| 231. |
|
|
| 232. |
- Stanne, Tara M, 1979, et al.
(författare)
-
Identification of new protein substrates for the chloroplast ATP-dependent Clp protease supports its constitutive role in Arabidopsis.
- 2009
-
Ingår i: The Biochemical journal. - 1470-8728. ; 417:1, s. 257-68
-
Tidskriftsartikel (refereegranskat)abstract
- The ATP-dependent Clp protease in plant chloroplasts consists of a heterogeneous proteolytic core containing multiple ClpP and ClpR paralogues. In this study, we have examined in detail the only viable knockout mutant to date of one of these subunits in Arabidopsis thaliana, ClpR1. Loss of ClpR1 caused a slow-growth phenotype, with chlorotic leaves during early development that later partially recovered upon maturity. Analysis of the Clp proteolytic core in the clpR1 mutant (clpR1-1) revealed approx. 10% of the wild-type levels remaining, probably due to a relative increase in the closely related ClpR3 protein and its partial substitution of ClpR1 in the core complex. A proteomic approach using an in organello proteolytic assay revealed 19 new potential substrates for the chloroplast Clp protease. Many of these substrates were constitutive enzymes involved in different metabolic pathways, including photosynthetic carbon fixation, nitrogen metabolism and chlorophyll/haem biosynthesis, whereas others function in housekeeping roles such as RNA maturation, protein synthesis and maturation, and recycling processes. In contrast, degradation of the stress-related chloroplast proteins Hsp21 (heat-shock protein 21) and lipoxygenase 2 was unaffected in the clpR1-1 line and thus not facilitated by the Clp protease. Overall, we show that the chloroplast Clp protease is principally a constitutive enzyme that degrades numerous stromal proteins, a feature that almost certainly underlies its vital importance for chloroplast function and plant viability.
|
|
| 233. |
- StrzeleckaGolaszewska, H, et al.
(författare)
-
Effects of the type of divalent cation, Ca2+ or Mg2+, bound at the high-affinity site and of the ionic composition of the solution on the structure of F-actin
- 1996
-
Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 316316 ( Pt 3), s. 713-721
-
Tidskriftsartikel (refereegranskat)abstract
- F-actins containing either Ca2+ or Mg2+ at the single high-affinity site for a divalent cation differ in their dynamic properties [Carlier (1991) J. Biol. Chem. 266, 1–4]. In an attempt to obtain information on the structural basis of this difference, we probed the conformation of specific sites in the subunits of Mg- and Ca-F-actin with limited proteolysis by subtilisin and trypsin. The influence of the kind of polymerizing salt was also investigated. At high proteinase concentrations required for digestion of actin in the polymer form, subtilisin gives a complex fragmentation pattern. In addition to the earlier known cleavage between Met47 and Gly48 in the DNAse-I-binding loop, cleavage of F-actin between Ser234 and Ser235 in subdomain 4 has recently been reported [Vahdat, Miller, Phillips, Muhlrad and Reisler (1995) FEBS Lett. 365, 149–151]. Here we show that actually a larger segment, comprising residues 227–235, is removed and the bond between Leu67 and Lys68 in subdomain 2 is split in both G- and F-actin, and that the differences in the fragmentation patterns of the G- and F-forms are accounted for by the protection of the bond 47–48 in F-actin. The subtilisin and trypsin cleavage sites in segment 61–69, subtilisin sites in segment 227–235 and trypsin sites between Lys373 and Cys374 were less accessible in Mg-F-actin than in Ca-F-actin. These are intramolecular effects, as similar changes were observed on Ca2+/Mg2+ replacement in G-actin. The cation-dependent effects, in particular those on segment 61–69, were however less pronounced in F-actin than in G-actin. The results suggest that substitution of Mg2+ for Ca2+, and KCl-induced polymerization of CaATP-G-actin, bring about a similar change in the conformation of subdomain 2 of the monomer. The presence of Mg2+ at the high-affinity site also resulted in an increased protection of the bond 47–48. This latter appears to be an intermolecular effect because it is specific for F-actin. The susceptibility to subtilisin and trypsin was also strongly influenced by the kind and concentration of polymerizing salt. The digestion patterns suggest that the exposure and/or flexibility of the regions containing the cleavage sites diminish with enhancement of the ionic strength of the solution. The results are discussed in terms of the current models of F-actin.
|
|
| 234. |
- Sui, GC, et al.
(författare)
-
Functional effects of single amino acid substitutions in the region of Phe113 to Asp138 in the plasminogen activator inhibitor 1 molecule
- 1998
-
Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 331331 ( Pt 2), s. 409-415
-
Tidskriftsartikel (refereegranskat)abstract
- Thirteen amino acid substitutions have been introduced within the stretch Phe113 to Asp138 in the plasminogen activator inhibitor 1 (PAI-1) molecule by site-directed mutagenesis. The different proteins and wild-type (wt) PAI-1 have been overexpressed in Escherichia coliand purified by chromatography on heparin–Sepharose and on anhydrotrypsin–agarose. The PAI-1 variants have been characterized by their reactivity with tissue plasminogen activator (tPA), interactions with vitronectin or heparin, and stability. Most PAI-1 variants, except for Asp125 → Lys, Phe126 → Ser and Arg133 → Asp, displayed a high spontaneous inhibitory activity towards tPA, which did not change greatly on reactivation with 4 M guanidinium chloride, followed by dialysis at pH 5.5. The variants Asp125 → Lys and Arg133 → Asp became much more active after reactivation and they were also more rapidly transformed to inactive forms (t½ 22–31 min) at physiological pH and temperature than the other variants. However, in the presence of vitronectin they were both almost equally stable (t½ 2.3 h) as wtPAI-1 (t½ 3.0 h). The mutant Glu130 → Lys showed an increased stability, both in the absence and in the presence of vitronectin compared with wtPAI-1. Nevertheless a similar affinity between all the active PAI-1 variants and vitronectin was observed. Further, all mutants, including the three mutants with low activity, were to a large extent adsorbed on anhydrotrypsin–agarose and were eluted in a similar fashion. In accordance with these data, the three variants with a low activity were all to a large extent cleaved as a result of their reaction with tPA, suggesting that they occurred predominantly in the substrate conformation. Our results do not support the presence of a binding site for vitronectin in this part of the molecule, but rather that it might be involved in controlling the active PAI-1 to substrate transition. Partly, this region of the PAI-1 molecule (Arg115 to Arg118) seems also to be involved in the binding of heparin to PAI-1.
|
|
| 235. |
- Sun, TH, et al.
(författare)
-
Binding of glutathione and an inhibitor to microsomal glutathione transferase
- 1997
-
Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 326326 ( Pt 1), s. 193-196
-
Tidskriftsartikel (refereegranskat)abstract
- Microsomal glutathione transferase is an abundant liver protein that can be activated by thiol reagents. It is not known whether the activation is associated with changed binding properties of the enzyme. Therefore the binding of GSH and an inhibitor to rat liver microsomal glutathione transferase was studied by use of equilibrium dialysis and equilibrium partition in a two-phase system. The radioactive substrate glutathione and an inhibitor (glutathione sulphonate) give hyperbolic binding isotherms with a stoichiometry of 1 mol per mol of enzyme (i.e. 1 molecule per homotrimer). Glutathione had an equilibrium binding constant of 18 μM. Competition experiments involving glutathione sulphonate showed that it could effectively displace GSH. These and kinetic studies showed that the Kd and Ki for glutathione sulphonic acid are close to 10 μM. No change in these parameters was obtained after N-ethylmaleimide activation of the enzyme. Thus activation does not result from changes in binding affinity to GSH.
|
|
| 236. |
|
|
| 237. |
- Sundberg, K, et al.
(författare)
-
Studies on the differential inhibition of glutathione conjugate formation of (+)-anti-benzo[a]pyrene 7,8-dihydrodiol 9,10-epoxide and 1-chloro-2,4-dinitrobenzene in V79 Chinese hamster cells
- 2000
-
Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 349349 Pt 3, s. 693-696
-
Tidskriftsartikel (refereegranskat)abstract
- V79 Chinese hamster cells have previously been shown to lack the capacity to detoxify the mutagenic and carcinogenic compound (+)-anti-benzo[a]pyrene 7,8-dihydrodiol 9,10-epoxide [(+)-anti-BPDE] by Pi class glutathione transferase (GSTPi)-catalysed conjugation with GSH, although these cells contain such an enzyme [Romert, Dock, Jenssen and Jernström (1989) Carcinogenesis 10, 1701–1707; Swedmark, Romert, Morgenstern and Jenssen (1992) Carcinogenesis 13, 1719–1723; Swedmark and Jenssen (1994) Gene 139, 251–256]. Previous findings also indicate that these results do not depend on an inactive GSTPi enzyme, since V79 cells conjugate 1-chloro-2,4-dinitrobenzene (CDNB) with GSH, but more likely on (a) factor(s) that inhibit(s) V79 GSTPi selectively [Swedmark, Jernström and Jenssen (1996) Biochem. J. 318, 533–538]. The present study demonstrates that both human and V79 recombinant GSTPi enzymes are inhibited with respect to conjugating (+)-anti-BPDE, but not CDNB, after pre-incubation with V79-cell extract, but not with MCF-7-cell extract. In addition, it was found that the inhibition is dependent on the amount of cell extract present and that the factor(s) is heat-resistant and has a molecular mass of less than 10 kDa, suggesting that the factor(s) is (are) non-proteinaceous in nature.
|
|
| 238. |
- Svensson, Daniel, et al.
(författare)
-
LL-37-induced host cell cytotoxicity depends on cellular expression of the globular C1q receptor (p33).
- 2016
-
Ingår i: The Biochemical journal. - 1470-8728. ; 473, s. 87-98
-
Tidskriftsartikel (refereegranskat)abstract
- The human host-defense peptide LL-37 not only displays antimicrobial activity but also immune modulating properties that trigger intracellular signaling events in host cells. Since the cytolytic activity of high LL-37 concentrations affects cell viability, the function of LL-37 requires tight regulation. Eukaryotic cells therefore benefit from protective measures to prevent harmful effects of LL-37. p33, also known as globular C1q receptor, is reported to act as an LL-37 antagonist by binding the peptide thereby reducing its cytotoxic activity. In this report, we show that high levels of endogenous p33 correlate with an increased viability in human cells treated with LL-37. Sub-cellular localization analysis showed p33 distribution at the mitochondria, the plasma membrane and in the cytosol. Strikingly, cytosolic over-expression of p33 significantly antagonized detrimental effects of LL-37 on cell fitness, while the reverse effect was observed by siRNA-induced down-regulation of p33. However, modulation of p33 expression had no effect on LL-37-induced plasma membrane pore forming capacity pointing to an intracellular mechanism. A scavenging function of intracellular p33 is further supported by co-immunoprecipitation experiments, showing a direct interaction between intracellular p33 and LL-37. Thus, our findings support an important role of intracellular p33 in maintaining cell viability by counteracting LL-37-induced cytotoxicity.
|
|
| 239. |
- Svensson, LT, et al.
(författare)
-
Molecular cloning and characterization of a mitochondrial peroxisome proliferator-induced acyl-CoA thioesterase from rat liver
- 1998
-
Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 329329 ( Pt 3), s. 601-608
-
Tidskriftsartikel (refereegranskat)abstract
- We have previously reported the purification and characterization of the peroxisome proliferator-induced very-long-chain acyl-CoA thioesterase (MTE-I) from rat liver mitochondria [L. T. Svensson, S. E. H. Alexson and J. K. Hiltunen (1995) J. Biol. Chem. 270, 12177-12183]. Here we describe the cloning of the corresponding cDNA. One full-length clone was isolated that contained an open reading frame of 1359 bp encoding a polypeptide with a calculated molecular mass of 49707 Da. The deduced amino acid sequence contains a putative mitochondrial leader peptide of 42 residues. Expression of the cDNA in Chinese hamster ovary cells, followed by immunofluorescence, immunoelectron microscopy and Western blot analyses, showed that the product was targeted to mitochondria and processed to a mature protein of 45 kDa, which is similar to the molecular mass of the protein isolated from rat liver mitochondria. The recombinant enzyme showed the same acyl-CoA chain-length specificity as the isolated rat liver enzyme. Sequence analysis showed no similarity to known esterases, but a high degree (approx. 40%) of identity with bile acid-CoA:amino acid N-acyltransferase cloned from human and rat liver. A putative active-site serine motif (Gly-Xaa-Ser-Xaa-Gly) of several carboxylesterases and lipases was identified. Western and Northern blot analyses showed that MTE-I is constitutively expressed in heart and is strongly induced in liver by feeding rats with di(2-ethylhexyl)phthalate, a peroxisome proliferator, suggesting a role for the enzyme in lipid metabolism.
|
|
| 240. |
- Svitacheva, Naila, et al.
(författare)
-
Biosynthesis of mucins in bovine trachea : identification of the major radiolabelled species
- 1998
-
Ingår i: Biochemical Journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 333:2, s. 449-456
-
Tidskriftsartikel (refereegranskat)abstract
- Bovine trachea in organ culture secretes mucus containing a 'high-density' (1.46 g/ml) and a 'low-density' (1.37 g/ml) mucin similar to those identified previously in bovine respiratory secretions [Hovenberg, Carlstedt and Davies (1997) Biochem. J. 321, 117-123]. After pulse-labelling, autoradiography showed uptake of [35S]sulphate by both epithelial goblet cells and submucosal glands, while [3H]proline was mainly incorporated into the ciliated surface epithelial cells. After 24 h of radiolabelling, neither the high- nor the low-density mucin in the secreted mucus gel was heavily radiolabelled with the precursors. In contrast, a population of molecules banding at 1.50 g/ml was heavily radiolabelled with [35S]sulphate. This component was smaller than the high-density mucin from the mucus gel and was insensitive to reduction or digestion with chondroitin ABC lyase or heparan sulphate lyase. The molecules yielded two populations of high-Mr glycopeptides upon trypsin digestion, were sensitive to keratanase and endo-beta-galactosidase digestion and contained O-linked glycans. Extracts of the surface epithelium and submucosal tissue after radiolabelling showed that the high- and low-density mucins in the tissue were also poorly radiolabelled. Thus, under these conditions, the radiolabelled precursors were not effectively incorporated into the large oligomeric mucins but into a high-Mr monomeric species. This study suggests that data obtained in investigations where mucins are radiolabelled and studied without further separation into distinct components may rather reflect the turnover of this 'novel' monomeric species than the large oligomeric mucins.
|
|
