1
|
Wachlmayr J, Fläschner G, Pluhackova K, Sandtner W, Siligan C, Horner A. Entropic barrier of water permeation through single-file channels. Commun Chem 2023; 6:135. [PMID: 37386127 DOI: 10.1038/s42004-023-00919-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 06/02/2023] [Indexed: 07/01/2023] Open
Abstract
Facilitated water permeation through narrow biological channels is fundamental for all forms of life. Despite its significance in health and disease as well as for biotechnological applications, the energetics of water permeation are still elusive. Gibbs free energy of activation is composed of an enthalpic and an entropic component. Whereas the enthalpic contribution is readily accessible via temperature dependent water permeability measurements, estimation of the entropic contribution requires information on the temperature dependence of the rate of water permeation. Here, we estimate, by means of accurate activation energy measurements of water permeation through Aquaporin-1 and by determining the accurate single channel permeability, the entropic barrier of water permeation through a narrow biological channel. Thereby the calculated value for [Formula: see text] = 2.01 ± 0.82 J/(mol·K) links the activation energy of 3.75 ± 0.16 kcal/mol with its efficient water conduction rate of ~1010 water molecules/second. This is a first step in understanding the energetic contributions in various biological and artificial channels exhibiting vastly different pore geometries.
Collapse
Affiliation(s)
- Johann Wachlmayr
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Gotthold Fläschner
- Department of Biosystems Science and Engineering, Eidgenössiche Technische Hochschule (ETH) Zürich, Basel, Switzerland
| | - Kristyna Pluhackova
- Stuttgart Center for Simulation Science, Cluster of Excellence EXC 2075, University of Stuttgart, Universitätsstr. 32, 70569, Stuttgart, Germany
| | - Walter Sandtner
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Schwarzspanierstr. 17A, 1090, Vienna, Austria
| | - Christine Siligan
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Andreas Horner
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria.
| |
Collapse
|
2
|
Role of membrane mimetics on biophysical EPR studies of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184138. [PMID: 36764474 DOI: 10.1016/j.bbamem.2023.184138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 02/01/2023] [Accepted: 02/03/2023] [Indexed: 02/11/2023]
Abstract
Biological membranes are essential in providing the stability of membrane proteins in a functional state. Functionally stable homogeneous sample is required for biophysical electron paramagnetic resonance (EPR) studies of membrane proteins for obtaining pertinent structural dynamics of the protein. Significant progresses have been made for the optimization of the suitable membrane environments required for biophysical EPR measurements. However, no universal membrane mimetic system is available that can solubilize all membrane proteins suitable for biophysical EPR studies while maintaining the functional integrity. Great efforts are needed to optimize the sample condition to obtain better EPR data quality of membrane proteins that can provide meaningful information on structural dynamics. In this mini-review, we will discuss important aspects of membrane mimetics for biophysical EPR measurements and current progress with some of the recent examples.
Collapse
|
3
|
Pluhackova K, Schittny V, Bürkner P, Siligan C, Horner A. Multiple pore lining residues modulate water permeability of
GlpF. Protein Sci 2022; 31:e4431. [PMID: 36173178 PMCID: PMC9490802 DOI: 10.1002/pro.4431] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 08/23/2022] [Accepted: 08/25/2022] [Indexed: 11/11/2022]
Affiliation(s)
- Kristyna Pluhackova
- Stuttgart Center for Simulation Science, Cluster of Excellence EXC 2075 University of Stuttgart Stuttgart Germany
| | - Valentin Schittny
- Department of Biosystems Science and Engineering Eidgenössische Technische Hochschule (ETH) Zurich Basel Switzerland
| | - Paul‐Christian Bürkner
- Stuttgart Center for Simulation Science, Cluster of Excellence EXC 2075 University of Stuttgart Stuttgart Germany
| | | | - Andreas Horner
- Institute of Biophysics Johannes Kepler University Linz Austria
| |
Collapse
|
4
|
Gössweiner-Mohr N, Siligan C, Pluhackova K, Umlandt L, Koefler S, Trajkovska N, Horner A. The Hidden Intricacies of Aquaporins: Remarkable Details in a Common Structural Scaffold. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2202056. [PMID: 35802902 DOI: 10.1002/smll.202202056] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Evolution turned aquaporins (AQPs) into the most efficient facilitators of passive water flow through cell membranes at no expense of solute discrimination. In spite of a plethora of solved AQP structures, many structural details remain hidden. Here, by combining extensive sequence- and structural-based analysis of a unique set of 20 non-redundant high-resolution structures and molecular dynamics simulations of four representatives, key aspects of AQP stability, gating, selectivity, pore geometry, and oligomerization, with a potential impact on channel functionality, are identified. The general view of AQPs possessing a continuous open water pore is challenged and it is depicted that AQPs' selectivity is not exclusively shaped by pore-lining residues but also by the relative arrangement of transmembrane helices. Moreover, this analysis reveals that hydrophobic interactions constitute the main determinant of protein thermal stability. Finally, a numbering scheme of the conserved AQP scaffold is established, facilitating direct comparison of, for example, disease-causing mutations and prediction of potential structural consequences. Additionally, the results pave the way for the design of optimized AQP water channels to be utilized in biotechnological applications.
Collapse
Affiliation(s)
| | - Christine Siligan
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| | - Kristyna Pluhackova
- Stuttgart Center for Simulation Science, University of Stuttgart, Cluster of Excellence EXC 2075, Universitätsstr. 32, 70569, Stuttgart, Germany
| | - Linnea Umlandt
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| | - Sabina Koefler
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| | - Natasha Trajkovska
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| | - Andreas Horner
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| |
Collapse
|
5
|
Harris NJ, Reading E, Booth PJ. Cell-Free Synthesis Strategies to Probe Co-translational Folding of Proteins Within Lipid Membranes. Methods Mol Biol 2022; 2433:273-292. [PMID: 34985751 DOI: 10.1007/978-1-0716-1998-8_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
In order to comprehend the molecular basis of transmembrane protein biogenesis, methods are required that are capable of investigating the co-translational folding of these hydrophobic proteins. Equally, in artificial cell studies, controllable methods are desirable for in situ synthesis of membrane proteins that then direct reactions in the synthetic cell membrane. Here we describe a method that exploits cell-free expression systems and tunable membrane mimetics to facilitate co-translational studies. Alteration of the lipid bilayer composition improves the efficiency of the folding system. The approach also enables membrane transport proteins to be made and inserted into artificial cell platforms such as droplet interface bilayers. Importantly, this gives a new facet to the droplet networks by enabling specific transport of molecules across the synthetic bilayer against a concentration gradient. This method also includes a protocol to pause and restart translation of membrane proteins at specified positions during their co-translational folding. This stop-start strategy provides an avenue to investigate whether the proteins fold in sequence order, or if the correct fold of N-terminal regions is reliant on the synthesis of downstream residues.
Collapse
Affiliation(s)
| | - Eamonn Reading
- Department of Chemistry, King's College London, London, UK
| | - Paula J Booth
- Department of Chemistry, King's College London, London, UK.
| |
Collapse
|
6
|
Schmüser L, Trefz M, Roeters SJ, Beckner W, Pfaendtner J, Otzen D, Woutersen S, Bonn M, Schneider D, Weidner T. Membrane Structure of Aquaporin Observed with Combined Experimental and Theoretical Sum Frequency Generation Spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:13452-13459. [PMID: 34729987 DOI: 10.1021/acs.langmuir.1c02206] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
High-resolution structural information on membrane proteins is essential for understanding cell biology and for the structure-based design of new medical drugs and drug delivery strategies. X-ray diffraction (XRD) can provide angstrom-level information about the structure of membrane proteins, yet for XRD experiments, proteins are removed from their native membrane environment, chemically stabilized, and crystallized, all of which can compromise the conformation. Here, we describe how a combination of surface-sensitive vibrational spectroscopy and molecular dynamics simulations can account for the native membrane environment. We observe the structure of a glycerol facilitator channel (GlpF), an aquaporin membrane channel finely tuned to selectively transport water and glycerol molecules across the membrane barrier. We find subtle but significant differences between the XRD structure and the inferred in situ structure of GlpF.
Collapse
Affiliation(s)
- L Schmüser
- Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
| | - M Trefz
- Department of Chemistry-Biochemistry, University of Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - S J Roeters
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - W Beckner
- Department of Chemical Engineering, University of Washington, 105 Benson Hall, Seattle, Washington 98195-1750, United States
| | - J Pfaendtner
- Department of Chemical Engineering, University of Washington, 105 Benson Hall, Seattle, Washington 98195-1750, United States
| | - D Otzen
- iNANO, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark
| | - S Woutersen
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - M Bonn
- Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
| | - D Schneider
- Department of Chemistry-Biochemistry, University of Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - T Weidner
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
- Department of Chemical Engineering, University of Washington, 105 Benson Hall, Seattle, Washington 98195-1750, United States
| |
Collapse
|
7
|
Cino EA, Borbuliak M, Hu S, Tieleman DP. Lipid distributions and transleaflet cholesterol migration near heterogeneous surfaces in asymmetric bilayers. Faraday Discuss 2021; 232:103-113. [PMID: 34549760 DOI: 10.1039/d1fd00003a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Specific and nonspecific protein-lipid interactions in cell membranes have important roles in an abundance of biological functions. We have used coarse-grained (CG) molecular dynamics (MD) simulations to assess lipid distributions and cholesterol flipping dynamics around surfaces in a model asymmetric plasma membrane containing one of six structurally distinct entities: aquaporin-1 (AQP1), the bacterial β-barrel outer membrane proteins OmpF and OmpX, the KcsA potassium channel, the WALP23 peptide and a carbon nanotube (CNT). Our findings revealed varied lipid partitioning and cholesterol flipping times around the different solutes and putative cholesterol binding sites in AQP1 and KcsA. The results suggest that protein-lipid interactions can be highly variable, and that surface-dependent lipid profiles are effectively manifested in CG simulations with the Martini force field.
Collapse
Affiliation(s)
- Elio A Cino
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada. .,Department of Biochemistry and Immunology, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil
| | - Mariia Borbuliak
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada.
| | - Shangnong Hu
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada.
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada.
| |
Collapse
|
8
|
Pluhackova K, Horner A. Native-like membrane models of E. coli polar lipid extract shed light on the importance of lipid composition complexity. BMC Biol 2021; 19:4. [PMID: 33441107 PMCID: PMC7807449 DOI: 10.1186/s12915-020-00936-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 11/27/2020] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Lipid-protein interactions stabilize protein oligomers, shape their structure, and modulate their function. Whereas in vitro experiments already account for the functional importance of lipids by using natural lipid extracts, in silico methods lack behind by embedding proteins in single component lipid bilayers. However, to accurately complement in vitro experiments with molecular details at very high spatio-temporal resolution, molecular dynamics simulations have to be performed in natural(-like) lipid environments. RESULTS To enable more accurate MD simulations, we have prepared four membrane models of E. coli polar lipid extract, a typical model organism, each at all-atom (CHARMM36) and coarse-grained (Martini3) representations. These models contain all main lipid headgroup types of the E. coli inner membrane, i.e., phosphatidylethanolamines, phosphatidylglycerols, and cardiolipins, symmetrically distributed between the membrane leaflets. The lipid tail (un)saturation and propanylation stereochemistry represent the bacterial lipid tail composition of E. coli grown at 37∘C until 3/4 of the log growth phase. The comparison of the Simple three lipid component models to the complex 14-lipid component model Avanti over a broad range of physiologically relevant temperatures revealed that the balance of lipid tail unsaturation and propanylation in different positions and inclusion of lipid tails of various length maintain realistic values for lipid mobility, membrane area compressibility, lipid ordering, lipid volume and area, and the bilayer thickness. The only Simple model that was able to satisfactory reproduce most of the structural properties of the complex Avanti model showed worse agreement of the activation energy of basal water permeation with the here performed measurements. The Martini3 models reflect extremely well both experimental and atomistic behavior of the E. coli polar lipid extract membranes. Aquaporin-1 embedded in our native(-like) membranes causes partial lipid ordering and membrane thinning in its vicinity. Moreover, aquaporin-1 attracts and temporarily binds negatively charged lipids, mainly cardiolipins, with a distinct cardiolipin binding site in the crevice at the contact site between two monomers, most probably stabilizing the tetrameric protein assembly. CONCLUSIONS The here prepared and validated membrane models of E. coli polar lipids extract revealed that lipid tail complexity, in terms of double bond and cyclopropane location and varying lipid tail length, is key to stabilize membrane properties over a broad temperature range. In addition, they build a solid basis for manifold future simulation studies on more realistic lipid membranes bridging the gap between simulations and experiments.
Collapse
Affiliation(s)
- Kristyna Pluhackova
- Department of Biosystems Science and Engineering, Eidgenössiche Technische Hochschule (ETH) Zürich, Mattenstr. 26, Basel, 4058, Switzerland.
| | - Andreas Horner
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstr. 40, Linz, 4020, Austria
| |
Collapse
|
9
|
Harris NJ, Pellowe GA, Booth PJ. Cell-free expression tools to study co-translational folding of alpha helical membrane transporters. Sci Rep 2020; 10:9125. [PMID: 32499529 PMCID: PMC7272624 DOI: 10.1038/s41598-020-66097-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 05/15/2020] [Indexed: 11/28/2022] Open
Abstract
Most helical membrane proteins fold co-translationally during unidirectional polypeptide elongation by the ribosome. Studies thus far, however, have largely focussed on refolding full-length proteins from artificially induced denatured states that are far removed from the natural co-translational process. Cell-free translation offers opportunities to remedy this deficit in folding studies and has previously been used for membrane proteins. We exploit this cell-free approach to develop tools to probe co-translational folding. We show that two transporters from the ubiquitous Major Facilitator Superfamily can successfully insert into a synthetic bilayer without the need for translocon insertase apparatus that is essential in vivo. We also assess the cooperativity of domain insertion, by expressing the individual transporter domains cell-free. Furthermore, we manipulate the cell-free reaction to pause and re-start protein synthesis at specific points in the protein sequence. We find that full-length protein can still be made when stalling after the first N terminal helix has inserted into the bilayer. However, stalling after the first three helices have exited the ribosome cannot be successfully recovered. These three helices cannot insert stably when ribosome-bound during co-translational folding, as they require insertion of downstream helices.
Collapse
Affiliation(s)
- Nicola J Harris
- King's College London, Department of Chemistry, Britannia House, 7 Trinity Street, London, SE1 1DB, UK
| | - Grant A Pellowe
- King's College London, Department of Chemistry, Britannia House, 7 Trinity Street, London, SE1 1DB, UK
| | - Paula J Booth
- King's College London, Department of Chemistry, Britannia House, 7 Trinity Street, London, SE1 1DB, UK.
| |
Collapse
|
10
|
Abstract
Aquaporins are integral membrane proteins that facilitate the diffusion of water and other small, uncharged solutes across the cellular membrane and are widely distributed in organisms from humans to bacteria. However, the characteristics of prokaryotic aquaporins remain largely unknown. We investigated the distribution and sequence characterization of aquaporins in prokaryotic organisms and summarized the transport characteristics, physiological functions, and regulatory mechanisms of prokaryotic aquaporins. Aquaporin homologues were identified in 3315 prokaryotic genomes retrieved from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, but the protein clustering pattern is not completely congruent with the phylogeny of the species that carry them. Moreover, prokaryotic aquaporins display diversified aromatic/arginine constriction region (ar/R) amino acid compositions, implying multiple functions. The typical water and glycerol transport characterization, physiological functions, and regulations have been extensively studied in Escherichia coli AqpZ and GlpF. A Streptococcus aquaporin has recently been verified to facilitate the efflux of endogenous H2O2, which not only contributes to detoxification but also to species competitiveness, improving our understanding of prokaryotic aquaporins. Furthermore, recent studies revealed novel regulatory mechanisms of prokaryotic aquaporins at post-translational level. Thus, we propose that intensive investigation on prokaryotic aquaporins would extend the functional categories and working mechanisms of these ubiquitous, intrinsic membrane proteins.
Collapse
|
11
|
Huff HC, Maroutsos D, Das A. Lipid composition and macromolecular crowding effects on CYP2J2-mediated drug metabolism in nanodiscs. Protein Sci 2019; 28:928-940. [PMID: 30861250 DOI: 10.1002/pro.3603] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 03/11/2019] [Indexed: 01/13/2023]
Abstract
Lipid composition and macromolecular crowding are key external effectors of protein activity and stability whose role varies between different proteins. Therefore, it is imperative to study their effects on individual protein function. CYP2J2 is a membrane-bound cytochrome P450 in the heart involved in the metabolism of fatty acids and xenobiotics. In order to facilitate this metabolism, cytochrome P450 reductase (CPR), transfers electrons to CYP2J2 from NADPH. Herein, we use nanodiscs to show that lipid composition of the membrane bilayer affects substrate metabolism of the CYP2J2-CPR nanodisc (ND) system. Differential effects on both NADPH oxidation and substrate metabolism by CYP2J2-CPR are dependent on the lipid composition. For instance, sphingomyelin containing nanodiscs produced more secondary substrate metabolites than discs of other lipid compositions, implying a possible conformational change leading to processive metabolism. Furthermore, we demonstrate that macromolecular crowding plays a role in the lipid-solubilized CYP2J2-CPR system by increasing the Km and decreasing the Vmax , and effect that is size-dependent. Crowding also affects the CYP2J2-CPR-ND system by decreasing both the Km and Vmax for Dextran-based macromolecular crowding agents, implying an increase in substrate affinity but a lack of metabolism. Finally, protein denaturation studies show that crowding agents destabilize CYP2J2, while the multidomain protein CPR is stabilized. Overall, these studies are the first report on the role of the surrounding lipid environment and macromolecular crowding in modulating enzymatic function of CYP2J2-CPR membrane protein system.
Collapse
Affiliation(s)
- Hannah C Huff
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Demetri Maroutsos
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Aditi Das
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.,Beckman Institute for Advanced Science and Technology, Division of Nutritional Science, Neuroscience Program, and Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.,Department of Comparative Biosciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| |
Collapse
|
12
|
Lipids modulate the insertion and folding of the nascent chains of alpha helical membrane proteins. Biochem Soc Trans 2018; 46:1355-1366. [PMID: 30190329 DOI: 10.1042/bst20170424] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 07/18/2018] [Accepted: 07/31/2018] [Indexed: 02/08/2023]
Abstract
Membrane proteins must be inserted into a membrane and folded into their correct structure to function correctly. This insertion occurs during translation and synthesis by the ribosome for most α-helical membrane proteins. Precisely how this co-translational insertion and folding occurs, and the role played by the surrounding lipids, is still not understood. Most of the work on the influence of the lipid environment on folding and insertion has focussed on denatured, fully translated proteins, and thus does not replicate folding during unidirectional elongation of nascent chains that occurs in the cell. This review aims to highlight recent advances in elucidating lipid composition and bilayer properties optimal for insertion and folding of nascent chains in the membrane and in the assembly of oligomeric proteins.
Collapse
|
13
|
Trefz M, Keller R, Vogt M, Schneider D. The GlpF residue Trp219 is part of an amino-acid cluster crucial for aquaglyceroporin oligomerization and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:887-894. [PMID: 29069569 DOI: 10.1016/j.bbamem.2017.10.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 10/10/2017] [Accepted: 10/15/2017] [Indexed: 12/13/2022]
Abstract
The vestibule loop regions of aquaglyceroporins are involved in accumulation of glycerol inside the channel pore. Even though most loop regions do not show high sequence similarity among aquaglyceroporins, loop E is highly conserved in aquaglyceroporins, but not in members of the homologous aquaporins. Specifically, a tryptophan residue is extremely conserved within this loop. We have investigated the role of this residue (Trp219) that deeply protrudes into the protein and potentially interacts with adjacent loops, using the E. coli aqualgyeroporin GlpF as a model. Replacement of Trp219 affects the activity of GlpF and impairs the stability of the tetrameric protein. Furthermore, we have identified an amino acid cluster involving Trp219 that stabilizes the GlpF tetramer. Based on our results we propose that Trp219 is key for formation of a defined vestibule structure, which is crucial for glycerol accumulation as well as for the stability of the active GlpF tetramer.
Collapse
Affiliation(s)
- Margareta Trefz
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Rebecca Keller
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Miriam Vogt
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Dirk Schneider
- Johannes Gutenberg University, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany.
| |
Collapse
|