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Im J, Hillenaar T, Yeoh HY, Sahasrabudhe P, Mijnders M, van Willigen M, Hagos A, de Mattos E, van der Sluijs P, Braakman I. ABC-transporter CFTR folds with high fidelity through a modular, stepwise pathway. Cell Mol Life Sci 2023; 80:33. [PMID: 36609925 PMCID: PMC9825563 DOI: 10.1007/s00018-022-04671-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 11/01/2022] [Accepted: 11/28/2022] [Indexed: 01/09/2023]
Abstract
The question how proteins fold is especially pointed for large multi-domain, multi-spanning membrane proteins with complex topologies. We have uncovered the sequence of events that encompass proper folding of the ABC transporter CFTR in live cells by combining kinetic radiolabeling with protease-susceptibility assays. We found that CFTR folds in two clearly distinct stages. The first, co-translational, stage involves folding of the 2 transmembrane domains TMD1 and TMD2, plus one nucleotide-binding domain, NBD1. The second stage is a simultaneous, post-translational increase in protease resistance for both TMDs and NBD2, caused by assembly of these domains onto NBD1. Our assays probe every 2-3 residues (on average) in CFTR. This in-depth analysis at amino-acid level allows detailed analysis of domain folding and importantly also the next level: assembly of the domains into native, folded CFTR. Defects and changes brought about by medicines, chaperones, or mutations also are amenable to analysis. We here show that the well-known disease-causing mutation F508del, which established cystic fibrosis as protein-folding disease, caused co-translational misfolding of NBD1 but not TMD1 nor TMD2 in stage 1, leading to absence of stage-2 folding. Corrector drugs rescued stage 2 without rescuing NBD1. Likewise, the DxD motif in NBD1 that was identified to be required for export of CFTR from the ER we found to be required already upstream of export as CFTR mutated in this motif phenocopies F508del CFTR. The highly modular and stepwise folding process of such a large, complex protein explains the relatively high fidelity and correctability of its folding.
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Affiliation(s)
- Jisu Im
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Tamara Hillenaar
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Hui Ying Yeoh
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands ,Present Address: Center of Translational Immunology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Priyanka Sahasrabudhe
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands ,Present Address: Navigo Proteins GmbH, 06120 Halle, Germany
| | - Marjolein Mijnders
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands ,Present Address: Princess Máxima Center for Pediatric Oncology, 3584 CS Utrecht, The Netherlands
| | - Marcel van Willigen
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands ,Present Address: Julius Clinical Ltd, 3703 CD Zeist, The Netherlands
| | - Azib Hagos
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Eduardo de Mattos
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Peter van der Sluijs
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Faculty of Science, Bijvoet Centre for Biomolecular Research, Science for Life, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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2
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Jiang Y, Thienpont B, Sapuru V, Hite RK, Dittman JS, Sturgis JN, Scheuring S. Membrane-mediated protein interactions drive membrane protein organization. Nat Commun 2022; 13:7373. [PMID: 36450733 PMCID: PMC9712761 DOI: 10.1038/s41467-022-35202-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Accepted: 11/22/2022] [Indexed: 12/02/2022] Open
Abstract
The plasma membrane's main constituents, i.e., phospholipids and membrane proteins, are known to be organized in lipid-protein functional domains and supercomplexes. No active membrane-intrinsic process is known to establish membrane organization. Thus, the interplay of thermal fluctuations and the biophysical determinants of membrane-mediated protein interactions must be considered to understand membrane protein organization. Here, we used high-speed atomic force microscopy and kinetic and membrane elastic theory to investigate the behavior of a model membrane protein in oligomerization and assembly in controlled lipid environments. We find that membrane hydrophobic mismatch modulates oligomerization and assembly energetics, and 2D organization. Our experimental and theoretical frameworks reveal how membrane organization can emerge from Brownian diffusion and a minimal set of physical properties of the membrane constituents.
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Affiliation(s)
- Yining Jiang
- Biochemistry & Structural Biology, Cell & Developmental Biology, and Molecular Biology (BCMB) Program, Weill Cornell Graduate School of Biomedical Sciences, 1300 York Avenue, New York, NY 10065 USA ,grid.5386.8000000041936877XWeill Cornell Medicine, Department of Anesthesiology, 1300 York Avenue, New York, NY 10065 USA
| | - Batiste Thienpont
- grid.5399.60000 0001 2176 4817Laboratoire d’Ingénierie des Systèmes Macromoléculaires (LISM), Unité Mixte de Recherche (UMR) 7255, Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université, Marseille, France
| | - Vinay Sapuru
- grid.51462.340000 0001 2171 9952Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA ,Physiology, Biophysics, and Systems Biology (PBSB) Program, Weill Cornell Graduate School of Biomedical Sciences, 1300 York Avenue, New York, NY 10065 USA
| | - Richard K. Hite
- grid.51462.340000 0001 2171 9952Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065 USA
| | - Jeremy S. Dittman
- grid.5386.8000000041936877XWeill Cornell Medicine, Department of Biochemistry, 1300 York Avenue, New York, NY 10065 USA
| | - James N. Sturgis
- grid.5399.60000 0001 2176 4817Laboratoire d’Ingénierie des Systèmes Macromoléculaires (LISM), Unité Mixte de Recherche (UMR) 7255, Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université, Marseille, France
| | - Simon Scheuring
- grid.5386.8000000041936877XWeill Cornell Medicine, Department of Anesthesiology, 1300 York Avenue, New York, NY 10065 USA ,grid.5386.8000000041936877XWeill Cornell Medicine, Department of Physiology and Biophysics, 1300 York Avenue, New York, NY 10065 USA ,grid.5386.8000000041936877XKavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY 14853 USA
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3
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Corin K, Bowie JU. How physical forces drive the process of helical membrane protein folding. EMBO Rep 2022; 23:e53025. [PMID: 35133709 PMCID: PMC8892262 DOI: 10.15252/embr.202153025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 07/17/2021] [Accepted: 11/24/2021] [Indexed: 11/09/2022] Open
Abstract
Protein folding is a fundamental process of life with important implications throughout biology. Indeed, tens of thousands of mutations have been associated with diseases, and most of these mutations are believed to affect protein folding rather than function. Correct folding is also a key element of design. These factors have motivated decades of research on protein folding. Unfortunately, knowledge of membrane protein folding lags that of soluble proteins. This gap is partly caused by the greater technical challenges associated with membrane protein studies, but also because of additional complexities. While soluble proteins fold in a homogenous water environment, membrane proteins fold in a setting that ranges from bulk water to highly charged to apolar. Thus, the forces that drive folding vary in different regions of the protein, and this complexity needs to be incorporated into our understanding of the folding process. Here, we review our understanding of membrane protein folding biophysics. Despite the greater challenge, better model systems and new experimental techniques are starting to unravel the forces and pathways in membrane protein folding.
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Affiliation(s)
- Karolina Corin
- Department of Chemistry and BiochemistryMolecular Biology InstituteUCLA‐DOE InstituteUniversity of CaliforniaLos AngelesCAUSA
| | - James U Bowie
- Department of Chemistry and BiochemistryMolecular Biology InstituteUCLA‐DOE InstituteUniversity of CaliforniaLos AngelesCAUSA
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4
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Szczygielski J, Kopańska M, Wysocka A, Oertel J. Cerebral Microcirculation, Perivascular Unit, and Glymphatic System: Role of Aquaporin-4 as the Gatekeeper for Water Homeostasis. Front Neurol 2021; 12:767470. [PMID: 34966347 PMCID: PMC8710539 DOI: 10.3389/fneur.2021.767470] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 11/12/2021] [Indexed: 12/13/2022] Open
Abstract
In the past, water homeostasis of the brain was understood as a certain quantitative equilibrium of water content between intravascular, interstitial, and intracellular spaces governed mostly by hydrostatic effects i.e., strictly by physical laws. The recent achievements in molecular bioscience have led to substantial changes in this regard. Some new concepts elaborate the idea that all compartments involved in cerebral fluid homeostasis create a functional continuum with an active and precise regulation of fluid exchange between them rather than only serving as separate fluid receptacles with mere passive diffusion mechanisms, based on hydrostatic pressure. According to these concepts, aquaporin-4 (AQP4) plays the central role in cerebral fluid homeostasis, acting as a water channel protein. The AQP4 not only enables water permeability through the blood-brain barrier but also regulates water exchange between perivascular spaces and the rest of the glymphatic system, described as pan-cerebral fluid pathway interlacing macroscopic cerebrospinal fluid (CSF) spaces with the interstitial fluid of brain tissue. With regards to this, AQP4 makes water shift strongly dependent on active processes including changes in cerebral microcirculation and autoregulation of brain vessels capacity. In this paper, the role of the AQP4 as the gatekeeper, regulating the water exchange between intracellular space, glymphatic system (including the so-called neurovascular units), and intravascular compartment is reviewed. In addition, the new concepts of brain edema as a misbalance in water homeostasis are critically appraised based on the newly described role of AQP4 for fluid permeation. Finally, the relevance of these hypotheses for clinical conditions (including brain trauma and stroke) and for both new and old therapy concepts are analyzed.
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Affiliation(s)
- Jacek Szczygielski
- Department of Neurosurgery, Institute of Medical Sciences, University of Rzeszów, Rzeszów, Poland.,Department of Neurosurgery, Faculty of Medicine and Saarland University Medical Center, Saarland University, Homburg, Germany
| | - Marta Kopańska
- Department of Pathophysiology, Institute of Medical Sciences, University of Rzeszów, Rzeszów, Poland
| | - Anna Wysocka
- Chair of Internal Medicine and Department of Internal Medicine in Nursing, Faculty of Health Sciences, Medical University of Lublin, Lublin, Poland
| | - Joachim Oertel
- Department of Neurosurgery, Faculty of Medicine and Saarland University Medical Center, Saarland University, Homburg, Germany
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5
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Quintana JF, Field MC. Evolution, function and roles in drug sensitivity of trypanosome aquaglyceroporins. Parasitology 2021; 148:1137-1142. [PMID: 33602349 PMCID: PMC8311954 DOI: 10.1017/s0031182021000354] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/10/2021] [Accepted: 02/15/2021] [Indexed: 12/13/2022]
Abstract
Aquaglyceroporins (AQPs) are membrane proteins that function in osmoregulation and the uptake of low molecular weight solutes, in particular glycerol and urea. The AQP family is highly conserved, with two major subfamilies having arisen very early in prokaryote evolution and retained by eukaryotes. A complex evolutionary history indicates multiple lineage-specific expansions, losses and not uncommonly a complete loss. Consequently, the AQP family is highly evolvable and has been associated with significant events in life on Earth. In the African trypanosomes, a role for the AQP2 paralogue, in sensitivity to two chemotherapeutic agents, pentamidine and melarsoprol, is well established, albeit with the mechanisms for cell entry and resistance unclear until very recently. Here, we discuss AQP evolution, structure and mechanisms by which AQPs impact drug sensitivity, suggesting that AQP2 stability is highly sensitive to mutation while serving as the major uptake pathway for pentamidine.
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Affiliation(s)
- Juan F. Quintana
- Wellcome Centre for Integrative Parasitology (WCIP), Institute of Biodiversity, Animal Health and Comparative Medicine (IBAHCM), University of Glasgow, GlasgowG61 1QH, UK
| | - Mark C. Field
- School of Life Sciences, University of Dundee, DundeeDD1 5EH, UK
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, 37005Ceske Budejovice, Czech Republic
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6
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Azad AK, Raihan T, Ahmed J, Hakim A, Emon TH, Chowdhury PA. Human Aquaporins: Functional Diversity and Potential Roles in Infectious and Non-infectious Diseases. Front Genet 2021; 12:654865. [PMID: 33796134 PMCID: PMC8007926 DOI: 10.3389/fgene.2021.654865] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2021] [Accepted: 02/22/2021] [Indexed: 12/11/2022] Open
Abstract
Aquaporins (AQPs) are integral membrane proteins and found in all living organisms from bacteria to human. AQPs mainly involved in the transmembrane diffusion of water as well as various small solutes in a bidirectional manner are widely distributed in various human tissues. Human contains 13 AQPs (AQP0-AQP12) which are divided into three sub-classes namely orthodox aquaporin (AQP0, 1, 2, 4, 5, 6, and 8), aquaglyceroporin (AQP3, 7, 9, and 10) and super or unorthodox aquaporin (AQP11 and 12) based on their pore selectivity. Human AQPs are functionally diverse, which are involved in wide variety of non-infectious diseases including cancer, renal dysfunction, neurological disorder, epilepsy, skin disease, metabolic syndrome, and even cardiac diseases. However, the association of AQPs with infectious diseases has not been fully evaluated. Several studies have unveiled that AQPs can be regulated by microbial and parasitic infections that suggest their involvement in microbial pathogenesis, inflammation-associated responses and AQP-mediated cell water homeostasis. This review mainly aims to shed light on the involvement of AQPs in infectious and non-infectious diseases and potential AQPs-target modulators. Furthermore, AQP structures, tissue-specific distributions and their physiological relevance, functional diversity and regulations have been discussed. Altogether, this review would be useful for further investigation of AQPs as a potential therapeutic target for treatment of infectious as well as non-infectious diseases.
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Affiliation(s)
- Abul Kalam Azad
- Department of Genetic Engineering and Biotechnology, School of Life Sciences, Shahjalal University of Science and Technology, Sylhet, Bangladesh
| | - Topu Raihan
- Department of Genetic Engineering and Biotechnology, School of Life Sciences, Shahjalal University of Science and Technology, Sylhet, Bangladesh
| | - Jahed Ahmed
- Department of Genetic Engineering and Biotechnology, School of Life Sciences, Shahjalal University of Science and Technology, Sylhet, Bangladesh
- Louvain Institute of Biomolecular Science and Technology, Université catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Al Hakim
- Department of Genetic Engineering and Biotechnology, School of Life Sciences, Shahjalal University of Science and Technology, Sylhet, Bangladesh
| | - Tanvir Hossain Emon
- Department of Genetic Engineering and Biotechnology, School of Life Sciences, Shahjalal University of Science and Technology, Sylhet, Bangladesh
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7
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Bañó-Polo M, Martínez-Gil L, Barrera FN, Mingarro I. Insertion of Bacteriorhodopsin Helix C Variants into Biological Membranes. ACS OMEGA 2020; 5:556-560. [PMID: 31956802 PMCID: PMC6964287 DOI: 10.1021/acsomega.9b03126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 12/04/2019] [Indexed: 06/10/2023]
Abstract
A peptide corresponding to bacteriorhodopsin (bR) helix C, later named pHLIP, inserts across lipid bilayers as a monomeric α-helix at acidic pH, but is an unstructured surface-bound monomer at neutral pH. As a result of such pH-responsiveness, pHLIP targets acidic tumors and has been used as a vehicle for imaging and drug-delivery cargoes. To gain insights about the insertion of bR helix C into biological membranes, we replaced two key aspartic residues that control the topological transition from the aqueous phase into a lipid bilayer. Here, we used an in vitro transcription-translation system to study the translocon-mediated insertion of helix C-derived segments into rough microsomes. Our data provide the first quantitative biological understanding of this effect. Interestingly, replacing the aspartic residues by glutamic residues does not significantly alters the insertion propensity, while replacement by alanines promotes a transmembrane orientation. These results are consistent with mutational data obtained in synthetic liposomes by manipulating pH conditions. Our findings support the notion that the translocon facilitates topogenesis under physiological pH conditions.
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Affiliation(s)
- Manuel Bañó-Polo
- Departament
de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar
en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València. E-46100 Burjassot, Spain
| | - Luis Martínez-Gil
- Departament
de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar
en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València. E-46100 Burjassot, Spain
| | - Francisco N. Barrera
- Department
of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Ismael Mingarro
- Departament
de Bioquímica i Biologia Molecular, Estructura de Recerca Interdisciplinar
en Biotecnologia i Biomedicina (ERI BioTecMed), Universitat de València. E-46100 Burjassot, Spain
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8
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The Role of Water Homeostasis in Muscle Function and Frailty: A Review. Nutrients 2019; 11:nu11081857. [PMID: 31405072 PMCID: PMC6723611 DOI: 10.3390/nu11081857] [Citation(s) in RCA: 78] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 07/31/2019] [Accepted: 08/07/2019] [Indexed: 02/07/2023] Open
Abstract
Water, the main component of the body, is distributed in the extracellular and intracellular compartments. Water exchange between these compartments is mainly governed by osmotic pressure. Extracellular water osmolarity must remain within very narrow limits to be compatible with life. Older adults lose the thirst sensation and the ability to concentrate urine, and this favours increased extracellular osmolarity (hyperosmotic stress). This situation, in turn, leads to cell dehydration, which has severe consequences for the intracellular protein structure and function and, ultimately, results in cell damage. Moreover, the fact that water determines cell volume may act as a metabolic signal, with cell swelling acting as an anabolic signal and cell shrinkage acting as a catabolic signal. Ageing also leads to a progressive loss in muscle mass and strength. Muscle strength is the main determinant of functional capacity, and, in elderly people, depends more on muscle quality than on muscle quantity (or muscle mass). Intracellular water content in lean mass has been related to muscle strength, functional capacity, and frailty risk, and has been proposed as an indicator of muscle quality and cell hydration. This review aims to assess the role of hyperosmotic stress and cell dehydration on muscle function and frailty.
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9
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Pellowe GA, Booth PJ. Structural insight into co-translational membrane protein folding. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1862:183019. [PMID: 31302079 DOI: 10.1016/j.bbamem.2019.07.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 07/04/2019] [Accepted: 07/05/2019] [Indexed: 11/30/2022]
Abstract
Membrane protein folding studies lag behind those of water-soluble proteins due to immense difficulties of experimental study, resulting from the need to provide a hydrophobic lipid-bilayer environment when investigated in vitro. A sound understanding of folding mechanisms is important for membrane proteins as they contribute to a third of the proteome and are frequently associated with disease when mutated and/or misfolded. Membrane proteins largely consist of α-helical, hydrophobic transmembrane domains, which insert into the membrane, often using the SecYEG/Sec61 translocase system. This mini-review highlights recent advances in techniques that can further our understanding of co-translational folding and notably, the structure and insertion of nascent chains as they emerge from translating ribosomes. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.
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Affiliation(s)
- Grant A Pellowe
- Department of Chemistry, King's College London, 7 Trinity Street, SE1 1DB, London, UK
| | - Paula J Booth
- Department of Chemistry, King's College London, 7 Trinity Street, SE1 1DB, London, UK.
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10
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Long X, Huang Y, Tan H, Li Z, Zhang R, Linpeng S, Lv W, Cao Y, Li H, Liang D, Wu L. Identification of a novel MIP frameshift mutation associated with congenital cataract in a Chinese family by whole-exome sequencing and functional analysis. Eye (Lond) 2018; 32:1359-1364. [PMID: 29695758 PMCID: PMC6085365 DOI: 10.1038/s41433-018-0084-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 02/22/2018] [Accepted: 02/26/2018] [Indexed: 11/09/2022] Open
Abstract
Purpose To detect the underlying pathogenesis of congenital cataract in a four-generation Chinese family. Methods Whole-exome sequencing (WES) of family members (III:4, IV:4, and IV:6) was performed. Sanger sequencing and bioinformatics analysis were subsequently conducted. Full-length WT-MIP or K228fs-MIP fused to HA markers at the N-terminal was transfected into HeLa cells. Next, quantitative real-time PCR, western blotting and immunofluorescence confocal laser scanning were performed. Results The age of onset for nonsyndromic cataracts in male patients was by 1-year old, earlier than for female patients, who exhibited onset at adulthood. A novel c.682_683delAA (p.K228fs230X) mutation in main intrinsic protein (MIP) cosegregated with the cataract phenotype. The instability index and unfolded states for truncated MIP were predicted to increase by bioinformatics analysis. The mRNA transcription level of K228fs-MIP was reduced compared with that of WT-MIP, and K228fs-MIP protein expression was also lower than that of WT-MIP. Immunofluorescence images showed that WT-MIP principally localized to the plasma membrane, whereas the mutant protein was trapped in the cytoplasm. Conclusions Our study generated genetic and primary functional evidence for a novel c.682_683delAA mutation in MIP that expands the variant spectrum of MIP and help us better understand the molecular basis of cataract.
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Affiliation(s)
- Xigui Long
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Yanru Huang
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Hu Tan
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Zhuo Li
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Rui Zhang
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Siyuan Linpeng
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Weigang Lv
- Hunan Jiahui Genetics Hospital, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Yingxi Cao
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Haoxian Li
- Hunan Jiahui Genetics Hospital, 110 Xiangya Road, Changsha, 410078, Hunan, PR China
| | - Desheng Liang
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China. .,Hunan Jiahui Genetics Hospital, 110 Xiangya Road, Changsha, 410078, Hunan, PR China.
| | - Lingqian Wu
- Center for Medical Genetics, School of Life Sciences, Central South University, 110 Xiangya Road, Changsha, 410078, Hunan, PR China. .,Hunan Jiahui Genetics Hospital, 110 Xiangya Road, Changsha, 410078, Hunan, PR China.
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11
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Guerriero CJ, Reutter KR, Augustine AA, Preston GM, Weiberth KF, Mackie TD, Cleveland-Rubeor HC, Bethel NP, Callenberg KM, Nakatsukasa K, Grabe M, Brodsky JL. Transmembrane helix hydrophobicity is an energetic barrier during the retrotranslocation of integral membrane ERAD substrates. Mol Biol Cell 2017; 28:2076-2090. [PMID: 28539401 PMCID: PMC5509421 DOI: 10.1091/mbc.e17-03-0184] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 05/12/2017] [Accepted: 05/16/2017] [Indexed: 12/25/2022] Open
Abstract
Integral membrane proteins fold inefficiently and are susceptible to turnover via the endoplasmic reticulum-associated degradation (ERAD) pathway. During ERAD, misfolded proteins are recognized by molecular chaperones, polyubiquitinated, and retrotranslocated to the cytoplasm for proteasomal degradation. Although many aspects of this pathway are defined, how transmembrane helices (TMHs) are removed from the membrane and into the cytoplasm before degradation is poorly understood. In this study, we asked whether the hydrophobic character of a TMH acts as an energetic barrier to retrotranslocation. To this end, we designed a dual-pass model ERAD substrate, Chimera A*, which contains the cytoplasmic misfolded domain from a characterized ERAD substrate, Sterile 6* (Ste6p*). We found that the degradation requirements for Chimera A* and Ste6p* are similar, but Chimera A* was retrotranslocated more efficiently than Ste6p* in an in vitro assay in which retrotranslocation can be quantified. We then constructed a series of Chimera A* variants containing synthetic TMHs with a range of ΔG values for membrane insertion. TMH hydrophobicity correlated inversely with retrotranslocation efficiency, and in all cases, retrotranslocation remained Cdc48p dependent. These findings provide insight into the energetic restrictions on the retrotranslocation reaction, as well as a new computational approach to predict retrotranslocation efficiency.
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Affiliation(s)
| | - Karl-Richard Reutter
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Andrew A Augustine
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - G Michael Preston
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Kurt F Weiberth
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Timothy D Mackie
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | | | - Neville P Bethel
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, CA 94158
| | - Keith M Callenberg
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
| | - Kunio Nakatsukasa
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260.,Division of Biological Science, Graduate School of Natural Sciences, Nagoya City University, Nagoya, Aichi 467-8501, Japan
| | - Michael Grabe
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, CA 94158
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260
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12
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Lara P, Öjemalm K, Reithinger J, Holgado A, Maojun Y, Hammed A, Mattle D, Kim H, Nilsson I. Refined topology model of the STT3/Stt3 protein subunit of the oligosaccharyltransferase complex. J Biol Chem 2017; 292:11349-11360. [PMID: 28512128 DOI: 10.1074/jbc.m117.779421] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 05/10/2017] [Indexed: 01/16/2023] Open
Abstract
The oligosaccharyltransferase complex, localized in the endoplasmic reticulum (ER) of eukaryotic cells, is responsible for the N-linked glycosylation of numerous protein substrates. The membrane protein STT3 is a highly conserved part of the oligosaccharyltransferase and likely contains the active site of the complex. However, understanding the catalytic determinants of this system has been challenging, in part because of a discrepancy in the structural topology of the bacterial versus eukaryotic proteins and incomplete information about the mechanism of membrane integration. Here, we use a glycosylation mapping approach to investigate these questions. We measured the membrane integration efficiency of the mouse STT3-A and yeast Stt3p transmembrane domains (TMDs) and report a refined topology of the N-terminal half of the mouse STT3-A. Our results show that most of the STT3 TMDs are well inserted into the ER membrane on their own or in the presence of the natural flanking residues. However, for the mouse STT3-A hydrophobic domains 4 and 6 and yeast Stt3p domains 2, 3a, 3c, and 6 we measured reduced insertion efficiency into the ER membrane. Furthermore, we mapped the first half of the STT3-A protein, finding two extra hydrophobic domains between the third and the fourth TMD. This result indicates that the eukaryotic STT3 has 13 transmembrane domains, consistent with the structure of the bacterial homolog of STT3 and setting the stage for future combined efforts to interrogate this fascinating system.
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Affiliation(s)
- Patricia Lara
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Karin Öjemalm
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Johannes Reithinger
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Aurora Holgado
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - You Maojun
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Abdessalem Hammed
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Daniel Mattle
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
| | - Hyun Kim
- Department of Biological Sciences, Seoul National University, Seoul 08826, South Korea
| | - IngMarie Nilsson
- From the Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden and
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13
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Abstract
The insertion and assembly of proteins into the inner membrane of bacteria are crucial for many cellular processes, including cellular respiration, signal transduction, and ion and pH homeostasis. This process requires efficient membrane targeting and insertion of proteins into the lipid bilayer in their correct orientation and proper conformation. Playing center stage in these events are the targeting components, signal recognition particle (SRP) and the SRP receptor FtsY, as well as the insertion components, the Sec translocon and the YidC insertase. Here, we will discuss new insights provided from the recent high-resolution structures of these proteins. In addition, we will review the mechanism by which a variety of proteins with different topologies are inserted into the inner membrane of Gram-negative bacteria. Finally, we report on the energetics of this process and provide information on how membrane insertion occurs in Gram-positive bacteria and Archaea. It should be noted that most of what we know about membrane protein assembly in bacteria is based on studies conducted in Escherichia coli.
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Affiliation(s)
- Andreas Kuhn
- Institute for Microbiology and Molecular Biology, University of Hohenheim, 70599 Stuttgart, Germany
| | - Hans-Georg Koch
- Institute for Biochemistry and Molecular Biology, Faculty of Medicine, Albert-Ludwigs-University of Freiburg, 79104, Freiburg, Germany
| | - Ross E Dalbey
- Department of Chemistry, The Ohio State University, Columbus, OH 43210
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14
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Heaton NS, Moshkina N, Fenouil R, Gardner TJ, Aguirre S, Shah PS, Zhao N, Manganaro L, Hultquist JF, Noel J, Sachs D, Hamilton J, Leon PE, Chawdury A, Tripathi S, Melegari C, Campisi L, Hai R, Metreveli G, Gamarnik AV, García-Sastre A, Greenbaum B, Simon V, Fernandez-Sesma A, Krogan NJ, Mulder LCF, van Bakel H, Tortorella D, Taunton J, Palese P, Marazzi I. Targeting Viral Proteostasis Limits Influenza Virus, HIV, and Dengue Virus Infection. Immunity 2016; 44:46-58. [PMID: 26789921 DOI: 10.1016/j.immuni.2015.12.017] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 10/26/2015] [Accepted: 10/28/2015] [Indexed: 12/22/2022]
Abstract
Viruses are obligate parasites and thus require the machinery of the host cell to replicate. Inhibition of host factors co-opted during active infection is a strategy hosts use to suppress viral replication and a potential pan-antiviral therapy. To define the cellular proteins and processes required for a virus during infection is thus crucial to understanding the mechanisms of virally induced disease. In this report, we generated fully infectious tagged influenza viruses and used infection-based proteomics to identify pivotal arms of cellular signaling required for influenza virus growth and infectivity. Using mathematical modeling and genetic and pharmacologic approaches, we revealed that modulation of Sec61-mediated cotranslational translocation selectively impaired glycoprotein proteostasis of influenza as well as HIV and dengue viruses and led to inhibition of viral growth and infectivity. Thus, by studying virus-human protein-protein interactions in the context of active replication, we have identified targetable host factors for broad-spectrum antiviral therapies.
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Affiliation(s)
- Nicholas S Heaton
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Natasha Moshkina
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Romain Fenouil
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Thomas J Gardner
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Sebastian Aguirre
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Priya S Shah
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158-2140, USA
| | - Nan Zhao
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Lara Manganaro
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Judd F Hultquist
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158-2140, USA
| | - Justine Noel
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - David Sachs
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Jennifer Hamilton
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Paul E Leon
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Amit Chawdury
- Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Division of Hematology and Oncology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Department of Pathology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Shashank Tripathi
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Camilla Melegari
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Laura Campisi
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Rong Hai
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Giorgi Metreveli
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Andrea V Gamarnik
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires 1405, Argentina
| | - Adolfo García-Sastre
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Division of Infectious Diseases, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Benjamin Greenbaum
- Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Division of Hematology and Oncology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Department of Pathology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Viviana Simon
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Ana Fernandez-Sesma
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Nevan J Krogan
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158-2140, USA
| | - Lubbertus C F Mulder
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Harm van Bakel
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Domenico Tortorella
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Jack Taunton
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94158-2140, USA
| | - Peter Palese
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA
| | - Ivan Marazzi
- Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA; Global Health and Emerging Pathogens Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029-6574, USA.
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15
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Abstract
Which properties of the membrane environment are essential for the folding and oligomerization of transmembrane proteins? Because the lipids that surround membrane proteins in situ spontaneously organize into bilayers, it may seem intuitive that interactions with the bilayer provide both hydrophobic and topological constraints that help the protein to achieve a stable and functional three-dimensional structure. However, one may wonder whether folding is actually driven by the membrane environment or whether the folded state just reflects an adaptation of integral proteins to the medium in which they function. Also, apart from the overall transmembrane orientation, might the asymmetry inherent in biosynthesis processes cause proteins to fold to out-of-equilibrium, metastable topologies? Which of the features of a bilayer are essential for membrane protein folding, and which are not? To which extent do translocons dictate transmembrane topologies? Recent data show that many membrane proteins fold and oligomerize very efficiently in media that bear little similarity to a membrane, casting doubt on the essentiality of many bilayer constraints. In the following discussion, we argue that some of the features of bilayers may contribute to protein folding, stability and regulation, but they are not required for the basic three-dimensional structure to be achieved. This idea, if correct, would imply that evolution has steered membrane proteins toward an accommodation to biosynthetic pathways and a good fit into their environment, but that their folding is not driven by the latter or dictated by insertion apparatuses. In other words, the three-dimensional structure of membrane proteins is essentially determined by intramolecular interactions and not by bilayer constraints and insertion pathways. Implications are discussed.
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Affiliation(s)
- Jean-Luc Popot
- Centre National de la Recherche Scientifique/Université Paris-7 UMR 7099 , Institut de Biologie Physico-Chimique (FRC 550), 13, rue Pierre-et-Marie-Curie, F-75005 Paris, France
| | - Donald M Engelman
- Department of Molecular Biophysics and Biochemistry, Yale University , Box 208114, New Haven, Connecticut 06520-8114, United States
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16
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Abstract
In this review, we provide a brief synopsis of the evolution and functional diversity of the aquaporin gene superfamily in prokaryotic and eukaryotic organisms. Based upon the latest data, we discuss the expanding list of molecules shown to permeate the central pore of aquaporins, and the unexpected diversity of water channel genes in Archaea and Bacteria. We further provide new insight into the origin by horizontal gene transfer of plant glycerol-transporting aquaporins (NIPs), and the functional co-option and gene replacement of insect glycerol transporters. Finally, we discuss the origins of four major grades of aquaporins in Eukaryota, together with the increasing repertoires of aquaporins in vertebrates.
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Affiliation(s)
- Roderick Nigel Finn
- Department of Biology, Bergen High Technology Centre, University of Bergen, Norway; Institute of Marine Research, Nordnes, 5817 Bergen, Norway; and
| | - Joan Cerdà
- Institut de Recerca i Tecnologia Agroalimentàries (IRTA)-Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), 08003 Barcelona, Spain
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17
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Klein N, Kümmerer N, Hobernik D, Schneider D. The AQP2 mutation V71M causes nephrogenic diabetes insipidus in humans but does not impair the function of a bacterial homolog. FEBS Open Bio 2015; 5:640-6. [PMID: 26442203 PMCID: PMC4552806 DOI: 10.1016/j.fob.2015.07.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 06/30/2015] [Accepted: 07/21/2015] [Indexed: 01/26/2023] Open
Abstract
The aquaporin 2 mutation V71M causes nephrogenic diabetes insipidus in humans. Val71 is highly conserved in aqua(glycero)porins and points into the translocation pore. The V71M mutation does not impair the activity and oligomerization of a bacterial homolog.
Several point mutations have been identified in human aquaporins, but their effects on the function of the respective aquaporins are mostly enigmatic. We analyzed the impact of the aquaporin 2 mutation V71M, which causes nephrogenic diabetes insipidus in humans, on aquaporin structure and activity, using the bacterial aquaglyceroporin GlpF as a model. Importantly, the sequence and structure around the V71M mutation is highly conserved between aquaporin 2 and GlpF. The V71M mutation neither impairs substrate flux nor oligomerization of the aquaglyceroporin. Therefore, the human aquaporin 2 mutant V71M is most likely active, but cellular trafficking is probably impaired.
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Key Words
- AQP ER, endoplasmic reticulum
- AQP, aquaporin
- AVP, arginine vasopressin
- AVPR2, V2 receptor
- Activity
- Aquaporin
- GlpF
- GlpF, glycerol facilitator
- GpA, glycophorin A
- HM, half-membrane-spanning
- NDI, nephrogenic diabetes insipidus
- Nephrogenic diabetes insipidus
- Protein oligomerization
- TM, transmembrane
- wt, wild-type
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Affiliation(s)
- Noreen Klein
- Institut für Pharmazie und Biochemie, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
| | - Nadine Kümmerer
- Institut für Pharmazie und Biochemie, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
| | - Dominika Hobernik
- Institut für Pharmazie und Biochemie, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
| | - Dirk Schneider
- Institut für Pharmazie und Biochemie, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany
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18
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De Marothy MT, Elofsson A. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding. Protein Sci 2015; 24:1057-74. [PMID: 25970811 DOI: 10.1002/pro.2698] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/24/2015] [Indexed: 01/12/2023]
Abstract
Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices-implying a dynamic relationship between membrane proteins and their environment.
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Affiliation(s)
- Minttu T De Marothy
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
| | - Arne Elofsson
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
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19
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Song Z, Wang L, Liu Y, Xiao W. A novel nonsense mutation in the MIP gene linked to congenital posterior polar cataracts in a Chinese family. PLoS One 2015; 10:e0119296. [PMID: 25803033 PMCID: PMC4372439 DOI: 10.1371/journal.pone.0119296] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 01/12/2015] [Indexed: 11/19/2022] Open
Abstract
Purpose To detect the causative mutation for congenital posterior polar cataracts in a five-generation Chinese family and further explore the potential pathogenesis of this disease. Methods Coding exons, with flanking sequences of five candidate genes, were screened using direct DNA sequencing. The identified mutations were confirmed by restriction fragment length polymorphism (RFLP) analysis. A full-length wild-type or an Y219* mutant aquaporin0 (AQP0) fused with an N-terminal FLAG tag, was transfected into HEK293T cells. For co-localization studies, FLAG-WT-AQP0 and Myc-Y219*-AQP0 constructs were co-transfected. Quantitative real-time RT-PCR, western blotting and immunofluorescence studies were performed to determine protein expression levels and sub-cellular localization, respectively. Results We identified a novel nonsense mutation in MIP (c.657 C>G; p.Y219*) (major intrinsic protein gene) that segregates with congenital posterior polar cataract in a Chinese family. This mutation altered a highly conserved tyrosine to a stop codon (Y219*) within AQP0.When FLAG-WT-AQP0 and FLAG-Y219*-AQP0 expression constructs were singly transfected into HEK 293T cells, mRNA expression showed no significant difference between the wild-type and the mutant, while Y219*-AQP0 protein expression was significantly lower than that of wild-type AQP0. Wild-type AQP0 predominantly localized to the plasma membrane, while the mutated protein was abundant within the cytoplasm of HEK293T cells. However, when FLAG-WT-AQP0 andMyc-MU-AQP0were co-expressed, both proteins showed high fluorescence in the cytoplasm. Conclusions The novel nonsense mutation in the MIP gene (c.657 C>G) identified in a Chinese family may cause posterior polar cataracts. The dominant negative effect of the mutated protein on the wild-type protein interfered with the trafficking of wild-type protein to the cell membrane and both the mutant and wild-type protein were trapped in the cytoplasm. Consequently, both wild-type and mutant protein lost their function as a water channel on the cell membrane, and may result in a cataract phenotype. Our data also expands the spectrum of known MIP mutations.
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Affiliation(s)
- Zixun Song
- Department of Ophthalmology, Shengjing Hospital of China Medical University, Shenyang, Liaoning, 110004, China
| | - Lianqing Wang
- Department of Medical Genetics, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100005, P. R. China
| | - Yaping Liu
- Department of Medical Genetics, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100005, P. R. China
| | - Wei Xiao
- Department of Ophthalmology, Shengjing Hospital of China Medical University, Shenyang, Liaoning, 110004, China
- * E-mail:
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20
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Whitley P, Mingarro I. Stitching proteins into membranes, not sew simple. Biol Chem 2014; 395:1417-24. [DOI: 10.1515/hsz-2014-0205] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 07/22/2014] [Indexed: 01/24/2023]
Abstract
Abstract
Most integral membrane proteins located within the endomembrane system of eukaryotic cells are first assembled co-translationally into the endoplasmic reticulum (ER) before being sorted and trafficked to other organelles. The assembly of membrane proteins is mediated by the ER translocon, which allows passage of lumenal domains through and lateral integration of transmembrane (TM) domains into the ER membrane. It may be convenient to imagine multi-TM domain containing membrane proteins being assembled by inserting their first TM domain in the correct orientation, with subsequent TM domains inserting with alternating orientations. However a simple threading model of assembly, with sequential insertion of one TM domain into the membrane after another, does not universally stand up to scrutiny. In this article we review some of the literature illustrating the complexities of membrane protein assembly. We also present our own thoughts on aspects that we feel are poorly understood. In short we hope to convince the readers that threading of membrane proteins into membranes is ‘not sew simple’ and a topic that requires further investigation.
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21
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Pogozheva ID, Mosberg HI, Lomize AL. Life at the border: adaptation of proteins to anisotropic membrane environment. Protein Sci 2014; 23:1165-96. [PMID: 24947665 DOI: 10.1002/pro.2508] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 06/17/2014] [Accepted: 06/18/2014] [Indexed: 12/25/2022]
Abstract
This review discusses main features of transmembrane (TM) proteins which distinguish them from water-soluble proteins and allow their adaptation to the anisotropic membrane environment. We overview the structural limitations on membrane protein architecture, spatial arrangement of proteins in membranes and their intrinsic hydrophobic thickness, co-translational and post-translational folding and insertion into lipid bilayers, topogenesis, high propensity to form oligomers, and large-scale conformational transitions during membrane insertion and transport function. Special attention is paid to the polarity of TM protein surfaces described by profiles of dipolarity/polarizability and hydrogen-bonding capacity parameters that match polarity of the lipid environment. Analysis of distributions of Trp resides on surfaces of TM proteins from different biological membranes indicates that interfacial membrane regions with preferential accumulation of Trp indole rings correspond to the outer part of the lipid acyl chain region-between double bonds and carbonyl groups of lipids. These "midpolar" regions are not always symmetric in proteins from natural membranes. We also examined the hydrophobic effect that drives insertion of proteins into lipid bilayer and different free energy contributions to TM protein stability, including attractive van der Waals forces and hydrogen bonds, side-chain conformational entropy, the hydrophobic mismatch, membrane deformations, and specific protein-lipid binding.
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Affiliation(s)
- Irina D Pogozheva
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan, 48109-1065
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22
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Virkki MT, Peters C, Nilsson D, Sörensen T, Cristobal S, Wallner B, Elofsson A. The positive inside rule is stronger when followed by a transmembrane helix. J Mol Biol 2014; 426:2982-91. [PMID: 24927974 DOI: 10.1016/j.jmb.2014.06.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 06/02/2014] [Accepted: 06/03/2014] [Indexed: 11/30/2022]
Abstract
The translocon recognizes transmembrane helices with sufficient level of hydrophobicity and inserts them into the membrane. However, sometimes less hydrophobic helices are also recognized. Positive inside rule, orientational preferences of and specific interactions with neighboring helices have been shown to aid in the recognition of these helices, at least in artificial systems. To better understand how the translocon inserts marginally hydrophobic helices, we studied three naturally occurring marginally hydrophobic helices, which were previously shown to require the subsequent helix for efficient translocon recognition. We find no evidence for specific interactions when we scan all residues in the subsequent helices. Instead, we identify arginines located at the N-terminal part of the subsequent helices that are crucial for the recognition of the marginally hydrophobic transmembrane helices, indicating that the positive inside rule is important. However, in two of the constructs, these arginines do not aid in the recognition without the rest of the subsequent helix; that is, the positive inside rule alone is not sufficient. Instead, the improved recognition of marginally hydrophobic helices can here be explained as follows: the positive inside rule provides an orientational preference of the subsequent helix, which in turn allows the marginally hydrophobic helix to be inserted; that is, the effect of the positive inside rule is stronger if positively charged residues are followed by a transmembrane helix. Such a mechanism obviously cannot aid C-terminal helices, and consequently, we find that the terminal helices in multi-spanning membrane proteins are more hydrophobic than internal helices.
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Affiliation(s)
- Minttu T Virkki
- Science for Life Laboratory, Stockholm University, SE-171 21 Solna, Sweden; Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Christoph Peters
- Science for Life Laboratory, Stockholm University, SE-171 21 Solna, Sweden; Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden; Swedish e-Science Research Center (SeRC), SE-100 44 Stockholm, Sweden.
| | - Daniel Nilsson
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Therese Sörensen
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
| | - Susana Cristobal
- Department of Clinical and Experimental Medicine, Cell Biology, Faculty of Health Science, Linköping University, 581 83 Linköping, Sweden; Department of Physiology, IKERBASQUE, Basque Foundation for Science, Faculty of Medicine and Dentistry, University of the Basque Country, 48949 Leioa, Spain.
| | - Björn Wallner
- Swedish e-Science Research Center (SeRC), SE-100 44 Stockholm, Sweden; Department of Physics, Chemistry and Biology, Linköping University, 581 83 Linköping, Sweden.
| | - Arne Elofsson
- Science for Life Laboratory, Stockholm University, SE-171 21 Solna, Sweden; Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden; Swedish e-Science Research Center (SeRC), SE-100 44 Stockholm, Sweden.
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23
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Wanngren J, Lara P, Ojemalm K, Maioli S, Moradi N, Chen L, Tjernberg LO, Lundkvist J, Nilsson I, Karlström H. Changed membrane integration and catalytic site conformation are two mechanisms behind the increased Aβ42/Aβ40 ratio by presenilin 1 familial Alzheimer-linked mutations. FEBS Open Bio 2014; 4:393-406. [PMID: 24918054 PMCID: PMC4050182 DOI: 10.1016/j.fob.2014.04.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 04/16/2014] [Accepted: 04/17/2014] [Indexed: 01/11/2023] Open
Abstract
Familial Alzheimer disease (FAD) mutations affect presenilin membrane integration. The transmembrane domains around the catalytic site are vulnerable to changes. All FAD mutations cause changes in the active site of the γ-secretase complex. The FAD mutants lead to a complex processing pattern of the amyloid precursor protein.
The enzyme complex γ-secretase generates amyloid β-peptide (Aβ), a 37–43-residue peptide associated with Alzheimer disease (AD). Mutations in presenilin 1 (PS1), the catalytical subunit of γ-secretase, result in familial AD (FAD). A unifying theme among FAD mutations is an alteration in the ratio Aβ species produced (the Aβ42/Aβ40 ratio), but the molecular mechanisms responsible remain elusive. In this report we have studied the impact of several different PS1 FAD mutations on the integration of selected PS1 transmembrane domains and on PS1 active site conformation, and whether any effects translate to a particular amyloid precursor protein (APP) processing phenotype. Most mutations studied caused an increase in the Aβ42/Aβ40 ratio, but via different mechanisms. The mutations that caused a particular large increase in the Aβ42/Aβ40 ratio did also display an impaired APP intracellular domain (AICD) formation and a lower total Aβ production. Interestingly, seven mutations close to the catalytic site caused a severely impaired integration of proximal transmembrane/hydrophobic sequences into the membrane. This structural defect did not correlate to a particular APP processing phenotype. Six selected FAD mutations, all of which exhibited different APP processing profiles and impact on PS1 transmembrane domain integration, were found to display an altered active site conformation. Combined, our data suggest that FAD mutations affect the PS1 structure and active site differently, resulting in several complex APP processing phenotypes, where the most aggressive mutations in terms of increased Aβ42/Aβ40 ratio are associated with a decrease in total γ-secretase activity.
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Key Words
- AD, Alzheimer disease
- AICD, amyloid precursor protein intracellular domain
- APP, amyloid precursor protein
- Alzheimer disease
- Amyloid β-peptide
- Aβ, amyloid-β peptide
- BD8, blastocyst-derived embryonic stem cells
- Bis-Tris, 2-(bis(2-hydroxyethyl)amino)-2-(hydroxymethyl)propane-1,3-diol
- CHAPSO, 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonic acid
- CRM, column-washed dog pancreas rough microsomes
- CTF, C-terminal fragment
- ER, endoplasmic reticulum
- Endo H, endoglycosidase H
- FAD, familial AD
- FLIM/FRET, Fluorescence Lifetime Imaging/ Fluorescence Resonance Energy Transfer
- GCB, γ-secretase inhibitor coupled to biotin
- GVP, Gal4VP16
- Lep, leader peptidase
- MGD, minimal glycosylation distance
- MSD, Meso Scale Discovery
- Membrane integration
- NTF, N-terminal fragment
- PS, presenilin
- Protein structure
- RM, rough microsomes
- TMD, transmembrane domains
- WT, wild type
- γ-Secretase
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Affiliation(s)
- Johanna Wanngren
- Department of NVS, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden
| | - Patricia Lara
- Department of Biochemistry & Biophysics, Stockholm University, Stockholm, Sweden
| | - Karin Ojemalm
- Department of Biochemistry & Biophysics, Stockholm University, Stockholm, Sweden
| | - Silvia Maioli
- Department of NVS, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden
| | - Nasim Moradi
- Department of Biochemistry & Biophysics, Stockholm University, Stockholm, Sweden
| | - Lu Chen
- Department of Biochemistry & Biophysics, Stockholm University, Stockholm, Sweden
| | - Lars O Tjernberg
- Department of NVS, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden
| | | | - IngMarie Nilsson
- Department of Biochemistry & Biophysics, Stockholm University, Stockholm, Sweden
| | - Helena Karlström
- Department of NVS, Center for Alzheimer Research, Karolinska Institutet, Stockholm, Sweden
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Kim SJ, Skach WR. Mechanisms of CFTR Folding at the Endoplasmic Reticulum. Front Pharmacol 2012; 3:201. [PMID: 23248597 PMCID: PMC3521238 DOI: 10.3389/fphar.2012.00201] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 11/23/2012] [Indexed: 12/20/2022] Open
Abstract
In the past decade much has been learned about how Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) folds and misfolds as the etiologic cause of cystic fibrosis (CF). CFTR folding is complex and hierarchical, takes place in multiple cellular compartments and physical environments, and involves several large networks of folding machineries. Insertion of transmembrane (TM) segments into the endoplasmic reticulum (ER) membrane and tertiary folding of cytosolic domains begin cotranslationally as the nascent polypeptide emerges from the ribosome, whereas posttranslational folding establishes critical domain-domain contacts needed to form a physiologically stable structure. Within the membrane, N- and C-terminal TM helices are sorted into bundles that project from the cytosol to form docking sites for nucleotide binding domains, NBD1 and NBD2, which in turn form a sandwich dimer for ATP binding. While tertiary folding is required for domain assembly, proper domain assembly also reciprocally affects folding of individual domains analogous to a jig-saw puzzle wherein the structure of each interlocking piece influences its neighbors. Superimposed on this process is an elaborate proteostatic network of cellular chaperones and folding machineries that facilitate the timing and coordination of specific folding steps in and across the ER membrane. While the details of this process require further refinement, we finally have a useful framework to understand key folding defect(s) caused by ΔF508 that provides a molecular target(s) for the next generation of CFTR small molecule correctors aimed at the specific defect present in the majority of CF patients.
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Affiliation(s)
- Soo Jung Kim
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University Portland, OR, USA
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25
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Veerappan A, Cymer F, Klein N, Schneider D. The Tetrameric α-Helical Membrane Protein GlpF Unfolds via a Dimeric Folding Intermediate. Biochemistry 2011; 50:10223-30. [DOI: 10.1021/bi201266m] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Anbazhagan Veerappan
- Institut für Pharmazie
und Biochemie, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
- Institut für Biochemie
und Molekularbiologie, ZBMZ, Albert-Ludwigs-Universität, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
| | - Florian Cymer
- Institut für Pharmazie
und Biochemie, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
- Institut für Biochemie
und Molekularbiologie, ZBMZ, Albert-Ludwigs-Universität, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
| | - Noreen Klein
- Institut für Pharmazie
und Biochemie, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
| | - Dirk Schneider
- Institut für Pharmazie
und Biochemie, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 30, 55128 Mainz, Germany
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26
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Hedin LE, Illergård K, Elofsson A. An Introduction to Membrane Proteins. J Proteome Res 2011; 10:3324-31. [DOI: 10.1021/pr200145a] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Linnea E. Hedin
- Department of Biochemitry and Biophysics, Stockholm Bioinformatics Center, Center for Biomembrane Research, Science for life laboratory, Swedish E-science Research Center, Stockholm University, 106 91 Stockholm, Sweden
| | - Kristoffer Illergård
- Department of Biochemitry and Biophysics, Stockholm Bioinformatics Center, Center for Biomembrane Research, Science for life laboratory, Swedish E-science Research Center, Stockholm University, 106 91 Stockholm, Sweden
| | - Arne Elofsson
- Department of Biochemitry and Biophysics, Stockholm Bioinformatics Center, Center for Biomembrane Research, Science for life laboratory, Swedish E-science Research Center, Stockholm University, 106 91 Stockholm, Sweden
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27
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Zapater C, Chauvigné F, Norberg B, Finn RN, Cerdà J. Dual neofunctionalization of a rapidly evolving aquaporin-1 paralog resulted in constrained and relaxed traits controlling channel function during meiosis resumption in teleosts. Mol Biol Evol 2011; 28:3151-69. [PMID: 21653921 DOI: 10.1093/molbev/msr146] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The preovulatory hydration of teleost oocytes is a unique process among vertebrates. The hydration mechanism is most pronounced in marine acanthomorph teleosts that spawn pelagic (floating) eggs; however, the molecular pathway for water influx remains poorly understood. Recently, we revealed that whole-genome duplication (WGD) resulted in teleosts harboring the largest repertoire of molecular water channels in the vertebrate lineage and that a duplicated aquaporin-1 paralog is implicated in the oocyte hydration process. However, the origin and function of the aquaporin-1 paralogs remain equivocal. By integrating the molecular phylogeny with synteny and structural analyses, we show here that the teleost aqp1aa and -1ab paralogs (previously annotated as aqp1a and -1b, respectively) arose by tandem duplication rather than WGD and that the Aqp1ab C-terminus is the most rapidly evolving subdomain within the vertebrate aquaporin superfamily. The functional role of Aqp1ab was investigated in Atlantic halibut, a marine acanthomorph teleost that spawns one of the largest pelagic eggs known. We demonstrate that Aqp1ab is required for full hydration of oocytes undergoing meiotic maturation. We further show that the rapid structural divergence of the C-terminal regulatory domain causes ex vivo loss of function of halibut Aqp1ab when expressed in amphibian oocytes but not in zebrafish or native oocytes. However, by using chimeric constructs of halibut Aqp1aa and -1ab and antisera specifically raised against the C-terminus of Aqp1ab, we found that this cytoplasmic domain regulates in vivo trafficking to the microvillar portion of the oocyte plasma membrane when intraoocytic osmotic pressure is at a maximum. Interestingly, by coinjecting polyA(+) mRNA from postvitellogenic halibut follicles, ex vivo intracellular trafficking of Aqp1ab is rescued in amphibian oocytes. These data reveal that the physiological role of Aqp1ab during meiosis resumption is conserved in teleosts, but the remarkable degeneracy of the cytoplasmic domain has resulted in alternative regulation of the trafficking mechanism.
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Affiliation(s)
- Cinta Zapater
- Laboratory of Institut de Recerca i Tecnologia Agroalimentàries, Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, Barcelona, Spain
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28
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Guan XG, Su WH, Yi F, Zhang D, Hao F, Zhang HG, Liu YJ, Feng XC, Ma TH. NPA motifs play a key role in plasma membrane targeting of aquaporin-4. IUBMB Life 2010; 62:222-6. [DOI: 10.1002/iub.311] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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29
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Cymer F, Schneider D. A single glutamate residue controls the oligomerization, function, and stability of the aquaglyceroporin GlpF. Biochemistry 2010; 49:279-86. [PMID: 20000688 DOI: 10.1021/bi901660t] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Like many other alpha-helical membrane proteins, the monomeric Escherichia coli aquaglyceroporin GlpF associates within cellular membranes and forms higher-order oligomeric structures. A potential impact of the oligomeric state on the protein function remains enigmatic. We have analyzed the role of residues W42 and E43 in the oligomerization of the E. coli GlpF protein in vitro and in vivo. In contrast to W42, the polar glutamate residue at position 43 appears to be critical for oligomerization. While other polar residues can substitute for the function of E43, replacement of E43 with alanine results in a greatly reduced GlpF oligomerization propensity. The reduced interaction propensity of GlpF E43A correlates with an impaired in vivo function as well as a decreased in vivo stability. Therefore, E43 is critical for the proper oligomerization of GlpF, and protein oligomerization appears to be crucial for the channel function as well as for the in vivo stability of the protein.
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Affiliation(s)
- Florian Cymer
- Institut für Biochemie und Molekularbiologie, ZBMZ, Albert-Ludwigs-Universität Freiburg,Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
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30
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Hedin LE, Ojemalm K, Bernsel A, Hennerdal A, Illergård K, Enquist K, Kauko A, Cristobal S, von Heijne G, Lerch-Bader M, Nilsson I, Elofsson A. Membrane insertion of marginally hydrophobic transmembrane helices depends on sequence context. J Mol Biol 2009; 396:221-9. [PMID: 19931281 DOI: 10.1016/j.jmb.2009.11.036] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Revised: 11/11/2009] [Accepted: 11/13/2009] [Indexed: 11/25/2022]
Abstract
In mammalian cells, most integral membrane proteins are initially inserted into the endoplasmic reticulum membrane by the so-called Sec61 translocon. However, recent predictions suggest that many transmembrane helices (TMHs) in multispanning membrane proteins are not sufficiently hydrophobic to be recognized as such by the translocon. In this study, we have screened 16 marginally hydrophobic TMHs from membrane proteins of known three-dimensional structure. Indeed, most of these TMHs do not insert efficiently into the endoplasmic reticulum membrane by themselves. To test if loops or TMHs immediately upstream or downstream of a marginally hydrophobic helix might influence the insertion efficiency, insertion of marginally hydrophobic helices was also studied in the presence of their neighboring loops and helices. The results show that flanking loops and nearest-neighbor TMHs are sufficient to ensure the insertion of many marginally hydrophobic helices. However, for at least two of the marginally hydrophobic helices, the local interactions are not enough, indicating that post-insertional rearrangements are involved in the folding of these proteins.
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Affiliation(s)
- Linnea E Hedin
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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31
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Protein contents in biological membranes can explain abnormal solvation of charged and polar residues. Proc Natl Acad Sci U S A 2009; 106:15684-9. [PMID: 19805218 DOI: 10.1073/pnas.0905394106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transmembrane helices are generally believed to insert into membranes based on their hydrophobicity. Nevertheless, there are important exceptions where polar residues have great functional importance, for instance the S4 helix of voltage-gated ion channels. It has been shown experimentally that insertion can be accomplished by hydrophobic counterbalance, predicting an arginine insertion cost of only 2.5 kcal/mol, compared with 14.9 kcal/mol in cyclohexane. Previous simulations of pure bilayers have produced values close to the pure hydrocarbon, which has lead to spirited discussion about the experimental conditions. Here, we have performed computer simulations of models better mimicking biological membranes by explicitly including protein helices at mass fractions from 15% to 55%, as well as an actual translocon. This has a striking effect on the solvation free energy of arginine. With some polar residues present, the solvation cost comes close to experimental observation at approximately 30% mass fraction, and negligible at 40%. In the presence of a translocon in the membrane, the cost of inserting arginine next to the lateral gate can be as low as 3-5 kcal/mol. The effect is mainly due to the extra helices making it easier to retain hydration water. These results offer a possible explanation for the discrepancy between the in vivo hydrophobicity scale and computer simulations and highlight the importance of the high protein contents in membranes. Although many membrane proteins are stable in pure bilayers, such simplified models might not be sufficiently accurate for insertion of polar or charged residues in biological membranes.
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32
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Abstract
The topology of polytopic membrane proteins is determined by topogenic sequences in the protein, protein-translocon interactions, and interactions during folding within the protein and between the protein and the lipid environment. Orientation of transmembrane domains is dependent on membrane phospholipid composition during initial assembly as well as on changes in lipid composition postassembly. The membrane translocation potential of negative amino acids working in opposition to the positive-inside rule is largely dampened by the normal presence of phosphatidylethanolamine, thus explaining the dominance of positive residues as retention signals. Phosphatidylethanolamine provides the appropriate charge density that permits the membrane surface to maintain a charge balance between membrane translocation and retention signals and also allows the presence of negative residues in the cytoplasmic face of proteins for other purposes.
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Affiliation(s)
- William Dowhan
- Department of Biochemistry and Molecular Biology, University of Texas-Houston Medical School, Houston, TX 77030, USA.
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33
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Abstract
The membrane protein-folding problem can be articulated by two central questions. How is protein topology established by selective peptide transport to opposite sides of the cellular membrane? And how are transmembrane segments inserted, integrated and folded within the lipid bilayer? In eukaryotes, this process usually takes place in the endoplasmic reticulum, coincident with protein synthesis, and is facilitated by the translating ribosome and the Sec61 translocon complex (RTC). At its core, the RTC forms a dynamic pathway through which the elongating nascent polypeptide moves as it is delivered into the cytosolic, lumenal and lipid compartments. This Perspective will focus on emerging evidence that the RTC functions as a protein-folding machine that restricts conformational space by establishing transmembrane topology and yet provides a permissive environment that enables nascent transmembrane domains to efficiently progress down their folding energy landscape.
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Affiliation(s)
- William R Skach
- William R Skach is in the Department of Biochemistry & Molecular Biology, Oregon Health & Sciences University, Portland, Oregon, USA.
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34
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Pitonzo D, Yang Z, Matsumura Y, Johnson AE, Skach WR. Sequence-specific retention and regulated integration of a nascent membrane protein by the endoplasmic reticulum Sec61 translocon. Mol Biol Cell 2008; 20:685-98. [PMID: 19019984 DOI: 10.1091/mbc.e08-09-0902] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A defining feature of eukaryotic polytopic protein biogenesis involves integration, folding, and packing of hydrophobic transmembrane (TM) segments into the apolar environment of the lipid bilayer. In the endoplasmic reticulum, this process is facilitated by the Sec61 translocon. Here, we use a photocross-linking approach to examine integration intermediates derived from the ATP-binding cassette transporter cystic fibrosis transmembrane conductance regulator (CFTR) and show that the timing of translocon-mediated integration can be regulated at specific stages of synthesis. During CFTR biogenesis, the eighth TM segment exits the ribosome and enters the translocon in proximity to Sec61alpha. This interaction is initially weak, and TM8 spontaneously dissociates from the translocon when the nascent chain is released from the ribosome. Polypeptide extension by only a few residues, however, results in stable TM8-Sec61alpha photocross-links that persist after peptidyl-tRNA bond cleavage. Retention of these untethered polypeptides within the translocon requires ribosome binding and is mediated by an acidic residue, Asp924, near the center of the putative TM8 helix. Remarkably, at this stage of synthesis, nascent chain release from the translocon is also strongly inhibited by ATP depletion. These findings contrast with passive partitioning models and indicate that Sec61alpha can retain TMs and actively inhibit membrane integration in a sequence-specific and ATP-dependent manner.
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Affiliation(s)
- David Pitonzo
- Department of Biochemistry and Molecular Biology, Oregon Health and Sciences University, Portland, OR 97239, USA
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35
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Daniel CJ, Conti B, Johnson AE, Skach WR. Control of translocation through the Sec61 translocon by nascent polypeptide structure within the ribosome. J Biol Chem 2008; 283:20864-73. [PMID: 18480044 PMCID: PMC2475691 DOI: 10.1074/jbc.m803517200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Indexed: 12/21/2022] Open
Abstract
During polytopic protein biogenesis, multiple transmembrane segments (TMs) must pass through the ribosome exit tunnel and into the Sec61 translocon prior to insertion into the endoplasmic reticulum membrane. To investigate how movement of a newly synthesized TM along this integration pathway might be influenced by synthesis of a second TM, we used photocross-linking probes to detect the proximity of ribosome-bound nascent polypeptides to Sec61alpha. Probes were inserted at sequential sites within TM2 of the aquaporin-1 water channel by in vitro translation of truncated mRNAs. TM2 first contacted Sec61alpha when the probe was positioned approximately 38 residues from the ribosome peptidyltransferase center, and TM2-Sec61alpha photoadducts decreased markedly when the probe was >80 residues from the peptidyltransferase center. Unexpectedly, as nascent chain length was gradually extended, photocross-linking at multiple sites within TM2 abruptly and transiently decreased, indicating that TM2 initially entered, withdrew, and then re-entered Sec61alpha. This brief reduction in TM2 photocross-linking coincided with TM3 synthesis. Replacement of TM3 with a secretory reporter domain or introduction of proline residues into TM3 changed the TM2 cross-linking profile and this biphasic behavior. These findings demonstrate that the primary and likely secondary structure of the nascent polypeptide within the ribosome exit tunnel can influence the timing with which topogenic determinants contact, enter, and pass through the translocon.
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Affiliation(s)
- Colin J Daniel
- Department of Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, OR 97239, USA
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36
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Varadaraj K, Kumari SS, Patil R, Wax MB, Mathias RT. Functional characterization of a human aquaporin 0 mutation that leads to a congenital dominant lens cataract. Exp Eye Res 2008; 87:9-21. [PMID: 18501347 PMCID: PMC2504491 DOI: 10.1016/j.exer.2008.04.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Revised: 03/28/2008] [Accepted: 04/02/2008] [Indexed: 11/17/2022]
Abstract
The aquaporin (AQP) transmembrane proteins facilitate the movement of water across the plasma membrane. In the lens, AQP0 is expressed in fiber cells and AQP1 in the epithelium. Recently, two individuals were identified with congenital polymorphic autosomal dominant cataract, due to a single nucleotide base deletion mutation in the lens AQP0. The deletion modified the reading frame resulting in the addition of a premature stop codon. In the present study, we examined the water permeability properties, trafficking and dominant negative effects as well as cytotoxicity due to the mutant AQP0 (Delta213-AQP0) protein. The membrane water permeability (P(w)) of Delta213-AQP0 expressing oocytes (14+/-1 microm/s) was significantly lower than those expressing WT-AQP0 (25+/-3 microm/s). P(w) of water injected control oocytes was 13+/-2 microm/s. Co-expression of WT-AQP0 with Delta213-AQP0 significantly lowered the P(w) (18+/-3 microm/s) compared to WT-AQP0. With or without the EGFP tag, WT-AQP0 protein localized in the plasma membranes of oocytes and cultured cells whereas Delta213-AQP0 was retained in the ER. Forster Resonance Energy Transfer (FRET) showed that WT-AQP0 partly localized with the co-expressed Delta213-AQP0. Co-localization studies suggest that the mutant AQP0 gained its dominant function by trapping the WT-AQP0 in the ER through hetero-oligomerization. Incubating the cells with chemical chaperones, namely, TMAO and DMSO, did not correct the folding/trafficking defects. Cell death in the Delta213-AQP0 expressing cells was due to necrosis caused by the accumulation of Delta213-AQP0 protein in the ER in cytotoxic proportions. The data show that replacement of the distal end of the 6th TM domain and the C-terminal domain of AQP0 due to the deletion mutation resulted in the impairment of cell membrane P(w), localization of the mutant protein in the ER without trafficking to the plasma membrane, and cytotoxicity due to the accumulation of the mutant protein. Cataracts in patients with this mutation might have resulted from the above mentioned consequences.
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Affiliation(s)
- K Varadaraj
- Department of Physiology and Biophysics, State University of NY, Stony Brook, NY 11794-8661, USA.
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37
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Abstract
Eukaryotic polytopic membrane proteins are cotranslationally inserted into the ER membrane by a multisubunit protein-conducting channel called the Sec61 translocon. Although most major translocon components have been identified and reconstituted, their stoichiometry and functional organization remain unknown. This has led to speculative and sometimes conflicting models describing how multiple transmembrane (TM) segments might be oriented and integrated during nascent polytopic protein biogenesis. Kida et al. (see p. 1441 of this issue) shed new insight into this area by demonstrating that functional translocons exhibit a remarkable flexibility by simultaneously accommodating at least two hydrophilic translocating peptides that are separated by multiple hydrophobic TMs. These surprising findings support an expanded role for the translocon in membrane protein biogenesis and require reassessment of current views based on a single small functional pore.
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Affiliation(s)
- William R Skach
- Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97239, USA.
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38
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Buck TM, Wagner J, Grund S, Skach WR. A novel tripartite motif involved in aquaporin topogenesis, monomer folding and tetramerization. Nat Struct Mol Biol 2007; 14:762-9. [PMID: 17632520 DOI: 10.1038/nsmb1275] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2006] [Accepted: 06/22/2007] [Indexed: 12/24/2022]
Abstract
Aquaporin (AQP) folding in the endoplasmic reticulum is characterized by two distinct pathways of membrane insertion that arise from divergent residues within the second transmembrane segment. We now show that in AQP1 these residues (Asn49 and Lys51) interact with Asp185 at the C terminus of TM5 to form a polar, quaternary structural motif that influences multiple stages of folding. Asn49 and Asp185 form an intramolecular hydrogen bond needed for proper helical packing, monomer formation and function. In contrast, Lys51 interacts with Asp185 on an adjacent monomer to stabilize the AQP1 tetramer. Although these residues are unique to AQP1, they share a highly conserved architecture whose functional properties can be transferred to other family members. These findings suggest a general mechanism by which evolutionary divergence of membrane proteins can confer new functional properties via alternative folding pathways that give rise to a common final structure.
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Affiliation(s)
- Teresa M Buck
- Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, 3181 SW Sam Jackson Park Rd., Portland, Oregon 97239, USA
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