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Tran N, Oh Y, Sutherland M, Cui Q, Hong M. Cholesterol-Mediated Clustering of the HIV Fusion Protein gp41 in Lipid Bilayers. J Mol Biol 2021; 434:167345. [PMID: 34762895 DOI: 10.1016/j.jmb.2021.167345] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2021] [Revised: 10/26/2021] [Accepted: 10/31/2021] [Indexed: 11/16/2022]
Abstract
The envelope glycoprotein (Env) of the human immunodeficient virus (HIV-1) is known to cluster on the viral membrane surface to attach to target cells and cause membrane fusion for HIV-1 infection. However, the molecular structural mechanisms that drive Env clustering remain opaque. Here, we use solid-state NMR spectroscopy and molecular dynamics (MD) simulations to investigate nanometer-scale clustering of the membrane-proximal external region (MPER) and transmembrane domain (TMD) of gp41, the fusion protein component of Env. Using 19F solid-state NMR experiments of mixed fluorinated peptides, we show that MPER-TMD trimers form clusters with interdigitated MPER helices in cholesterol-containing membranes. Inter-trimer 19F-19F cross peaks, which are indicative of spatial contacts within ∼2 nm, are observed in cholesterol-rich virus-mimetic membranes but are suppressed in cholesterol-free model membranes. Water-peptide and lipid-peptide cross peaks in 2D 1H-19F correlation spectra indicate that the MPER is well embedded in model phosphocholine membranes but is more exposed to the surface of the virus-mimetic membrane. These experimental results are reproduced in coarse-grained and atomistic molecular dynamics simulations, which suggest that the effects of cholesterol on gp41 clustering is likely via indirect modulation of the MPER orientation. Cholesterol binding to the helix-turn-helix region of the MPER-TMD causes a parallel orientation of the MPER with the membrane surface, thus allowing MPERs of neighboring trimers to interact with each other to cause clustering. These solid-state NMR data and molecular dynamics simulations suggest that MPER and cholesterol cooperatively govern the clustering of gp41 trimers during virus-cell membrane fusion.
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Affiliation(s)
- Nhi Tran
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, United States
| | - Younghoon Oh
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, United States
| | - Madeleine Sutherland
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, United States
| | - Qiang Cui
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, United States; Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, United States; Department of Biomedical Engineering, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, United States.
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, United States. https://twitter.com/MeiHongLab
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Chiliveri SC, Louis JM, Ghirlando R, Bax A. Transient lipid-bound states of spike protein heptad repeats provide insights into SARS-CoV-2 membrane fusion. SCIENCE ADVANCES 2021; 7:eabk2226. [PMID: 34623907 PMCID: PMC8500521 DOI: 10.1126/sciadv.abk2226] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Entry of SARS-CoV-2 into a host cell is mediated by spike, a class I viral fusion protein responsible for merging the viral and host cell membranes. Recent studies have revealed atomic-resolution models for both the postfusion 6-helix bundle (6HB) and the prefusion state of spike. However, a mechanistic understanding of the molecular basis for the intervening structural transition, important for the design of fusion inhibitors, has remained elusive. Using nuclear magnetic resonance spectroscopy and other biophysical methods, we demonstrate the presence of α-helical, membrane-bound, intermediate states of spike’s heptad repeat (HR1 and HR2) domains that are embedded at the lipid-water interface while in a slow dynamic equilibrium with the postfusion 6HB state. These results support a model where the HR domains lower the large energy barrier associated with membrane fusion by destabilizing the host and viral membranes, while 6HB formation actively drives their fusion by forcing physical proximity.
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Affiliation(s)
- Sai Chaitanya Chiliveri
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
- Corresponding author. (S.C.C.); (A.B.)
| | - John M. Louis
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Rodolfo Ghirlando
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ad Bax
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
- Corresponding author. (S.C.C.); (A.B.)
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Piai A, Fu Q, Sharp AK, Bighi B, Brown AM, Chou JJ. NMR Model of the Entire Membrane-Interacting Region of the HIV-1 Fusion Protein and Its Perturbation of Membrane Morphology. J Am Chem Soc 2021; 143:6609-6615. [PMID: 33882664 DOI: 10.1021/jacs.1c01762] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
HIV-1 envelope glycoprotein (Env) is a transmembrane protein that mediates membrane fusion and viral entry. The membrane-interacting regions of the Env, including the membrane-proximal external region (MPER), the transmembrane domain (TMD), and the cytoplasmic tail (CT), not only are essential for fusion and Env incorporation but also can strongly influence the antigenicity of the Env. Previous studies have incrementally revealed the structures of the MPER, the TMD, and the KS-LLP2 regions of the CT. Here, we determined the NMR structure of the full-length CT using a protein fragment comprising the TMD and the CT in bicelles that mimic a lipid bilayer, and by integrating the new NMR data and those acquired previously on other gp41 fragments, we derived a model of the entire membrane-interacting region of the Env. The structure shows that the CT forms a large trimeric baseplate around the TMD trimer, and by residing in the headgroup region of the lipid bilayer, the baseplate causes severe exclusion of lipid in the cytoleaflet of the bilayer. All-atom molecular dynamics simulations showed that the overall structure of the MPER-TMD-CT can be stable in a viral membrane and that a concerted movement of the KS-LLP2 region compensates for the lipid exclusion in order to maintain both structure and membrane integrity. Our structural and simulation results provide a framework for future research to manipulate the membrane structure to modulate the antigenicity of the Env for vaccine development and for mutagenesis studies for investigating membrane fusion and Env interaction with the matrix proteins.
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Affiliation(s)
- Alessandro Piai
- 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
| | | | - Beatrice Bighi
- 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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Alderson TR, Kay LE. NMR spectroscopy captures the essential role of dynamics in regulating biomolecular function. Cell 2021; 184:577-595. [PMID: 33545034 DOI: 10.1016/j.cell.2020.12.034] [Citation(s) in RCA: 79] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 12/09/2020] [Accepted: 12/21/2020] [Indexed: 01/02/2023]
Abstract
Biomolecules are in constant motion. To understand how they function, and why malfunctions can cause disease, it is necessary to describe their three-dimensional structures in terms of dynamic conformational ensembles. Here, we demonstrate how nuclear magnetic resonance (NMR) spectroscopy provides an essential, dynamic view of structural biology that captures biomolecular motions at atomic resolution. We focus on examples that emphasize the diversity of biomolecules and biochemical applications that are amenable to NMR, such as elucidating functional dynamics in large molecular machines, characterizing transient conformations implicated in the onset of disease, and obtaining atomic-level descriptions of intrinsically disordered regions that make weak interactions involved in liquid-liquid phase separation. Finally, we discuss the pivotal role that NMR has played in driving forward our understanding of the biomolecular dynamics-function paradigm.
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Affiliation(s)
- T Reid Alderson
- Department of Biochemistry, The University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Molecular Genetics, The University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Chemistry, The University of Toronto, Toronto, ON M5S A18, Canada.
| | - Lewis E Kay
- Department of Biochemistry, The University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Molecular Genetics, The University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Chemistry, The University of Toronto, Toronto, ON M5S A18, Canada; Program in Molecular Medicine, The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada.
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Kakeshpour T, Ramanujam V, Barnes CA, Shen Y, Ying J, Bax A. A lowly populated, transient β-sheet structure in monomeric Aβ 1-42 identified by multinuclear NMR of chemical denaturation. Biophys Chem 2020; 270:106531. [PMID: 33453683 DOI: 10.1016/j.bpc.2020.106531] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 12/08/2020] [Accepted: 12/13/2020] [Indexed: 02/07/2023]
Abstract
Chemical denaturation is a well-established approach for probing the equilibrium between folded and unfolded states of proteins. We demonstrate applicability of this method to the detection of a small population of a transiently folded structural element in a system that is often considered to be intrinsically fully disordered. The 1HN, 15N, 13Cα, and 13C' chemical shifts of Aβ1-40 and Aβ1-42 peptides and their M35-oxidized variants were monitored as a function of urea concentration and compared to analogous urea titrations of synthetic pentapeptides of homologous sequence. Fitting of the chemical shift titrations yields a 10 ± 1% population for a structured element at the C-terminus of Aβ1-42 that folds with a cooperativity of m = 0.06 kcal/mol·M. The fit also yields the chemical shifts of the folded state and, using a database search, for Aβ1-42 these shifts identified an antiparallel intramolecular β-sheet for residues I32-A42, linked by a type I' β-turn at G37 and G38. The structure is destabilized by oxidation of M35. Paramagnetic relaxation rates and two previously reported weak, medium-range NOE interactions are consistent with this transient β-sheet. Introduction of the requisite A42C mutation and tagging with MTSL resulted in a small stabilization of this β-sheet. Chemical shift analysis suggests a C-terminal β-sheet may be present in Aβ1-40 too, but the turn type at G37 is not type I'. The approach to derive Transient Structure from chemical Denaturation by NMR (TSD-NMR), demonstrated here for Aβ peptides, provides a sensitive tool for identifying the presence of lowly populated, transiently ordered elements in proteins that are considered to be intrinsically disordered, and permits extraction of structural data for such elements.
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Affiliation(s)
- Tayeb Kakeshpour
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
| | - Venkat Ramanujam
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
| | - C Ashley Barnes
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
| | - Yang Shen
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
| | - Jinfa Ying
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA
| | - Ad Bax
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA.
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