| 1. |
- Gordon, Euan, 1971, et al.
(författare)
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Effective high-throughput overproduction of membrane proteins in Escherichia coli
- 2008
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Ingår i: Protein Expression and Purification. - : Elsevier BV. - 1096-0279 .- 1046-5928. ; 62:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Structural biology is increasingly reliant on elevated throughput methods for protein production. In particular, development of efficient methods of heterologous production of membrane proteins is essential. Here, we describe the heterologous overproduction of 24 membrane proteins from the human pathogen Legionella pneumophila in Escherichia coli. Protein production was performed in 0.5 ml cultures in standard 24-well plates, allowing increased throughput with minimal effort. The effect of the location of a histidine purification tag was analyzed, and the effect of decreasing the length of the N- and C-terminal extensions introduced by the Gateway cloning strategy is presented. We observed that the location and length of the purification tag significantly affected protein production levels. In addition, an auto-induction protocol for membrane protein expression was designed to enhance the overproduction efficiency such that, regardless of the construct used, much higher expression was achieved when compared with standard induction approaches such as isopropyl-β-d-thiogalactopyranoside (IPTG). All 24 targets were produced at levels exceeding 2 mg/l, with 18 targets producing at levels of 5 mg/l or higher. In summary, we have designed a fast and efficient process for the production of medically relevant membrane proteins with a minimum number of screening parameters.
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| 2. |
- Gunnarsson, Anders, 1981, et al.
(författare)
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Affinity Capturing and Surface Enrichment of a Membrane Protein Embedded in a Continuous Supported Lipid Bilayer
- 2016
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Ingår i: ChemistryOpen. - : Wiley. - 2191-1363. ; 5:5, s. 445-449
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Tidskriftsartikel (refereegranskat)abstract
- Investigations of ligand-binding kinetics to membrane proteins are hampered by their poor stability and low expression levels, which often translates into sensitivity-related limitations impaired by low signal-to-noise ratios. Inspired by affinity capturing of water-soluble proteins, which utilizes water as the mobile phase, we demonstrate affinity capturing and local enrichment of membrane proteins by using a fluid lipid bilayer as the mobile phase. Specific membrane-protein capturing and enrichment in a microfluidic channel was accomplished by immobilizing a synthesized trivalent nitrilotriacetic acid (tris-NTA)-biotin conjugate. A polymer-supported lipid bilayer containing His(6)-tagged b-secretase (BACE) was subsequently laterally moved over the capture region by using a hydrodynamic flow. Specific enrichment of His(6)-BACE in the Ni2+-NTA-modified region of the substrate resulted in a stationary three-fold increase in surface coverage, and an accompanied increase in ligand-binding response.
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| 3. |
- Gunnarsson, Anders, 1981, et al.
(författare)
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Drug Discovery at the Single Molecule Level: Inhibition-in-Solution Assay of Membrane-Reconstituted beta-Secretase Using Single-Molecule Imaging
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:8, s. 4100-4103
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Tidskriftsartikel (refereegranskat)abstract
- Inhibition-in-solution assays (ISA) employing surface-based biosensors such as surface plasmon resonance (SPR) are an effective screening approach in drug discovery. However, analysis of potent binders remains a significant hurdle due to limited sensitivity and accompanied depletion of the inhibiting compounds due to high protein concentrations needed for detectable binding signals. To overcome this limitation, we explored a microscopy-based single-molecule ISA compatible with liposome-reconstituted membrane proteins. Using a set of validated small molecule inhibitors against beta-secretase 1 (BACE1), the assay was benchmarked with respect to sensitivity and dynamic range against SPR. We demonstrate that the dynamic range of measurable affinities is greatly extended by more than 2 orders of magnitude as compared to SPR, thus facilitating measurements of highly potent (K-d
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| 4. |
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| 5. |
- Pace, Hudson, 1982, et al.
(författare)
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Preserved Transmembrane Protein Mobility in Polymer-Supported Lipid Bilayers Derived from Cell Membranes
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:18, s. 9194-9203
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Tidskriftsartikel (refereegranskat)abstract
- Supported lipid bilayers (SLBs) have contributed invaluable information about the physiochemical properties of cell membranes, but their compositional simplicity often limits the level of knowledge that can be gained about the structure and function of transmembrane proteins in their native environment. Herein, we demonstrate a generic protocol for producing polymer-supported lipid bilayers on glass surfaces that contain essentially all naturally occurring cell-membrane components of a cell line while still retaining transmembrane protein mobility and activity. This was achieved by merging vesicles made from synthetic lipids (PEGylated lipids and POPC lipids) with native cell-membrane vesicles to generate hybrid vesicles which readily rupture into a continuous polymer-supported lipid bilayer. To investigate the properties of these complex hybrid SLBs and particularly the behavior of their integral membrane-proteins, we used total internal reflection fluorescence imaging to study a transmembrane protease, β-secretase 1 (BACE1), whose ectoplasmic and cytoplasmic domains could both be specifically targeted with fluorescent reporters. By selectively probing the two different orientations of BACE1 in the resulting hybrid SLBs, the role of the PEG-cushion on transmembrane protein lateral mobility was investigated. The results reveal the necessity of having the PEGylated lipids present during vesicle adsorption to prevent immobilization of transmembrane proteins with protruding domains. The proteolytic activity of BACE1 was unadulterated by the sonication process used to merge the synthetic and native membrane vesicles; importantly it was also conserved in the SLB. The presented strategy could thus serve both fundamental studies of membrane biophysics and the production of surface-based bioanalytical sensor platforms.
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| 6. |
- Saline, Maria, et al.
(författare)
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AMPK and AKT protein kinases hierarchically phosphorylate the N-terminus of the FOXO1 transcription factor, modulating interactions with 14-3-3 proteins
- 2019
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 294:35, s. 13106-13116
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Tidskriftsartikel (refereegranskat)abstract
- Forkhead box protein O1 (FOXO1) is a transcription factor involved in various cellular processes such as glucose metabolism, development, stress resistance, and tumor suppression. FOXO1's transcriptional activity is controlled by different environmental cues through a myriad of posttranslational modifications. In response to growth factors, the serine/threonine kinase AKT phosphorylates Thr24 and Ser256 in FOXO1 to stimulate binding of 14-3-3 proteins, causingFOXO1inactivation. In contrast, low nutrient and energy levels induce FOXO1 activity. AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis, partly mediates this effect through phosphorylation of Ser383 and Thr649 in FOXO1. In this study, we identified Ser22 as an additional AMPK phosphorylation site in FOXO1's N terminus, with Ser22 phosphorylation preventing binding of 14-3-3 proteins. The crystal structure of a FOXO1 peptide in complex with 14-3-3 σ at 2.3 Å resolution revealed that this is a consequence of both steric hindrance and electrostatic repulsion. Furthermore, we found that AMPK-mediated Ser22 phosphorylation impairs Thr24 phosphorylation by AKT in a hierarchical manner. Thus, numerous mechanisms maintain FOXO1 activity via AMPK signaling. AMPK-mediated Ser22 phosphorylation directly and indirectly averts binding of 14-3-3 proteins, whereas phosphorylation of Ser383 and Thr649 complementarily stimulates FOXO1 activity. Our results shed light on a mechanism that integrates inputs from both AMPK and AKT signaling pathways in a small motif to fine-tune FOXO1 transcriptional activity.
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| 7. |
- Törnroth-Horsefield, Susanna, 1973, et al.
(författare)
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Crystal Structure of AcrB in Complex with a Single Transmembrane Subunit Reveals Another Twist.
- 2007
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Ingår i: Structure (London, England : 1993). - : Elsevier BV. - 0969-2126 .- 1878-4186. ; 15:12, s. 1663-73
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial drug resistance is a serious concern for human health. Multidrug efflux pumps export a broad variety of substrates out of the cell and thereby convey resistance to the host. In Escherichia coli, the AcrB:AcrA:TolC efflux complex forms a principal transporter for which structures of the individual component proteins have been determined in isolation. Here, we present the X-ray structure of AcrB in complex with a single transmembrane protein, assigned by mass spectrometry as YajC. A specific rotation of the periplasmic porter domain of AcrB is also revealed, consistent with the hypothesized "twist-to-open" mechanism for TolC activation. Growth experiments with yajc-deleted E. coli reveal a modest increase in the organism's susceptibility to beta-lactam antibiotics, but this effect could not conclusively be attributed to the loss of interactions between YajC and AcrB.
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| 8. |
- Wadsten, Pia, 1969, et al.
(författare)
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Lipidic sponge phase crystallization of membrane proteins.
- 2006
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Ingår i: Journal of molecular biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 364:1, s. 44-53
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Tidskriftsartikel (refereegranskat)abstract
- Bicontinuous lipidic cubic phases can be used as a host for growing crystals of membrane proteins. Since the cubic phase is stiff, handling is difficult and time-consuming. Moreover, the conventional cubic phase may interfere with the hydrophilic domains of membrane proteins due to the limited size of the aqueous pores. Here, we introduce a new crystallization method that makes use of a liquid analogue of the cubic phase, the sponge phase. This phase facilitates a considerable increase in the allowed size of aqueous domains of membrane proteins, and is easily generalised to a conventional vapour diffusion crystallisation experiment, including the use of nanoliter drop crystallization robots. The appearance of the sponge phase was confirmed by visual inspection, small-angle X-ray scattering and NMR spectroscopy. Crystals of the reaction centre from Rhodobacter sphaeroides were obtained by a conventional hanging-drop experiment, were harvested directly without the addition of lipase or cryoprotectant, and the structure was refined to 2.2 Angstroms resolution. In contrast to our earlier lipidic cubic phase reaction centre structure, the mobile ubiquinone could be built and refined. The practical advantages of the sponge phase make it a potent tool for crystallization of membrane proteins.
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