesis can induce formation of new intracellular membranes in Escherichia coli, i.e., intracellular vesicles. Among those, the foreign monotopic glycosyltransferase MGS from Acholeplasma laidlawii triggers such massive lipid synthesis when overexpressed. To examine the mechanism behind the increased lipid synthesis, we investigated the lipid binding properties of MGS in vivo together with the correlation between lipid synthesis and MGS overexpression levels. A good correlation between produced lipid quantities and overexpressed MGS protein was observed when standard LB medium was supplemented with four different lipid precursors that have significant roles in the lipid biosynthesis pathway. Interestingly, this correlation was highest concerning anionic lipid production and at the same time dependent on the selective binding of anionic lipid molecules by MGS. A selective interaction with anionic lipids was also observed in vitro by P-31 NMR binding studies using bicelles prepared with E. coli lipids. The results clearly demonstrate that the discriminative withdrawal of anionic lipids, especially phosphatidylglycerol, from the membrane through MGS binding triggers an in vivo signal for cells to create a feed-forward stimulation of lipid synthesis in E. coil. By this mechanism, cells can produce more membrane surface in order to accommodate excessively produced MGS molecules, which results in an interdependent cycle of lipid and MGS protein synthesis.
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| 3. |
- Ariöz, Candan, 1983-
(författare)
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Exploring the Interplay of Lipids and Membrane Proteins
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interplay between lipids and membrane proteins is known to affect membrane protein topology and thus have significant effect (control) on their functions. In this PhD thesis, the influence of lipids on the membrane protein function was studied using three different membrane protein models.A monotopic membrane protein, monoglucosyldiacylglyecerol synthase (MGS) from Acholeplasma laidlawii is known to induce intracellular vesicles when expressed in Escherichia coli. The mechanism leading to this unusual phenomenon was investigated by various biochemical and biophysical techniques. The results indicated a doubling of lipid synthesis in the cell, which was triggered by the selective binding of MGS to anionic lipids. Multivariate data analysis revealed a good correlation with MGS production. Furthermore, preferential anionic lipid sequestering by MGS was shown to induce a different fatty acid modeling of E. coli membranes. The roles of specific lipid binding and the probable mechanism leading to intracellular vesicle formation were also investigated.As a second model, a MGS homolog from Synechocystis sp. PCC6803 was selected. MgdA is an integral membrane protein with multiple transmembrane helices and a unique membrane topology. The influence of different type of lipids on MgdA activity was tested with different membrane fractions of Synechocystis. Results indicated a very distinct profile compared to Acholeplasma laidlawii MGS. SQDG, an anionic lipid was found to be the species of the membrane that increased the MgdA activity 7-fold whereas two other lipids (PG and PE) had only minor effects on MgdA. Additionally, a working model of MgdA for the biosynthesis and flow of sugar lipids between Synechocystis membranes was proposed.The last model system was another integral membrane protein with a distinct structure but also a different function. The envelope stress sensor, CpxA and its interaction with E. coli membranes were studied. CpxA autophosphorylation activity was found to be positively regulated by phosphatidylethanolamine and negatively by anionic lipids. In contrast, phosphorylation of CpxR by CpxA revealed to be increased with PG but inhibited by CL. Non-bilayer lipids had a negative impact on CpxA phosphotransfer activity.Taken together, these studies provide a better understanding of the significance of the interplay of lipids and model membrane proteins discussed here.
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| 4. |
- Ariöz, Candan, 1983-, et al.
(författare)
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Heterologous overexpression of a monotopic glucosyltransferase (MGS) induces fatty acid remodeling in Escherichia coli membranes :
- 2014
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1838:7, s. 1862-1870
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Tidskriftsartikel (refereegranskat)abstract
- The membrane protein monoglucosyldiacylglycerol synthase (MGS) from Acholeplasma laidlawii is responsible for the creation of intracellular membranes when overexpressed in Escherichia coli (E. coli). The present study investigates time dependent changes in composition and properties of E. coli membranes during 22 h of MGS induction. The lipid/protein ratio increased by 38% in MGS-expressing cells compared to control cells. Time-dependent screening of lipids during this period indicated differences in fatty acid modeling. (1) Unsaturation levels remained constant for MGS cells (~ 62%) but significantly decreased in control cells (from 61% to 36%). (2) Cyclopropanated fatty acid content was lower in MGS producing cells while control cells had an increased cyclopropanation activity. Among all lipids, phosphatidylethanolamine (PE) was detected to be the most affected species in terms of cyclopropanation. Higher levels of unsaturation, lowered cyclopropanation levels and decreased transcription of the gene for cyclopropane fatty acid synthase (CFA) all indicate the tendency of the MGS protein to force E. coli membranes to alter its usual fatty acid composition.
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| 5. |
- Bakali, Amin, et al.
(författare)
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Crystal structure of YegS, a homologue to the mammalian diacylglycerol kinases, reveals a novel regulatory metal binding site
- 2007
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 282:27, s. 19644-19652
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Tidskriftsartikel (refereegranskat)abstract
- The human lipid kinase family controls cell proliferation, differentiation, and tumorigenesis and includes diacylglycerol kinases, sphingosine kinases, and ceramide kinases. YegS is an Escherichia coli protein with significant sequence homology to the catalytic domain of the human lipid kinases. We have solved the crystal structure of YegS and shown that it is a lipid kinase with phosphatidylglycerol kinase activity. The crystal structure reveals a two-domain protein with significant structural similarity to a family of NAD kinases. The active site is located in the interdomain cleft formed by four conserved sequence motifs. Surprisingly, the structure reveals a novel metal binding site composed of residues conserved in most lipid kinases.
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| 6. |
- Berg, Stefan, et al.
(författare)
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Sequence properties of the 1,2-diacylglycerol 3-glucosyltransferase from Acholeplasma laidlawii membranes : Recognition of a large group of lipid glycosyltransferases in eubacteria and archaea
- 2001
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:25, s. 22056-22063
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of the nonbilayer-prone α-monoglucosyldiacylglycerol (MGlcDAG) is crucial for bilayer packing properties and the lipid surface charge density in the membrane ofAcholeplasma laidlawii. The gene for the responsible, membrane-bound glucosyltransferase (alMGS) (EC 2.4.1.157) was sequenced and functionally cloned in Escherichia coli, yielding MGlcDAG in the recombinants. Similar amino acid sequences were encoded in the genomes of several Gram-positive bacteria (especially pathogens), thermophiles, archaea, and a few eukaryotes. All of these contained the typical EX7E catalytic motif of the CAZy family 4 of α-glycosyltransferases. The synthesis of MGlcDAG by a close sequence analog from Streptococcus pneumoniae (spMGS) was verified by polymerase chain reaction cloning, corroborating a connection between sequence and functional similarity for these proteins. However, alMGS and spMGS varied in dependence on anionic phospholipid activators phosphatidylglycerol and cardiolipin, suggesting certain regulatory differences. Fold predictions strongly indicated a similarity for alMGS (and spMGS) with the two-domain structure of the E. coli MurG cell envelope glycosyltransferase and several amphipathic membrane-binding segments in various proteins. On the basis of this structure, the alMGS sequence charge distribution, and anionic phospholipid dependence, a model for the bilayer surface binding and activity is proposed for this regulatory enzyme.
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| 7. |
- Edman, Maria, et al.
(författare)
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Structural features of glycosyltransferases synthesizing major bilayer and nonbilayer-prone membrane lipids in Acholeplasma laidlawii and Streptococcus pneumoniae
- 2003
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 278:10, s. 8420-8428
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Tidskriftsartikel (refereegranskat)abstract
- In membranes of Acholeplasma laidlawii two consecutively acting glucosyltransferases, the (i) alpha-monoglucosyl-diacylglycerol. (MGlcDAG) synthase (aIMGS) (EC 2.4.1.157) and the (ii) alpha-diglucosyl-DAG (DGlcDAG) synthase (alDGS) (EC 2.4.1.208), are involved in maintaining (i) a certain anionic lipid surface charge density and (ii) constant nonbilayer/bilayer conditions (curvature packing stress), respectively. Cloning of the aIDGS gene revealed related uncharacterized sequence analogs especially in several Gram-positive pathogens, thermophiles and archaea, where the encoded enzyme function of a potential Streptococcus pneumoniae DGS gene (cpoA) was verified. A strong stimulation of aIDGS by phosphatidylglycerol (PG), cardiolipin, or nonbilayer-prone 1,3-DAG was observed, while only PG stimulated CpoA. Several secondary structure prediction and fold recognition methods were used together with SWISS-MODEL to build three-dimensional model structures for three MGS and two DGS lipid glycosyltransferases. Two Escherichia coli proteins with known structures were identified as the best templates, the membrane surface-associated two-domain glycosyltransferase MurG and the soluble GlcNAc epimerase. Differences in electrostatic surface potential between the different models and their individual domains suggest that electrostatic interactions play a role for the association to membranes. Further support for this was obtained when hybrids of the N- and C-domain, and full size alMGS with green fluorescent protein were localized to different regions of the E. coli inner membrane and cytoplasm in vivo. In conclusion, it is proposed that the varying abilities to bind, and sense lipid charge and curvature stress, are governed by typical differences in charge (pI values), amphiphilicity, and hydrophobicity for the N- and (catalytic) C-domains of these structurally similar membrane-associated enzymes.
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| 8. |
- Eriksson, Hanna M., 1978-, et al.
(författare)
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High-yield expression and purification of a monotopic membrane glycosyltransferase
- 2009
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Ingår i: Protein Expression and Purification. - : Elsevier. - 1046-5928 .- 1096-0279. ; 66:2, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Membrane proteins are essential to many cellular processes. However, the systematic study of membrane protein structure has been hindered by the difficulty in obtaining large quantities of these proteins. Protein overexpression using Escherichia coli is commonly used to produce large quantities of protein, but usually yields very little membrane protein. Furthermore, optimization of the expressing conditions, as well as the choice of detergent and other buffer components, is thought to be crucial for increasing the yield of stable and homogeneous protein. Herein we report high-yield expression and purification of a membrane-associated monotopic protein, the glycosyltransferase monoglucosyldiacylglycerol synthase (alMGS), in E. coli. Systematic optimization of protein expression was achieved through controlling a few basic expression parameters, including temperature and growth media, and the purifications were monitored using a fast and efficient size-exclusion chromatography (SEC) screening method. The latter method was shown to be a powerful tool for fast screening and for finding the optimal protein-stabilizing conditions. For alMGS it was found that the concentration of detergent was just as important as the type of detergent, and a low concentration of n-Dodecyl-β-D-maltoside (DDM) (~1× critical micelle concentration) was the best for keeping the protein stable and homogeneous. By using these simply methods to optimize the conditions for alMGS expression and purification, the final expression level increase by two orders of magnitude, reaching 170 mg of pure protein per litre culture.
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| 9. |
- Eriksson, Hanna M., 1978-, et al.
(författare)
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Increased amounts of overexpressed membrane proteins in Escherichia coli by co-expression with a foreign vesicle-inducing protein
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Escherichia coli has a limited capacity to overexpress integral membrane proteins to amounts needed for structural studies. This is usually attributed to the limited capacity of the Sec transport machinery, shortage of accessory chaperons, sub-optimal codon usage, potentially “wrong” lipids, and lack of membrane space for the new proteins. A foreign, monotopic lipid glycosyltransferase was recently shown to induce the formation of extensive amounts of intracellular vesicles in E. coli. We show here that such vesicles can improve the expressed levels up to 3-4 times for a substantial fraction of integral membrane proteins tested. These had 2 to 12 transmembrane helices, and all had a C-terminally fused GFP reporter. Strongly overexpressed proteins yielded intensely green vesicles, of slightly lower buoyant density than the inner membranes. Most proteins could be detected in the vesicles. Multivariate sequence analyses indicated a correlation between sequence property features and expression levels, and factors analyzed involved protein mass, transmembrane segments, inside/outside loops, etc. It is concluded that this vesicular system can yield substantial improvements in expression levels, by creation of extra membranes and lateral space in E. coli.
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| 10. |
- Eriksson, Hanna M., 1987-
(författare)
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Intracellular vesicles induced by monotopic membrane protein in Escherichia coli
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The monotopic membrane protein alMGS, a glycosyltransferase catalyzing glucolipid synthesis in Acholeplasma laidlawii, was overexpressed in Escherichia coli. Optimization of basic growth parameters was performed, and a novel method for detergent and buffer screening using a small size-exclusion chromatography was developed. This resulted in a tremendous increase in protein yields, as well as the unexpected discovery that the protein induces intracellular vesicle formation in E. coli. This was confirmed by sucrose density separation and Cryo-TEM of membranes, and the properties of the vesicles were analyzed using SDS-PAGE, western blot and lipid composition analysis. It is concluded that both alMGS and alDGS, the next enzyme in glucolipid pathway, have the ability to make the membrane bend and eventually form vesicles. This is likely due to structural and electrostatic properties, such as the way the proteins penetrate the membrane interface and thereby expand one monolayer. The highly positively charged binding surfaces of the glycosyltransferases may bind negatively charged lipids, such as Phosphatidylglycerol (PG), in the membrane and withdraw it from the general pool of lipids. This would increase the overall lipid synthesis, since PG is a pace-keeper, and the local concentration of nonbilayer prone lipids, such as Phosphatidylethanolamine, can increase and also induce bending of the membrane. The formation of surplus membrane inside the E. coli cell was used to develop a generic method for overexpression of membrane proteins. A proof-of-principle experiment with a test set of twenty membrane proteins from E. coli resulted in elevated expression levels for about half of the set. Thus, we believe that this method will be a useful tool for overexpression of many membrane proteins. By engineering E. coli mutants with different lipid compositions, fine-tuning membrane properties for different proteins is also possible.
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| 11. |
- Erixon, Martin, et al.
(författare)
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3,4-dge in peritoneal dialysis fluids cannot be found in plasma after infusion into the peritoneal cavity.
- 2008
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Ingår i: Peritoneal Dialysis International. - 1718-4304. ; 28:3, s. 277-282
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Glucose degradation products (GDPs) are important in the outcome of peritoneal dialysis (PD) treatment. 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic GDP found in conventionally manufactured fluids and may, in addition, be recruited from 3-deoxyglucosone (3-DG). It is not known what happens with those GDPs in patients during PD. The aim of this study was to investigate if the 3,4-DGE and 3-DG in PD fluids can be found in plasma during treatment. DESIGN: PD patients were dialyzed with a conventional PD fluid containing 43 mumol/L 3,4-DGE and 281 mumol/L 3-DG. Parallel experiments were performed in rats as well as in vitro with human plasma. The rats were dialyzed with a PD fluid containing 100 mumol/L 3,4-DGE and 200 mumol/L 3-DG. RESULTS: The concentration of 3,4-DGE in the peritoneum decreased at a much higher rate than 3-DG during the dwell. 3,4-DGE was not, however, detected in the plasma of patients or rats during dialysis. The concentration of 3-DG in plasma peaked shortly after infusion of the fluid to the peritoneal cavity. The concentration of 3,4-DGE during experimental incubation in plasma decreased rapidly, while the concentration of 3-DG decreased only 10% as rapidly or less. CONCLUSION: 3,4-DGE could not be detected in plasma from either PD patients or rats during dialysis. This is presumably due to its high reactivity. 3-DG may, on the other hand, pass through the membrane and be detected in the blood.
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| 12. |
- Erixon, Martin, et al.
(författare)
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3,4-dideoxyglucosone-3-ene in peritoneal dialysis fluids infused into the peritoneal cavity cannot be found in plasma.
- 2009
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Ingår i: Peritoneal Dialysis International. - 1718-4304. ; 29 Suppl 2, s. 28-31
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Glucose degradation products (GDPs) are important for the outcome of peritoneal dialysis (PD) treatment. The most cytotoxic GDP found in conventionally manufactured fluids, 3,4-dideoxyglucosone-3-ene (3,4-DGE), may in addition be recruited from 3-deoxyglucosone (3-DG). What happens with the GDPs in the fluid infused into patients during PD is not known. We investigated whether 3,4-DGE and 3-DG in PD fluid can be found in plasma during treatment. DESIGN: Patients on PD were dialyzed with a conventional PD fluid containing 43 micromol/L 3,4-DGE and 281 micromol/L 3-DG. Parallel experiments were performed in rats and in vitro with human plasma. The rats were dialyzed with a PD fluid containing 100 micromol/L 3,4-DGE and 200 micromol/L 3-DG. RESULTS: The 3,4-DGE concentration in the peritoneum declined at a much higher rate during the dwell than did the 3-DG concentration. However, 3,4-DGE was not detected in the plasma of patients or of rats during dialysis. The 3-DG concentration in plasma peaked shortly after infusion of fluid into the peritoneal cavity. The 3,4-DGE concentration during experimental incubation in plasma declined rapidly; the 3-DG concentration declined only 10% as rapidly (or less). CONCLUSION: During dialysis, 3,4-DGE could not be detected in plasma of either PD patients or rats, presumably because of its high reactivity. On the other hand, 3-DG may pass through the membrane and be detected in the blood.
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| 13. |
- Erixon, Martin, et al.
(författare)
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How to avoid glucose degradation products in peritoneal dialysis fluids
- 2006
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Ingår i: Peritoneal Dialysis International. - 1718-4304. ; 26:4, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The formation of glucose degradation products (GDPs) during sterilization of peritoneal dialysis fluids (PDFs) is one of the most important aspects of biocompatibility of glucose-containing PDFs. Producers of PDFs are thus trying to minimize the level of GDPs in their products. 3,4-Dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP in PDFs. It exists in a temperature-dependent equilibrium with a pool of 3-deoxyglucosone (3-DG) and is a precursor in the irreversible formation of 5-hydroxymethyl furaldehyde (5-HMF). The aim of the present study was to investigate how to minimize GDPs in PDFs and how different manufacturers have succeeded in doing so. Design: Glucose solutions at different pHs and concentrations were heat sterilized and 3-DG, 3,4-DGE, 5-HMF, formaldehyde, and acetaldehyde were analyzed. Conventional as well as biocompatible fluids from different manufacturers were analyzed in parallel for GDP concentrations. Results: The concentrations of 3-DG and 3,4-DGE produced during heat sterilization decreased when pH was reduced to about 2. Concentration of 5-HMF decreased when pH was reduced to 2.6. After further decrease to a pH of 2.0, concentration of 5-HMF increased slightly, and below a pH of 2.0 it increased considerably, together with formaldehyde; 3-DG continued to drop and 3,4-DGE remained constant. Inhibition of cell growth was paralleled by 3,4-DGE concentration at pH 2.0-6.0. A high glucose concentration lowered concentrations of 3,4-DGE and 3-DG at pH 5.5 and of 5-HMF at pH 1. At pH 2.2 and 3.2, glucose concentration had a minor effect on the formation of GDPs. All conventional PDFs contained high levels of 3,4-DGE and 3-DG. Concentrations were considerably lower in the biocompatible fluids. However, the concentration of 5-HMF was slightly higher in all the biocompatible fluids. Conclusion: The best way to avoid reactive GDPs is to have a pH between 2.0 and 2.6 during sterilization. If pHs outside this range are used, it becomes more important to have There are large variations in GDPs, both within and between biocompatible and conventionally manufactured PDFs.
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| 14. |
- Erixon, Martin, et al.
(författare)
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PD fluids contain high concentrations of cytotoxic GDPs directly after sterilization
- 2004
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Ingår i: Peritoneal Dialysis International. - 1718-4304. ; 24:4, s. 392-398
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Glucose degradation products (GDPs) in peritoneal dialysis (PD) fluids are cytotoxic and affect the survival of the peritoneal membrane. One of the most reactive GDPs in PD fluids is 3,4-dideoxyglucosone-3-ene (3,4-DGE). 3,4-DGE has been reported as an intermediate between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl furaldehyde (5-HMF) during degradation of glucose. In PD fluids, 3,4-DGE exists in a temperature-dependent equilibrium with a pool of unidentified substances. The aim of this study was to explore this equilibrium and its temperature dependence during the first months of storage after the sterilization procedure. Methods: GDPs and inhibition of cell growth (ICG) were measured directly after sterilization of the PD fluid and during storage at different temperatures for 60 days. The following GDPs were analyzed: 3-DG, 3,4-DGE, 5-HMF, formaldehyde, acetaldehyde, glyoxal, and methylglyoxal. Results: Immediately after sterilization, the concentration of 3,4-DGE was 125 mumol/L. During the first weeks of storage, it decreased by about 80%. At the same time, the 3-DG concentration increased. None of the other GDPs were significantly affected. Cytotoxicity correlated well with the concentration of 3,4-DGE. When pure 3,4-DGE was substituted for the lost amount of 3,4-DGE after 30 days of storage, the initial ICG was almost completely regained. Conclusions: Heat sterilization of PD fluids promotes the formation of large quantities of 3,4-DGE, rendering the fluid highly cytotoxic. During storage, the main part of 3,4-DGE is reversibly converted in a temperature-dependent manner to a less cytotoxic pool, consisting mainly of 3-DG. Cytotoxicity seems to be dependent exclusively on 3,4-DGE. In order to avoid higher levels of 3,4-DGE concentrations, PD fluids should not be used too soon after sterilization and should not be stored at temperatures above room temperature.
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| 15. |
- Erixon, Martin, et al.
(författare)
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Take care in how you store your PD fluids: Actual temperature determines the balance between reactive and non-reactive GDPs
- 2005
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Ingår i: Peritoneal Dialysis International. - 1718-4304. ; 25:6, s. 583-590
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Tidskriftsartikel (refereegranskat)abstract
- Objective: During heat sterilization and during prolonged storage, glucose in peritoneal dialysis fluids (PDF) degrades to carbonyl compounds commonly known as glucose degradation products (GDPs). Of these, 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic. It is an intermediate in degradation between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl-2-furaldehyde (5-HMF). We have earlier reported that there seems to be equilibrium between these GDPs in PDF. The aim of the present study was to investigate details of this equilibrium. Methods: Aqueous solutions of pure 3-DG, 3,4-DGE, and 5-HMF were incubated at 40 degrees C for 40 days., Conventional and low-GDP fluids were incubated at various temperatures for up to, 3 weeks. Formaldehyde, acetaldehyde, glyoxal, methylglyoxal, 3-DG, 3,4-DGE, and 5-HMF were analyzed using high performance liquid chromatography. Results: Incubation of 100 mu mol/L 3,4-DGE resulted in the production of 36 mu mol/L 3-DG, 4 mu mol/L 5-HMF, and 40 mu mol/L unidentified substances. With the same incubation, 200 mu mol/L 3-DG was converted to 9 mu mol/L 3,4-DGE, 6 mu mol/L 5-HMF, and 14 mu mol/L unidentified substances. By contrast, 100 mu mol/L 5-HMF was uninfluenced by incubation. In a conventional PDF incubated at 60 degrees C for 1 day, the 3,4-DGE concentration increased from 14 to a maximum of 49 mu mol/L. When the fluids were returned to room temperature, the concentration decreased but did not reach original values until after 40 days. In a low GDP fluid, 3,4-DGE increased and decreased in the same manner as in the conventional fluid but reached a maximum of only 0.8 mu moL/L. Conclusions: Considerable amounts of 3,4-DGE maybe recruited by increases in temperature in conventional PDFs. Lowering the temperature will again reduce the concentration but much more time will be needed. Precursors for 3,4-DGE recruitment are most probably 3-DG and the enol 3-deoxyaldose-2-ene, but not 5-HMF. Considering the ease at which 3,4-DGE is recruited from its pool of precursors and the difficulty of getting rid of it again, one should be extremely careful with the temperatures conventional PDFs are exposed to.
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| 16. |
- Ge, Changrong, et al.
(författare)
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Import Determinants of Organelle-Specific and Dual Targeting Peptides of Mitochondria and Chloroplasts in Arabidopsis thaliana
- 2014
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Ingår i: Molecular Plant. - : Elsevier BV. - 1674-2052 .- 1752-9867. ; 7:1, s. 121-136
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Tidskriftsartikel (refereegranskat)abstract
- Most of the mitochondrial and chloroplastic proteins are synthesized in the cytosol as precursor proteins carrying an N-terminal targeting peptide (TP) directing them specifically to a correct organelle. However, there is a group of proteins that are dually targeted to mitochondria and chloroplasts using an ambiguous N-terminal dual targeting peptide (dTP). Here, we have investigated pattern properties of import determinants of organelle-specific TPs and dTPs combining mathematical multivariate data analysis (MVDA) with in vitro organellar import studies. We have used large datasets of mitochondrial and chloroplastic proteins found in organellar proteomes as well as manually selected data sets of experimentally confirmed organelle-specific TPs and dTPs from Arabidopsis thaliana. Two classes of organelle-specific TPs could be distinguished by MVDA and potential patterns or periodicity in the amino acid sequence contributing to the separation were revealed. dTPs were found to have intermediate sequence features between the organelle-specific TPs. Interestingly, introducing positively charged residues to the dTPs showed clustering towards the mitochondrial TPs in silico and resulted in inhibition of chloroplast, but not mitochondrial import in in vitro organellar import studies. These findings suggest that positive charges in the N-terminal region of TPs may function as an 'avoidance signal' for the chloroplast import.
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| 17. |
- Ge, Changrong, et al.
(författare)
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Membrane remodeling capacity of a vesicle-inducing glycosyltransferase
- 2014
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 281:16, s. 3667-3684
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular vesicles are abundant in eukaryotic cells but absent in the Gram-negative bacterium Escherichia coli. However, strong overexpression of a monotopic glycolipid-synthesizing enzyme, monoglucosyldiacylglycerol synthase from Acholeplasma laidlawii (alMGS), leads to massive formation of vesicles in the cytoplasm of E. coli. More importantly, alMGS provides a model system for the regulation of membrane properties by membrane-bound enzymes, which is critical for maintaining cellular integrity. Both phenomena depend on how alMGS binds to cell membranes, which is not well understood. Here, we carry out a comprehensive investigation of the membrane binding of alMGS by combining bioinformatics methods with extensive biochemical studies, structural modeling and molecular dynamics simulations. We find that alMGS binds to the membrane in a fairly upright manner, mainly by residues in the N-terminal domain, and in a way that induces local enrichment of anionic lipids and a local curvature deformation. Furthermore, several alMGS variants resulting from substitution of residues in the membrane anchoring segment are still able to generate vesicles, regardless of enzymatic activity. These results clarify earlier theories about the driving forces for vesicle formation, and shed new light on the membrane binding properties and enzymatic mechanism of alMGS and related monotopic GT-B fold glycosyltransferases.
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| 18. |
- Ge, Changrong, 1980-, et al.
(författare)
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Modulation of Escherichia coli Cell Membrane by a Monotopic Lipid Glycosyltransferase - an Exploration of Potential Mechanisms
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Intracellular vesicles are abundant in eukaryotic cells but are rare in Gram-negative bacterium Escherichia coli. Strongly overexpression of a monotopic glycolipid-synthesizing enzyme could induce massive formation of “foreign” vesicles in the cytoplasm. Here we investigate how this membrane-associated enzyme is able to bend and deform the plasma membrane. Limited proteolysis combined with ESI-MS suggested interface binding is mediated through both its two Rossmann fold topological domains. Detailed subcellular localization and liposome binding assay indicates different interface anchoring regions in the protein, and anionic lipid seems to influence the binding properties of the anchoring segments. Genetic engineering of a known membrane-bound segment to explore its vesiculation potentials led to the identification of important catalytic residues (regions). Flow cytometry and infrared spectroscopy were also performed on bacterial cells to get more insight into the cellular morphology and internal complexity. The linking region between two domains was demonstrated to be crucial for both catalytic function and vesiculation capacity of the enzyme. Based on our findings, we propose, that scaffold-like structural feature of this enzyme is most likey one of key elements contributing to vesiculation.
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| 19. |
- Ge, Changrong, 1980-
(författare)
-
Property-controlling Enzymes at the Membrane Interface
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Monotopic proteins represent a specialized group of membrane proteins in that they are engaged in biochemical events taking place at the membrane interface. In particular, the monotopic lipid-synthesizing enzymes are able to synthesize amphiphilic lipid products by catalyzing two biochemically distinct molecules (substrates) at the membrane interface. Thus, from an evolutionary point of view, anchoring into the membrane interface enables monotopic enzymes to confer sensitivity to a changing environment by regulating their activities in the lipid biosynthetic pathways in order to maintain a certain membrane homeostasis. We are focused on a plant lipid-synthesizing enzyme DGD2 involved in phosphate shortage stress, and analyzed the potentially important lipid anchoring segments of it, by a set of biochemical and biophysical approaches. A mechanism was proposed to explain how DGD2 adjusts its activity to maintain a proper membrane. In addition, a multivariate-based bioinformatics approach was used to predict the lipid-binding segments for GT-B fold monotopic enzymes. In contrast, a soluble protein Myr1 from yeast, implicated in vesicular traffic, was also proposed to be a membrane stress sensor as it is able to exert different binding properties to stressed membranes, which is probably due to the presence of strongly plus-charged clusters in the protein. Moreover, a bacterial monotopic enzyme MGS was found to be able to induce massive amounts of intracellular vesicles in Escherichia coli cells. The mechanisms involve several steps: binding, bilayer lateral expansion, stimulation of lipid synthesis, and membrane bending. Proteolytic and mutant studies indicate that plus-charged residues and the scaffold-like structure of MGS are crucial for the vesiculation process. Hence, a number of features are involved governing the behaviour of monotopic membrane proteins at the lipid bilayer interface.
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| 20. |
- Ge, Changrong, 1980-, et al.
(författare)
-
Tryptophan residues promote membrane association for a plant lipid glycosyltransferase involved in phosphate stress
- 2011
-
Ingår i: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 286:8, s. 6669-6684
-
Tidskriftsartikel (refereegranskat)abstract
- Chloroplast membranes contain a substantial excess of the nonbilayer-prone monogalactosyldiacylglycerol (GalDAG) over the biosynthetically consecutive, bilayer-forming digalactosyldiacylglycerol (GalGalDAG), yielding a high membrane curvature stress. During phosphate shortage, plants replace phospholipids with GalGalDAG to rescue phosphate while maintaining membrane homeostasis. Here we investigate how the activity of the corresponding glycosyltransferase (GT) in Arabidopsis thaliana (atDGD2) depends on local bilayer properties by analyzing structural and activity features of recombinant protein. Fold recognition and sequence analyses revealed a two-domain GT-B monotopic structure, present in other plant and bacterial glycolipid GTs, such as the major chloroplast GalGalDAG GT atDGD1. Modeling led to the identification of catalytically important residues in the active site of atDGD2 by site-directed mutagenesis. The DGD synthases share unique bilayer interface segments containing conserved tryptophan residues that are crucial for activity and for membrane association. More detailed localization studies and liposome binding analyses indicate differentiated anchor and substrate-binding functions for these separated enzyme interface regions. Anionic phospholipids, but not curvature-increasing nonbilayer lipids, strongly stimulate enzyme activity. From our studies, we propose a model for bilayer "control" of enzyme activity, where two tryptophan segments act as interface anchor points to keep the substrate region close to the membrane surface. Binding of the acceptor substrate is achieved by interaction of positive charges in a surface cluster of lysines, arginines, and histidines with the surrounding anionic phospholipids. The diminishing phospholipid fraction during phosphate shortage stress will then set the new GalGalDAG/phospholipid balance by decreasing stimulation of atDGD2.
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| 21. |
- Georgiev, Alexander, et al.
(författare)
-
Basic clusters and amphipathic helices contribute to interactions of Myr1/Syh1 with membrane phospholipids
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The ability to associate transiently with membrane bilayers is an important property of many protein regulators of membrane trafficking, lipid transfer proteins, or signaling modules. Membrane association is also a property of Myr1/Syh1, a soluble GYF domain protein from Saccharomyces cerevisiae, previously reported to rescue the temperature sensitive growth of ypt6 and ric1 null strains. Here, we further demonstrate that MYR1 also rescued the vacuole fragmentation phenotype of the ypt6 and ric1 mutants. The mechanism behind these genetic interactions is likely linked to the capacity of the Myr1/Syh1 protein to associate with phospholipid membranes. In order to elucidate further the nature of the interactions with vesicular traffic, we studied protein-protein and protein-phospholipid association of isolated domains from Myr1/Syh1. Using a two-hybrid assay, we confirmed the capacity of Myr1/Syh1 to self-associate in vivo. We measured in vitro the affinity of recombinant Myr1/Syh1 domains fused to GFP for liposomes reconstituted from synthetic and natural yeast lipids by sedimentation techniques. The herewith established affinities of Myr1/Syh1 to specific lipids, combined with evidence for its interactions with membrane traffic and protein synthesis, provide support for a possible function of Myr1/Syh1 as a regulator sensing membrane composition along the vesicular pathways.
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| 22. |
- Georgiev, Alexander, et al.
(författare)
-
Binding specificities of the GYF domains from two Saccharomyces cerevisiae paralogs.
- 2007
-
Ingår i: Protein Eng Des Sel. - : Oxford University Press (OUP). - 1741-0126 .- 1741-0134. ; 20:9, s. 443-52
-
Tidskriftsartikel (refereegranskat)abstract
- We have used multivariate statistics and z-scales to represent peptide sequencesin a PLS-QSAR model of previously studied binding affinities [Kofler,M.,Motzny,K. and Freund,C. (2005b) Mol. Cell. Proteomics, 4, 1797-1811.] of two GYFdomains to an array of immobilized synthetic peptides. As a result, weestablished structural determinants of the binding specificities of the twoproteins. Our model was used to define new sets of yeast proteins potentiallyinteracting with Syh1 (YPL105C) and Smy2 (YBR172C). These sets were subsequentlyexamined for co-occurrence of Gene Ontology terms, leading to suggest a group oflikely interacting proteins with a common function in mRNA catabolism. Finally,subcellular localization of a GFP-fused Syh1 and Smy2 reinforced the possibilitythat these proteins reside in cytoplasmic sites of mRNA degradation, therebyproviding experimental confirmation to the predictions from the model.
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| 23. |
- Georgiev, Alexander, 1973-
(författare)
-
Membrane Stress and the Role of GYF Domain Proteins
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intracellular membrane trafficking is regulated by a large number of protein complexes and lipids. Blocking of trafficking disrupts normal membrane dynamics and causes membrane stress. Two similar proteins from Saccharomyces cerevisiae, Myr1 and Smy2, each containing a polyproline-binding GYF domain, were discovered in separate screens for dosage suppressors of trafficking mutations. The functions of GYF domain proteins are poorly described despite its determined structure and a number of known polyproline peptide ligands. We predicted, using computational analysis, associations between mRNA decay factors and both Myr1 and Smy2, and further demonstrated that they localize to sites of mRNA degradation upon stress, in a GYF domain dependent manner.Ypt6 is a small GTPase that regulates vesicle docking at the late Golgi in budding yeast. Myr1 was found as a novel suppressor during the screening of a genomic library in a null ypt6 mutant. Myr1 additionally was capable of rescuing the temperature sensitive growth of a Ric1 deficient strain. Importantly, Ric1 is an activator of Ypt6 and is synthetic lethal with Myr1. Biochemical characterization of the Myr1 protein revealed a limited solubility and an ability to bind cellular membranes, likely relevant to the rescue of trafficking mutants.We further assayed the affinity of Myr1 domains to liposomes of distinct composition. Preference for negatively charged lipids suggested possible electrostatic interactions with polybasic clusters within C-terminal regions of Myr1. In contrast, the N-terminus with the GYF domain was found to be capable of self-association. Membrane stress caused by a lipid-bilayer perturbing drug resulted in induced formation of mRNA processing bodies. Cumulatively, these studies suggest that Myr1 functions in the regulation of mRNA stability via its GYF domain, and can sense membrane stress by binding to the lipid bilayer.
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| 24. |
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| 25. |
- Keller, Rebecca, et al.
(författare)
-
The Escherichia coli envelope stress sensor CpxA can sense changes in lipid bilayer properties
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Membrane proteins are evolutionarily integrated with their lipid bilayer environment, but it is only marginally understood how they sense and adapt to changes in lipid composition. Here we use an in vitro reconstitution system to demonstrate that the activity of envelope stress sensor CpxA of Escherichia coli is modulated by lipid bilayer properties. By changing the lipid composition of the vesicles, and using lipid-engineered E. coli strains we show that CpxA activity is regulated by means of different properties of the bilayer: (i) anionic surface charge (ii) membrane curvature (iii) thus lateral bilayer stress but also (iv) membrane bilayer thickness. We conclude that the CpxA could sense changes in the lipid bilayer properties.
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| 26. |
- Keller, Rebecca, et al.
(författare)
-
The Escherichia coli envelope stress sensor CpxA can sense changes in lipid bilayer properties
- 2015
-
Ingår i: ACS Biochemistry. ; 54:23, s. 3670-3676
-
Tidskriftsartikel (refereegranskat)abstract
- The Cpx stress response system is induced by various environmental and cellular stimuli. It is also activated in Escherichia coli strains lacking the major phospholipid, phosphatidylethanolamine (PE). However, it is not known whether CpxA directly senses changes in the lipid bilayer or the presence of misfolded proteins due to the lack of PE in their membranes. To address this question, we used an in vitro reconstitution system and vesicles with different lipid compositions to track modulations in the activity of CpxA in different lipid bilayers. Moreover, the Cpx response was validated in vivo by monitoring expression of a PcpxP-gfp reporter in lipid-engineered strains of E. coli. Our combined data indicate that CpxA responds specifically to different lipid compositions.
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| 27. |
- Keller, Rebecca, et al.
(författare)
-
The Escherichia coli Envelope Stress Sensor CpxA Responds to Changes in Lipid Bilayer Properties
- 2015
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 54:23, s. 3670-3676
-
Tidskriftsartikel (refereegranskat)abstract
- The Cpx stress response system is induced by various environmental and cellular stimuli. It is also activated in Escherichia coli strains lacking the major phospholipid, phosphatidylethanolamine (PE). However, it is not known whether CpxA directly senses changes in the lipid bilayer or the presence of misfolded proteins due to the lack of PE in their membranes. To address this question, we used an in vitro reconstitution system and vesicles with different lipid compositions to track modulations in the activity of CpxA in different lipid bilayers. Moreover, the Cpx response was validated in vivo by monitoring expression of a PcpxP-gfp reporter in lipid-engineered strains of E. coli. Our combined data indicate that CpxA responds specifically to different lipid compositions.
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| 28. |
- Lagerstedt, Jens O., 1975, et al.
(författare)
-
Structural modeling of dual-affinity purified Pho84 phosphate transporter
- 2004
-
Ingår i: FEBS Lett. - : Wiley. - 0014-5793 .- 1873-3468. ; 578:3, s. 262-8
-
Tidskriftsartikel (refereegranskat)abstract
- The phosphate transporter Pho84 of Saccharomyces cerevisiae is predicted to contain 12 transmembrane (TM) regions, divided into two partially duplicated parts of 6 TM segments. The three-dimensional (3D) organization of the Pho84 protein has not yet been determined. However, the 3D crystal structure of the Escherichia coli MFS glycerol-3-phosphate/phosphate antiporter, GlpT, and lactose transporter, LacY, has recently been determined. On the basis of extensive prediction and fold recognition analyses (at the MetaServer), GlpT was proposed as the best structural template on which the arrangement of TM segments of the Pho84 transporter was fit, using the comparative structural modeling program MODELLER. To initiate an evaluation of the appropriateness of the Pho84 model, we have performed two direct tests by targeting spin labels to putative TM segments 8 and 12. Electron paramagnetic resonance spectroscopy was then applied on purified and spin labeled Pho84. The line shape from labels located at both positions is consistent with the structural environment predicted by the template-generated model, thus supporting the model.
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| 29. |
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| 30. |
- Lind, Jesper, et al.
(författare)
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High cationic charge and bilayer interface-binding helices in a regulatory lipid glycosyltransferase
- 2007
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 46:19, s. 5664-5677
-
Tidskriftsartikel (refereegranskat)abstract
- In the prokaryote Acholeplasma laidlawii, membrane bilayer properties are sensed and regulated by two interface glycosyltransferases (GTs), synthesizing major nonbilayer- (alMGS GT) and bilayer-prone glucolipids. These enzymes are of similar structure, as many soluble GTs, but are sensitive to lipid charge and curvature stress properties. Multivariate and bioinformatic sequence analyses show that such interface enzymes, in relation to soluble ones of similar fold, are characterized by high cationic charge, certain distances between small and cationic amino acids, and by amphipathic helices. Varying surface contents of Lys/Arg pairs and Trp indicate different membrane-binding subclasses. A predicted potential (cationic) binding helix from alMGS was structurally verified by solution NMR and CD. The helix conformation was induced by a zwitterionic as well as anionic lipid environment, and the peptide was confined to the bilayer interface. Bilayer affinity of the peptide, analyzed by surface plasmon resonance, was higher than that for soluble membrane-seeking proteins/peptides and rose with anionic lipid content. Interface intercalation was supported by phase equilibria in membrane lipid mixtures, analyzed by 31P NMR and DSC. An analogous, potentially binding helix has a similar location in the structurally determined Escherichia coli cell wall precursor GT MurG. These two helices have little sequence conservation in alMGS and MurG homologues but maintain their amphipathic character. The evolutionary modification of the alMGS binding helix and its location close to the acceptor substrate site imply a functional importance in enzyme catalysis, potentially providing a mechanism by which glycolipid synthesis will be sensitive to membrane surface charge and intrinsic curvature strain.
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| 31. |
- Lindholm, Ljubica, et al.
(författare)
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Effect of lipid bilayer properties on the photocycle of green proteorhodopsin
- 2015
-
Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1847:8, s. 698-708
-
Tidskriftsartikel (refereegranskat)abstract
- The significance of specific lipids for proton pumping by the bacterial rhodopsin proteorhodopsin (pR) was studied. To this end, it was examined whether pR preferentially binds certain lipids and whether molecular properties of the lipid environment affect the photocycle. pR's photocyde was followed by microsecond flash-photolysis in the visible spectral range. It was fastest in phosphatidylcholine liposomes (soy bean lipid), intermediate in 3-[(3-cholamidopropyl) dimethylammonio] propanesulfonate (CHAPS): 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bicelles and in Triton X-100, and slowest when pR was solubilized in CHAPS. In bicelles with different lipid compositions, the nature of the head groups, the unsaturation level and the fatty acid chain length had small effects on the photocycle. The specific affinity of pR for lipids of the expression host Eschetichia coil was investigated by an optimized method of lipid isolation from purified membrane protein using two different concentrations of the detergent N-dodecyl-beta-D-maltoside (DDM). We found that 11 lipids were copurified per pR molecule at 0.1% DDM, whereas essentially all lipids were stripped off from pR by 1% DDM. The relative amounts of copurifled phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin did not correlate with the molar percentages normally present in E. coil cells. The results indicate a predominance of phosphatidylethanolamine species in the lipid annulus around recombinant pR that are less polar than the dominant species in the cell membrane of the expression host E. coli.
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| 32. |
- Muheim, Claudio, et al.
(författare)
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Identification of a Fragment-Based Scaffold that Inhibits the Glycosyltransferase WaaG from Escherichia coli
- 2016
-
Ingår i: Antibiotics. - : MDPI AG. - 2079-6382. ; 5:1
-
Tidskriftsartikel (refereegranskat)abstract
- WaaG is a glycosyltransferase that is involved in the biosynthesis of lipopolysaccharide in Gram-negative bacteria. Inhibitors of WaaG are highly sought after as they could be used to inhibit the biosynthesis of the core region of lipopolysaccharide, which would improve the uptake of antibiotics. Herein, we establish an activity assay for WaaG using C-14-labeled UDP-glucose and LPS purified from a increment waaG strain of Escherichia coli. We noted that addition of the lipids phosphatidylglycerol (PG) and cardiolipin (CL), as well as the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) increased activity. We then use the assay to determine if three molecular scaffolds, which bind to WaaG, could inhibit its activity in vitro. We show that 4-(2-amino-1,3-thiazol-4-yl)phenol inhibits WaaG (IC50 1.0 mM), but that the other scaffolds do not. This study represents an important step towards an inhibitor of WaaG by fragment-based lead discovery.
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| 33. |
- Pisareva, Tatiana, et al.
(författare)
-
Model for Membrane Organization and Protein Sorting in the Cyanobacterium Synechocystis sp. PCC 6803 Inferred from Proteomics and Multivariate Sequence Analyses
- 2011
-
Ingår i: Journal of Proteome Research. - : American Chemical Society (ACS). - 1535-3893 .- 1535-3907. ; 10:8, s. 3617-3631
-
Tidskriftsartikel (refereegranskat)abstract
- Cyanobacteria are unique eubacteria with an organized subcellular compartmentalization of highly differentiated internal thylakoid membranes (TM), in addition to the outer and plasma membranes (PM). This leads to a complicated system for transport and sorting of proteins into the different membranes and compartments. By shotgun and gel-based proteomics of plasma and thylakoid membranes from the cyanobacterium Synechocystis sp. PCC 6803, a large number of membrane proteins were identified. Proteins localized uniquely in each membrane were used as a platform describing a model for cellular membrane organization and protein intermembrane sorting and were analyzed by multivariate sequence analyses to trace potential differences in sequence properties important for insertion and sorting to the correct membrane. Sequence traits in the C-terminal region, but not in the N-terminal nor in any individual transmembrane segments, were discriminatory between the TM and PM classes. The results are consistent with a contact zone between plasma and thylakoid membranes, which may contain short-lived "hemifusion" protein traffic connection assemblies. Insertion of both integral and peripheral membrane proteins is suggested to occur through common translocons in these subdomains, followed by a potential translation arrest and structure-based sorting into the correct membrane compartment.
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| 34. |
- Rajalahti, Tarja, et al.
(författare)
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Proteins in different Synechocystis compartments have distinguishing N-terminal features : a combined proteomics and multivariate sequence analysis
- 2007
-
Ingår i: Journal of Proteome Research. - : American Chemical Society (ACS). - 1535-3893 .- 1535-3907. ; 6:7, s. 2420-2434
-
Tidskriftsartikel (refereegranskat)abstract
- Cyanobacteria have a cell envelope consisting of a plasma membrane, a periplasmic space with a peptidoglycan layer, and an outer membrane. A third, separate membrane system, the intracellular thylakoid membranes, is the site for both photosynthesis and respiration. All membranes and luminal spaces have unique protein compositions, which impose an intriguing mechanism for protein sorting of extracytoplasmic proteins due to single sets of translocation protein genes. It is shown here by multivariate sequence analyses of many experimentally identified proteins in Synechocystis, that proteins routed for the different extracytosolic compartments have correspondingly different physicochemical properties in their signal peptide and mature N-terminal segments. The full-length mature sequences contain less significant information. From these multivariate, N-terminal property-profile models for proteins with single experimental localization, proteins with ambiguous localization could, to a large extent, be predicted to a defined compartment. The sequence properties involve amino acids varying especially in volume and polarizability and at certain positions in the sequence segments, in a manner typical for the various compartment classes. Potential means of the cell to recognize the property features are discussed, involving the translocation channels and two Type I signal peptidases with different cellular localization, and charge features at their membrane interfaces.
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| 35. |
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| 36. |
- Rosén Klement, Maria L., et al.
(författare)
-
A processive lipid glycosyltransferase in the small human pathogen Mycoplasma pneumoniae: involvement in host immune response
- 2007
-
Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 65:6, s. 1444-1457
-
Tidskriftsartikel (refereegranskat)abstract
- The human pathogen Mycoplasma pneumoniae has a very small genome but with many yet not identified gene functions, e.g. for membrane lipid biosynthesis. Extensive radioactive labelling in vivo and enzyme assays in vitro revealed a substantial capacity for membrane glycolipid biosynthesis, yielding three glycolipids, five phosphoglycolipids, in addition to six phospholipids. Most glycolipids were synthesized in a cell protein/lipid-detergent extract in vitro; galactose was incorporated into all species, whereas glucose only into a few. One (MPN483) of the three predicted glycosyltransferases (GTs; all essential) was both processive and promiscuous, synthesizing most of the identified glycolipids. These enzymes are of a GT-A fold, similar to an established structure, and belong to CAZy GT-family 2. The cloned MPN483 could use both diacylglycerol (DAG) and human ceramide acceptor substrates, and in particular UDP-galactose but also UDP-glucose as donors, making mono-, di- and trihexose variants. MPN483 output and processitivity was strongly influenced by the local lipid environment of anionic lipids. The structure of a major β1,6GlcβGalDAG species was determined by NMR spectroscopy. This, as well as other purified M. pneumoniae glycolipid species, is important antigens in early infections, as revealed from ELISA screens with patient IgM sera, highlighting new aspects of glycolipid function.
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| 37. |
- Rosén Klement, Maria, 1975-
(författare)
-
The advantages of being small : Glycosyltransferases in many dimensions and glycolipid synthesis in Mycoplasma Pneumoniae
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The synthesis and breakdown of sugars is one of the most important functions in Nature. Consequently, sugar structures are used both as energy storage and as building blocks to stabilise and protect the cell. The formation of these structures is performed by glycosyltransferases (GT), an enzyme group structurally conserved within all kingdoms. Until now, only two different folds have been discovered by crystallisation of GTs, i.e. GT-A and GT-B. A third fold family has however been proposed by fold predictions. In this thesis, a multivariate data analysis was successfully used in classifying and predicting both fold and reaction mechanism (inverting or retaining) of GTs. This method was also used to obtain information about the separating parameters for the reaction mechanism classification. This information could be traced back to the amino acid sequence. The method could as well be used to analyse and identify the properties of membrane binding regions of GTs, and subsequently distinguish soluble from membrane-associated enzymes. Most functionally characterised enzymes only use one substrate, synthesising one product. Mycoplasma pneumoniae, a common human pathogen with a small genome has only three proposed GTs. The bacterium was, however expected to have a greater number of GTs, due to its ability to make both glycolipids and capsule. Here we have determined the function of one of these enzymes, MPN483 and discovered its ability to both use different acceptors, and make elongated glycolipids with up to three galactose residues, with both DAG and ceramide as the base. Many of the synthesised glycolipids were also found to be immunogenic, hence showing their biological importance. The properties of lipids are known to be important for the function of a biological membrane. We have here shown that not only the charge but also the shape of the lipids are important for several protein mediated membrane processes in Echerichia coli, such as the function of the LacY.
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| 38. |
- Rosén, Maria L, et al.
(författare)
-
Recognition of Fold and Sugar Linkage for Glycosyltransferases by Multivariate Sequence Analysis
- 2004
-
Ingår i: Journal of Biological Chemistry. ; 279, s. 38683-92
-
Tidskriftsartikel (refereegranskat)abstract
- Glycosyltransferases (GTs) are among the largest groups of enzymes found and are usually classified on the basis of sequence comparisons into many families of varying similarity (CAZy systematics). Only two different Rossman-like folds have been detected (GT-A and GT-B) within the small number of established crystal structures. A third uncharacterized fold has been indicated with transmembrane organization (GT-C). We here use a method based on multivariate data analyses (MVDAs) of property patterns in amino acid sequences and can with high accuracy recognize the correct fold in a large data set of GTs. Likewise, a retaining or inverting enzymatic mechanism for attachment of the donor sugar could be properly revealed in the GT-A and GT-B fold group sequences by such analyses. Sequence alignments could be correlated to important variables in MVDA, and the separating amino acid positions could be mapped over the active sites. These seem to be localized to similar positions in space for the // binding motifs in the GT-B fold group structures. Analogous, active-site sequence positions were found for the GT-A fold group. Multivariate property patterns could also easily group most GTs annotated in the genomes of Escherichia coli and Synechocystis to proper fold or organization group, according to benchmarking comparisons at the MetaServer. We conclude that the sequence property patterns revealed by the multivariate analyses seem more conserved than amino acid types for these GT groups, and these patterns are also conserved in the structures. Such patterns may also potentially define substrate preferences.
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| 39. |
- Selao, Tiago Toscano, et al.
(författare)
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Subcellular Localization of Monoglucosyldiacylglycerol Synthase in Synechocystis sp PCC6803 and Its Unique Regulation by Lipid Environment
- 2014
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:2, s. e88153-
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis of monogalactosyldiacylglycerol (GalDAG) and digalactosyldiacylglycerol (GalGalDAG), the major membrane lipids in cyanobacteria, begins with production of the intermediate precursor monoglucosyldiacylglycerol (GlcDAG), by monoglucosyldiacylglycerol synthase (MGS). In Synechocystis sp. PCC6803 (Synechocystis) this activity is catalyzed by an integral membrane protein, Sll1377 or MgdA. In silico sequence analysis revealed that cyanobacterial homologues of MgdA are highly conserved and comprise a distinct group of lipid glycosyltransferases. Global regulation of lipid synthesis in Synechocystis and, more specifically, the influence of the lipid environment on MgdA activity have not yet been fully elucidated. Therefore, we purified membrane subfractions from this organism and assayed MGS activity in vitro, with and without different lipids and other potential effectors. Sulfoquinovosyldiacylglycerol (SQDAG) potently stimulates MgdA activity, in contrast to other enzymes of a similar nature, which are activated by phosphatidylglycerol instead. Moreover, the final products of galactolipid synthesis, GalDAG and GalGalDAG, inhibited this activity. Western blotting revealed the presence of MgdA both in plasma and thylakoid membranes, with a high specific level of the MgdA protein in the plasma membrane but highest MGS activity in the thylakoid membrane. This discrepancy in the subcellular localization of enzyme activity and protein may indicate the presence of either an unknown regulator and/or an as yet unidentified MGS-type enzyme. Furthermore, the stimulation of MgdA activity by SQDAG observed here provides a new insight into regulation of the biogenesis of both sulfolipids and galactolipids in cyanobacteria.
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| 40. |
- Szpryngiel, Scarlett, et al.
(författare)
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Lipid Interacting Regions in Phosphate Stress Glycosyltransferase atDGD2 from Arabidopsis thaliana
- 2011
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 50:21, s. 4451-4466
-
Tidskriftsartikel (refereegranskat)abstract
- Membrane lipid glycosyltransferases (GTs) in plants are enzymes that regulate the levels of the non-bilayer prone monogalactosyldiacylglycerol (GalDAG) and the bilayer-forming digalactosyldiacylglycerol (GalGalDAG). The relative amounts of these lipids affect membrane properties such as curvature and lateral stress. During phosphate shortage, phosphate is rescued by replacing phospholipids with GalGalDAG. The glycolsyltransferase enzyme in Arabidopsis thaliana responsible for this, atDGD2, senses the bilayer properties and interacts with the membrane in a monotopic manner. To understand the parameters that govern this interaction, we have identified several possible lipid-interacting sites in the protein and studied these by biophysical techniques. We have developed a multivariate discrimination algorithm that correctly predicts the regions in the protein that interact with lipids, and the interactions were confirmed by a variety of biophysical techniques. We show by bioinformatic methods and circular dichroism (CD), fluorescence, and NMR spectroscopic techniques that two regions are prone to interact with lipids in a surface-charge dependent way. Both of these regions contain Trp residues, but here charge appears to be the dominating feature governing the interaction. The sequence corresponding to residues 227–245 in the protein is seen to be able to adapt its structure according to the surface-charge density of a bilayer. All results indicate that this region interacts specifically with lipid molecules and that a second region in the protein, corresponding to residues 130–148, also interacts with the bilayer. On the basis of this, and sequence charge features in the immediate environment of S227–245, a response model for the interaction of atDGD2 with the membrane bilayer interface is proposed.
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| 41. |
- Tjellström, Henrik, 1974, et al.
(författare)
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Lipid asymmetry in plant plasma membranes : phosphate deficiency-induced phospholipid replacement is restricted to the cytosolic leaflet
- 2010
-
Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 24:4, s. 1128-1138
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Tidskriftsartikel (refereegranskat)abstract
- As in other eukaryotes, plant plasma membranes contain sphingolipids, phospholipids, and free sterols. In addition, plant plasma membranes also contain sterol derivatives and usually <5 mol% of a galactolipid, digalactosyldiacylglycerol (DGDG). We earlier reported that compared to fully fertilized oats (Avena sativa), oats cultivated without phosphate replaced up to 70 mol% of the root plasma membrane phospholipids with DGDG. Here, we investigated the implications of a high DGDG content on membrane properties. The phospholipid-to-DGDG replacement almost exclusively occurred in the cytosolic leaflet, where DGDG constituted up to one-third of the lipids. In the apoplastic (exoplasmic) leaflet, as well as in rafts, phospholipids were not replaced by DGDG, but by acylated sterol glycosides. Liposome studies revealed that the chain ordering in free sterol/phospholipid mixtures clearly decreased when > 5mol% DGDG was included. As both the apoplastic plasma membrane leaflet (probably the major water permeability barrier) and rafts both contain only trace amounts of DGDG, we conclude that this lipid class is not compatible with membrane functions requiring a high degree of lipid order. By not replacing phospholipids site specifically with DGDG, negative functional effects of this lipid in the plasma membrane are avoided.
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- Wikström, Malin, 1974-
(författare)
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Synthesis and protein curing abilities of membrane glycolipids
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There are many types of membrane lipids throughout Nature. Still little is known about synthesizing pathways and how different lipids affect the embedded membrane proteins. The most common lipids are glycolipids since they dominate plant green tissue. Glycolipids also exist in mammal cells as well as in most Gram-positive bacteria. Glycosyltransferases (GTs) catalyze the final enzymatic steps for these glycolipids. In the bacteria Acholeplasma laidlawii and Streptococcus pneumonie and in the plant Arabidopsis thaliana, GTs for mono-/di-glycosyl-diacylglycerol (-DAG) are suggested to be regulated to keep a certain membrane curvature close to a bilayer/nonbilayer phase transition. The monoglycosylDAGs are nonbilayer-prone with small headgroups, hence by themselves they will not form bilayer structures.Here we have determined the genes encoding the main glycolipids of A. laidlawii and S. pneumonie. We have also shown that these GTs belong to a large enzyme group widely spread in Nature, and that all four enzymes are differently regulated by membrane lipids. The importance of different lipid properties were traced in a lipid mutant of Escherichia coli lacking the major (75 %), nonbilayer-prone/zwitterionic, lipid phosphatidylethanolamine. Introducing the genes for the GTs of A. laidlawii and two analogous genes from A. thaliana yielded new strains containing 50 percent of glyco-DAG lipids. The monoglyco-DAG strains contain significant amounts of nonbilayer-prone lipids while the diglyco-DAG strains contain no such lipids. Comparing these new strains for viability and the state of membrane-associated functions made it possible to connect different functions to certain lipid properties. In summary, a low surface charge density of anionic lipids is important in E.coli membranes, but this fails to be supportive if the diluting species have a too large headgroup. This indicates that a certain magnitude of the curvature stress is crucial for the membrane bilayer in vivo.
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