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Situ AJ, Ulmer TS. Comparison of Integrin αIIbβ3 Transmembrane Association in Vesicles and Bicelles. Biochemistry 2023. [PMID: 37279176 DOI: 10.1021/acs.biochem.3c00177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Membrane proteins are commonly reconstituted in membrane mimics exhibiting discontinuous lipid bilayers. In contrast, the continuous membranes of cells are conceptually best represented by large unilamellar vesicles (LUVs). Here, we compared the thermodynamic stability of the integrin αIIbβ3 transmembrane (TM) complex between vesicles and bicelles to assess the consequence of this simplification. In LUVs, we further evaluated the strength of the αIIb(G972S)-β3(V700T) interaction that corresponds to the hydrogen bond interaction postulated for β2 integrins. An upper limit of 0.9 kcal/mol was estimated for superior TM complex stabilization in LUVs relative to bicelles. Compared to the αIIbβ3 TM complex stability in LUVs of 5.6 ± 0.2 kcal/mol, this limit is modest, indicating that bicelles performed well relative to LUVs. The implementation of β3(V700T) alleviated αIIb(G972S) destabilization by 0.4 ± 0.2 kcal/mol in confirmation of relatively weak hydrogen bonding. Interestingly, the hydrogen bond adjusts the TM complex stability to a level that is not achievable by merely varying the residue corresponding to αIIb(Gly972).
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Affiliation(s)
- Alan J Situ
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
| | - Tobias S Ulmer
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
- Department of Biochemistry and Molecular Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, United States
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2
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Situ AJ, Kim J, An W, Kim C, Ulmer TS. Insight Into Pathological Integrin αIIbβ3 Activation From Safeguarding The Inactive State. J Mol Biol 2021; 433:166832. [PMID: 33539882 PMCID: PMC11025565 DOI: 10.1016/j.jmb.2021.166832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/01/2021] [Accepted: 01/12/2021] [Indexed: 11/20/2022]
Abstract
The inhibition of physiological activation pathways of the platelet adhesion receptor integrin αIIbβ3 may fail to prevent fatal thrombosis, suggesting that the receptor is at risk of activation by yet an unidentified pathway. Here, we report the discovery and characterization of a structural motif that safeguards the receptor by selectively destabilizing its inactive state. At the extracellular membrane border, an overpacked αIIb(W968)-β3(I693) contact prevents αIIb(Gly972) from optimally assembling the αIIbβ3 transmembrane complex, which maintains the inactive state. This destabilization of approximately 1.0 kcal/mol could be mitigated by hydrodynamic forces but not physiological agonists, thereby identifying hydrodynamic forces as pathological activation stimulus. As reproductive life spans are not generally limited by cardiovascular disease, it appears that the evolution of the safeguard was driven by fatal, hydrodynamic force-mediated integrin αIIbβ3 activation in the healthy cardiovascular system. The triggering of the safeguard solely by pathological stimuli achieves an effective increase of the free energy barrier between inactive and active receptor states without incurring an increased risk of bleeding. Thus, integrin αIIbβ3 has evolved an effective way to protect receptor functional states that indicates the availability of a mechanical activation pathway when hydrodynamic forces exceed physiological margins.
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Affiliation(s)
- Alan J Situ
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Jiyoon Kim
- Department of Life Sciences, Korea University, Seoul, Republic of Korea
| | - Woojin An
- Department of Biochemistry and Molecular Medicine, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA, USA
| | - Chungho Kim
- Department of Life Sciences, Korea University, Seoul, Republic of Korea.
| | - Tobias S Ulmer
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
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3
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Hutchison JM, Shih KC, Scheidt HA, Fantin SM, Parson KF, Pantelopulos GA, Harrington HR, Mittendorf KF, Qian S, Stein RA, Collier SE, Chambers MG, Katsaras J, Voehler MW, Ruotolo BT, Huster D, McFeeters RL, Straub JE, Nieh MP, Sanders CR. Bicelles Rich in both Sphingolipids and Cholesterol and Their Use in Studies of Membrane Proteins. J Am Chem Soc 2020; 142:12715-12729. [PMID: 32575981 DOI: 10.1021/jacs.0c04669] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
How the distinctive lipid composition of mammalian plasma membranes impacts membrane protein structure is largely unexplored, partly because of the dearth of isotropic model membrane systems that contain abundant sphingolipids and cholesterol. This gap is addressed by showing that sphingomyelin and cholesterol-rich (SCOR) lipid mixtures with phosphatidylcholine can be cosolubilized by n-dodecyl-β-melibioside to form bicelles. Small-angle X-ray and neutron scattering, as well as cryo-electron microscopy, demonstrate that these assemblies are stable over a wide range of conditions and exhibit the bilayered-disc morphology of ideal bicelles even at low lipid-to-detergent mole ratios. SCOR bicelles are shown to be compatible with a wide array of experimental techniques, as applied to the transmembrane human amyloid precursor C99 protein in this medium. These studies reveal an equilibrium between low-order oligomer structures that differ significantly from previous experimental structures of C99, providing an example of how ordered membranes alter membrane protein structure.
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Affiliation(s)
- James M Hutchison
- Chemical and Physical Biology Graduate Program and Center for Structural Biology, Vanderbilt University, Nashville 37240, Tennessee, United States
| | - Kuo-Chih Shih
- Polymer Program, Department of Chemical & Biomolecular Engineering, and Department of Biomedical Engineering, University of Connecticut, Storrs 06269, Connecticut, United States
| | - Holger A Scheidt
- Institute for Medical Physics and Biophysics, Leipzig University, Leipzig 16-18, 04107, Germany
| | - Sarah M Fantin
- Department of Chemistry, University of Michigan, Ann Arbor 48109, Michigan, United States
| | - Kristine F Parson
- Department of Chemistry, University of Michigan, Ann Arbor 48109, Michigan, United States
| | - George A Pantelopulos
- Department of Chemistry, Boston University, Boston 02215, Massachusetts, United States
| | - Haley R Harrington
- Center for Structural Biology and Department of Biochemistry, Vanderbilt University School of Medicine Basic Sciences, Nashville 37240, Tennessee, United States
| | - Kathleen F Mittendorf
- Center for Health Research, Kaiser Permanente, Portland 97227, Oregon, United States
| | - Shuo Qian
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge 37831, Tennessee, United States
| | - Richard A Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville37240, Tennessee, United States
| | - Scott E Collier
- Department of Translational and Applied Genomics, Center for Health Research, Kaiser Permanente Northwest, Portland 97227, Oregon, United States
| | - Melissa G Chambers
- Center for Structural Biology, Vanderbilt University, Nashville 37240, Tennessee, United States
| | - John Katsaras
- Neutron Scattering Division and Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge 37831, Tennessee, United States
| | - Markus W Voehler
- Center for Structural Biology and Department of Chemistry, Vanderbilt University, Nashville 37240, Tennessee, United States
| | - Brandon T Ruotolo
- Department of Chemistry, University of Michigan, Ann Arbor 48109, Michigan, United States
| | - Daniel Huster
- Institute for Medical Physics and Biophysics, Leipzig University, Leipzig 16-18, 04107, Germany
| | - Robert L McFeeters
- Department of Chemistry, University of Alabama, Huntsville 35899, Alabama, United States
| | - John E Straub
- Department of Chemistry, Boston University, Boston 02215, Massachusetts, United States
| | - Mu-Ping Nieh
- Polymer Program, Department of Chemical & Biomolecular Engineering, and Department of Biomedical Engineering, University of Connecticut, Storrs 06269, Connecticut, United States
| | - Charles R Sanders
- Center for Structural Biology, Department of Biochemistry, and Department of Medicine, Vanderbilt University School of Medicine, Nashville 37240, Tennessee, United States
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Bragin PE, Kuznetsov AS, Bocharova OV, Volynsky PE, Arseniev AS, Efremov RG, Mineev KS. Probing the effect of membrane contents on transmembrane protein-protein interaction using solution NMR and computer simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2486-2498. [PMID: 30279150 DOI: 10.1016/j.bbamem.2018.09.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 09/03/2018] [Accepted: 09/17/2018] [Indexed: 12/18/2022]
Abstract
The interaction between the secondary structure elements is the key process, determining the spatial structure and activity of a membrane protein. Transmembrane (TM) helix-helix interaction is known to be especially important for the function of so-called type I or bitopic membrane proteins. In the present work, we present the approach to study the helix-helix interaction in the TM domains of membrane proteins in various lipid environment using solution NMR spectroscopy and phospholipid bicelles. The technique is based on the ability of bicelles to form particles with the size, depending on the lipid/detergent ratio. To implement the approach, we report the experimental parameters of "ideal bicelle" models for four kinds of zwitterionic phospholipids, which can be also used in other structural studies. We show that size of bicelles and type of the rim-forming detergent do not affect substantially the spatial structure and stability of the model TM dimer. On the other hand, the effect of bilayer thickness on the free energy of the dimer is dramatic, while the structure of the protein is unchanged in various lipids with fatty chains having a length from 12 to 18 carbon atoms. The obtained data is analyzed using the computer simulations to find the physical origin of the observed effects.
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Affiliation(s)
- P E Bragin
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Lomonosov Moscow State University, Leninskiye Gory, 1, Moscow 119991, Russian Federation
| | - A S Kuznetsov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Moscow Institute of Physics and Technology, Institutsky per., 9, 141700 Dolgoprudnyi, Russian Federation; National Research University Higher School of Economics, Myasnitskaya ul. 20, 101000 Moscow, Russia
| | - O V Bocharova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Moscow Institute of Physics and Technology, Institutsky per., 9, 141700 Dolgoprudnyi, Russian Federation
| | - P E Volynsky
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation
| | - A S Arseniev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Moscow Institute of Physics and Technology, Institutsky per., 9, 141700 Dolgoprudnyi, Russian Federation
| | - R G Efremov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Moscow Institute of Physics and Technology, Institutsky per., 9, 141700 Dolgoprudnyi, Russian Federation; National Research University Higher School of Economics, Myasnitskaya ul. 20, 101000 Moscow, Russia
| | - K S Mineev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10, Moscow 117997, Russian Federation; Moscow Institute of Physics and Technology, Institutsky per., 9, 141700 Dolgoprudnyi, Russian Federation.
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Kot EF, Arseniev AS, Mineev KS. Behavior of Most Widely Spread Lipids in Isotropic Bicelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:8302-8313. [PMID: 29924628 DOI: 10.1021/acs.langmuir.8b01454] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Isotropic bicelles are a widely used membrane mimetic for structural studies of membrane proteins and their transmembrane domains. Simple and cheap in preparation, they contain a patch of lipid bilayer that reproduces the native environment of membrane proteins. Despite the obvious power of bicelles in reproducing the various kinds of environments, the vast majority of structural studies employ the single lipid/detergent system. On the other hand, even if the alternative bicelle composition is used, the properties of mixtures are not characterized, and the mere presence of lipid bilayer and discoidal shape of bicelle particles is not confirmed. Here we present an extensive investigation of various bicellar mixtures and describe the behavior of bicelles with lipids other than classical DMPC, namely sphingomyelins (SM), phosphatidylethanolamines (PE), phosphatidylglycerols (PG), phosphatidylserines (PS), and cholesterol. These lipids are rarely used in modern structural biology, but can help a lot in understanding the influence of the membrane composition on the properties of both integral and peripheral membrane proteins. Additionally, the ability of diheptanoylphosphatidylcholine (DH7PC) to serve as a rim-forming agent was investigated. We followed the phase transitions as revealed by 31P NMR and size of particles measured by 1H NMR diffusion as the criteria of the proper morphology and structure of bicelles. As an outcome, we state that SM exclusively, and PG/PS in mixtures with zwitterionic lipids can form small isotropic bicelles, which reproduce the key features of lipid behavior in bilayers. Mixtures, containing exclusively the anionic lipids, fail to reveal the lipid phase transition and do not follow the size predicted for the ideal bicelle particles. PE and DH7PC are the unwanted components of bicellar mixtures, and cholesterol can be added to bicelles, however, with certain precautions. In combination with our several most recent works, this study provides a practical guide for the preparation of small isotropic bicelles.
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Affiliation(s)
- E F Kot
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
| | - A S Arseniev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
| | - K S Mineev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS, str. Miklukho-Maklaya 16/10 , Moscow 117997, Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , Dolgoprudnyi 141700 , Russian Federation
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Kot EF, Goncharuk SA, Arseniev AS, Mineev KS. Phase Transitions in Small Isotropic Bicelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:3426-3437. [PMID: 29486112 DOI: 10.1021/acs.langmuir.7b03610] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Isotropic phospholipid bicelles are one of the most prospective membrane mimetics for the structural studies of membrane proteins in solution. Recent works provided an almost full set of data regarding the properties of isotropic bicelles; however, one major aspect of their behavior is still under consideration: the possible mixing between the lipid and detergent in the bilayer area. This problem may be resolved by studying the lipid phase transitions in bicelle particles. In the present work, we investigate two effects: phase transitions of bilayer lipids and temperature-induced growth of isotropic bicelles using the NMR spectroscopy. We propose an approach to study the phase transitions in isotropic bicelles based on the properties of 31P NMR spectra of bilayer-forming lipids. We show that phase transitions in small bicelles are "fractional", particles with the liquid-crystalline and gel bilayers coexist in solution at certain temperatures. We study the effects of lipid fatty chain type and demonstrate that the behavior of various lipids in bilayers is reproduced in the isotropic bicelles. We show that the temperature-induced growth of isotropic bicelles is not related directly to the phase transition but is the result of the reversible fusion of bicelle particles. In accordance with our data, rim detergents also have an impact on phase transitions: detergents that resist the temperature-induced growth provide the narrowest and most expressed transitions at higher temperatures. We demonstrate clearly that phase transitions take place even in the smallest bicelles that are applicable for structural studies of membrane proteins by solution NMR spectroscopy. This last finding, together with other data draws a thick line under the long-lasting argument about the relevance of small isotropic bicelles. We show with certainty that the small bicelles can reproduce the most fundamental property of lipid membranes: the ability to undergo phase transition.
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Affiliation(s)
- Erik F Kot
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS , str. Miklukho-Maklaya 16/10 , Moscow 117997 , Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , 141700 Dolgoprudnyi , Russian Federation
| | - Sergey A Goncharuk
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS , str. Miklukho-Maklaya 16/10 , Moscow 117997 , Russian Federation
- Lomonosov Moscow State University , Leninskiye Gory, 1 , Moscow 119991 , Russian Federation
| | - Alexander S Arseniev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS , str. Miklukho-Maklaya 16/10 , Moscow 117997 , Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , 141700 Dolgoprudnyi , Russian Federation
| | - Konstantin S Mineev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry , Russian Academy of Sciences RAS , str. Miklukho-Maklaya 16/10 , Moscow 117997 , Russian Federation
- Moscow Institute of Physics and Technology , Institutsky per., 9 , 141700 Dolgoprudnyi , Russian Federation
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Situ AJ, Kang SM, Frey BB, An W, Kim C, Ulmer TS. Membrane Anchoring of α-Helical Proteins: Role of Tryptophan. J Phys Chem B 2018; 122:1185-1194. [PMID: 29323921 PMCID: PMC11025564 DOI: 10.1021/acs.jpcb.7b11227] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The function of membrane proteins relies on a defined orientation of protein relative to lipid. In apparent correlation to protein anchoring, tryptophan residues are enriched in the lipid headgroup region. To characterize the thermodynamic and structural basis of this relationship in α-helical membrane proteins, we examined the role of three conserved tryptophans in the folding of the heterodimeric integrin αIIbβ3 transmembrane (TM) complex in phospholipid bicelles and mammalian membranes. In the homogenous lipid environment of bicelles, tryptophan was replaceable by residues of distinct polarities. The appropriate polarity was guided by the electrostatic potential of the tryptophan surrounding, suggesting that tryptophan can complement diverse environments by adjusting the orientation of its anisotropic side chain to achieve site-specific anchoring. As a sole membrane anchor, tryptophan made a contribution of 0.4 kcal/mol to TM complex stability in bicelles. In membranes, it proved more difficult to replace tryptophan even by tyrosine, indicating a superior capacity to interact with heterogeneous lipids of biological membranes. Interestingly, at intracellular TM helix ends, where integrin activation is initiated, sequence motifs that interact with lipids via opposing polarity patterns were found to restrict TM helix orientations beyond tryptophan anchoring. In contrast to bicelles, phenylalanine became the least accepted substitute in membranes, demonstrating an increased role of the hydrophobic effect. Altogether, our study implicates a wide amphiphilic range of tryptophan, membrane complexity, and the hydrophobic effect to be important factors in tryptophan membrane anchoring.
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Affiliation(s)
- Alan J Situ
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
| | - So-Min Kang
- Department of Life Sciences, Korea University , 145 Anam-Ro, Seongbuk-Gu, Seoul 136-701, South Korea
| | - Benjamin B Frey
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
| | - Woojin An
- Department of Biochemistry & Molecular Medicine and Norris Comprehensive Cancer Center, University of Southern California , Los Angeles, California 90033, United States
| | - Chungho Kim
- Department of Life Sciences, Korea University , 145 Anam-Ro, Seongbuk-Gu, Seoul 136-701, South Korea
| | - Tobias S Ulmer
- Department of Biochemistry & Molecular Medicine and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California , 1501 San Pablo Street, Los Angeles, California 90033, United States
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Piai A, Dev J, Fu Q, Chou JJ. Stability and Water Accessibility of the Trimeric Membrane Anchors of the HIV-1 Envelope Spikes. J Am Chem Soc 2017; 139:18432-18435. [PMID: 29193965 DOI: 10.1021/jacs.7b09352] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
HIV-1 envelope spike (Env) is a type I membrane protein that mediates viral entry. Recent studies showed that its transmembrane domain (TMD) forms a trimer in lipid bilayer whose structure has several peculiar features that remain difficult to explain. One is the presence of an arginine R696 in the middle of the TM helix. Additionally, the N- and C-terminal halves of the TM helix form trimeric cores of opposite nature (hydrophobic and hydrophilic, respectively). Here we determined the membrane partition and solvent accessibility of the TMD in bicelles that mimic a lipid bilayer. Solvent paramagnetic relaxation enhancement analysis showed that the R696 is indeed positioned close to the center of the bilayer, but, surprisingly, can exchange rapidly with water as indicated by hydrogen-deuterium exchange measurements. The solvent accessibility of R696 is likely mediated by the hydrophilic core, which also showed fast water exchange. In contrast, the N-terminal hydrophobic core showed extremely slow solvent exchange, suggesting the trimer formed by this region is extraordinarily stable. Our data explain how R696 is accommodated in the middle of the membrane while reporting the overall stability of the Env TMD trimer in lipid bilayer.
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Affiliation(s)
- Alessandro Piai
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - Jyoti Dev
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - Qingshan Fu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - James J Chou
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School , Boston, Massachusetts 02115, United States
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