1
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Raum HN, Modig K, Akke M, Weininger U. Proton Transfer Kinetics in Histidine Side Chains Determined by pH-Dependent Multi-Nuclear NMR Relaxation. J Am Chem Soc 2024; 146:22284-22294. [PMID: 39103163 PMCID: PMC11328173 DOI: 10.1021/jacs.4c04647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/07/2024]
Abstract
Histidine is a key amino-acid residue in proteins with unique properties engendered by its imidazole side chain that can exist in three different states: two different neutral tautomeric forms and a protonated, positively charged one with a pKa value close to physiological pH. Commonly, two or all three states coexist and interchange rapidly, enabling histidine to act as both donor and acceptor of hydrogen bonds, coordinate metal ions, and engage in acid/base catalysis. Understanding the exchange dynamics among the three states is critical for assessing histidine's mechanistic role in catalysis, where the rate of proton exchange and interconversion among tautomers might be rate limiting for turnover. Here, we determine the exchange kinetics of histidine residues with pKa values representative of the accessible range from 5 to 9 by measuring pH-dependent 15N, 13C, and 1H transverse relaxation rate constants for 5 nuclei in each imidazole. Proton exchange between the imidazole and the solvent is mediated by hydronium ions at acidic and neutral pH, whereas hydroxide mediated exchange becomes the dominant mechanism at basic pH. Proton transfer is very fast and reaches the diffusion limit for pKa values near neutral pH. We identify a direct pathway between the two tautomeric forms, likely mediated by a bridging water molecule or, in the case of high pH, hydroxide ion. For histidines with pKa 7, we determine all rate constants (lifetimes) involving protonation over the entire pH range. Our approach should enable critical insights into enzymatic acid/base catalyzed reactions involving histidines in proteins.
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Affiliation(s)
- Heiner N Raum
- Institute of Physics, Biophysics, Martin-Luther-University Halle-Wittenberg, Halle (Saale) D-06120, Germany
| | - Kristofer Modig
- Division of Biophysical Chemistry, Center for Molecular Protein Science, Department of Chemistry, Lund University, P.O. Box 124, Lund SE-22100, Sweden
| | - Mikael Akke
- Division of Biophysical Chemistry, Center for Molecular Protein Science, Department of Chemistry, Lund University, P.O. Box 124, Lund SE-22100, Sweden
| | - Ulrich Weininger
- Institute of Physics, Biophysics, Martin-Luther-University Halle-Wittenberg, Halle (Saale) D-06120, Germany
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2
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Pankratova Y, McKay MJ, Ma C, Tan H, Wang J, Hong M. Structure and dynamics of the proton-selective histidine and the gating tryptophan in an inward rectifying hybrid influenza B and A virus M2 proton channel. Phys Chem Chem Phys 2024; 26:20629-20644. [PMID: 39037444 PMCID: PMC11290064 DOI: 10.1039/d4cp01648c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2024] [Accepted: 07/15/2024] [Indexed: 07/23/2024]
Abstract
The M2 proteins of influenza A and B viruses form acid-activated proton channels that are essential for the virus lifecycle. Proton selectivity is achieved by a transmembrane (TM) histidine whereas gating is achieved by a tryptophan residue. Although this functional apparatus is conserved between AM2 and BM2 channels, AM2 conducts protons exclusively inward whereas BM2 conducts protons in either direction depending on the pH gradient. Previous studies showed that in AM2, mutations of D44 abolished inward rectification of AM2, suggesting that the tryptophan gate is destabilized. To elucidate how charged residues C-terminal to the tryptophan regulates channel gating, here we investigate the structure and dynamics of H19 and W23 in a BM2 mutant, GDR-BM2, in which three BM2 residues are mutated to the corresponding AM2 residues, S16G, G26D and H27R. Whole-cell electrophysiological data show that GDR-BM2 conducts protons with inward rectification, identical to wild-type (WT) AM2 but different from WT-BM2. Solid-state NMR 15N and 13C spectra of H19 indicate that the mutant BM2 channel contains higher populations of cationic histidine and neutral τ tautomers compared to WT-BM2 at acidic pH. Moreover, 19F NMR spectra of 5-19F-labeled W23 resolve three peaks at acidic pH, suggesting three tryptophan sidechain conformations. Comparison of these spectra with the tryptophan spectra of other M2 peptides suggests that these indole sidechain conformations arise from interactions with the C-terminal charged residues and with the N-terminal cationic histidine. Taken together, these solid-state NMR data show that inward rectification in M2 proton channels is accomplished by tryptophan interactions with charged residues on both its C-terminal and N-terminal sides. Gating of these M2 proton channels is thus accomplished by a multi-residue complex with finely tuned electrostatic and aromatic interactions.
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Affiliation(s)
- Yanina Pankratova
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA.
| | - Matthew J McKay
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA.
| | - Chunlong Ma
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, Arizona, 85721, USA
| | - Haozhou Tan
- Department of Medicinal Chemistry, Rutgers University, 160 Frelinghuysen Road, Piscataway, NJ 08854, USA
| | - Jun Wang
- Department of Medicinal Chemistry, Rutgers University, 160 Frelinghuysen Road, Piscataway, NJ 08854, USA
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA.
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3
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Yue Z, Wu J, Teng D, Wang Z, Voth GA. Activation of the influenza B M2 proton channel (BM2). BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.26.605324. [PMID: 39091734 PMCID: PMC11291123 DOI: 10.1101/2024.07.26.605324] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
Influenza B viruses have co-circulated during most seasonal flu epidemics and can cause significant human morbidity and mortality due to their rapid mutation, emerging drug resistance, and severe impact on vulnerable populations. The influenza B M2 proton channel (BM2) plays an essential role in viral replication, but the mechanisms behind its symmetric proton conductance and the involvement of a second histidine (His27) cluster remain unclear. Here we perform the membrane-enabled continuous constant-pH molecular dynamics simulations on wildtype BM2 and a key H27A mutant to explore its pH-dependent conformational switch. Simulations capture the activation as the first histidine (His19) protonates and reveal the transition at lower pH values compared to AM2 is a result of electrostatic repulsions between His19 and pre-protonated His27. Crucially, we provide an atomic-level understanding of the symmetric proton conduction by identifying pre-activating channel hydration in the C-terminal portion. This research advances our understanding of the function of BM2 function and lays the groundwork for further chemically reactive modeling of the explicit proton transport process as well as possible anti-flu drug design efforts.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Jiangbo Wu
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Da Teng
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
| | | | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, USA
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4
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Fedotova MV, Chuev GN. The Three-Dimensional Reference Interaction Site Model Approach as a Promising Tool for Studying Hydrated Viruses and Their Complexes with Ligands. Int J Mol Sci 2024; 25:3697. [PMID: 38612508 PMCID: PMC11011341 DOI: 10.3390/ijms25073697] [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: 03/09/2024] [Revised: 03/22/2024] [Accepted: 03/25/2024] [Indexed: 04/14/2024] Open
Abstract
Viruses are the most numerous biological form living in any ecosystem. Viral diseases affect not only people but also representatives of fauna and flora. The latest pandemic has shown how important it is for the scientific community to respond quickly to the challenge, including critically assessing the viral threat and developing appropriate measures to counter this threat. Scientists around the world are making enormous efforts to solve these problems. In silico methods, which allow quite rapid obtention of, in many cases, accurate information in this field, are effective tools for the description of various aspects of virus activity, including virus-host cell interactions, and, thus, can provide a molecular insight into the mechanism of virus functioning. The three-dimensional reference interaction site model (3D-RISM) seems to be one of the most effective and inexpensive methods to compute hydrated viruses, since the method allows us to provide efficient calculations of hydrated viruses, remaining all molecular details of the liquid environment and virus structure. The pandemic challenge has resulted in a fast increase in the number of 3D-RISM calculations devoted to hydrated viruses. To provide readers with a summary of this literature, we present a systematic overview of the 3D-RISM calculations, covering the period since 2010. We discuss various biophysical aspects of the 3D-RISM results and demonstrate capabilities, limitations, achievements, and prospects of the method using examples of viruses such as influenza, hepatitis, and SARS-CoV-2 viruses.
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Affiliation(s)
- Marina V. Fedotova
- G.A. Krestov Institute of Solution Chemistry, The Russian Academy of Sciences, Akademicheskaya St., 1, 153045 Ivanovo, Russia
| | - Gennady N. Chuev
- Institute of Theoretical and Experimental Biophysics, The Russian Academy of Sciences, Institutskaya St., 142290 Pushchino, Russia
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5
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Kariev AM, Green ME. Water, Protons, and the Gating of Voltage-Gated Potassium Channels. MEMBRANES 2024; 14:37. [PMID: 38392664 PMCID: PMC10890431 DOI: 10.3390/membranes14020037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/17/2024] [Accepted: 01/23/2024] [Indexed: 02/24/2024]
Abstract
Ion channels are ubiquitous throughout all forms of life. Potassium channels are even found in viruses. Every cell must communicate with its surroundings, so all cells have them, and excitable cells, in particular, especially nerve cells, depend on the behavior of these channels. Every channel must be open at the appropriate time, and only then, so that each channel opens in response to the stimulus that tells that channel to open. One set of channels, including those in nerve cells, responds to voltage. There is a standard model for the gating of these channels that has a section of the protein moving in response to the voltage. However, there is evidence that protons are moving, rather than protein. Water is critical as part of the gating process, although it is hard to see how this works in the standard model. Here, we review the extensive evidence of the importance of the role of water and protons in gating these channels. Our principal example, but by no means the only example, will be the Kv1.2 channel. Evidence comes from the effects of D2O, from mutations in the voltage sensing domain, as well as in the linker between that domain and the gate, and at the gate itself. There is additional evidence from computations, especially quantum calculations. Structural evidence comes from X-ray studies. The hydration of ions is critical in the transfer of ions in constricted spaces, such as the gate region and the pore of a channel; we will see how the structure of the hydrated ion fits with the structure of the channel. In addition, there is macroscopic evidence from osmotic experiments and streaming current measurements. The combined evidence is discussed in the context of a model that emphasizes the role of protons and water in gating these channels.
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Affiliation(s)
- Alisher M Kariev
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
| | - Michael E Green
- Department of Chemistry and Biochemistry, The City College of New York, New York, NY 10031, USA
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6
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Tekwani Movellan K, Wegstroth M, Overkamp K, Leonov A, Becker S, Andreas LB. Real-time tracking of drug binding to influenza A M2 reveals a high energy barrier. J Struct Biol X 2023; 8:100090. [PMID: 37363040 PMCID: PMC10285276 DOI: 10.1016/j.yjsbx.2023.100090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 05/18/2023] [Accepted: 06/02/2023] [Indexed: 06/28/2023] Open
Abstract
The drug Rimantadine binds to two different sites in the M2 protein from influenza A, a peripheral site and a pore site that is the primary site of efficacy. It remained enigmatic that pore binding did not occur in certain detergent micelles, and in particular incomplete binding was observed in a mixture of lipids selected to match the viral membrane. Here we show that two effects are responsible, namely changes in the protein upon pore binding that prevented detergent solubilization, and slow binding kinetics in the lipid samples. Using 55-100 kHz magic-angle spinning NMR, we characterize kinetics of drug binding in three different lipid environments: DPhPC, DPhPC with cholesterol and viral mimetic membrane lipid bilayers. Slow pharmacological binding kinetics allowed the characterization of spectral changes associated with non-specific binding to the protein periphery in the kinetically trapped pore-apo state. Resonance assignments were determined from a set of proton-detected 3D spectra. Chemical shift changes associated with functional binding in the pore of M2 were tracked in real time in order to estimate the activation energy. The binding kinetics are affected by pH and the lipid environment and in particular cholesterol. We found that the imidazole-imidazole hydrogen bond at residue histidine 37 is a stable feature of the protein across several lipid compositions. Pore binding breaks the imidazole-imidazole hydrogen bond and limits solubilization in DHPC detergent.
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7
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Paschke RR, Mohr S, Lange S, Lange A, Kozuch J. In Situ Spectroscopic Detection of Large-Scale Reorientations of Transmembrane Helices During Influenza A M2 Channel Opening. Angew Chem Int Ed Engl 2023; 62:e202309069. [PMID: 37733579 DOI: 10.1002/anie.202309069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 09/20/2023] [Accepted: 09/21/2023] [Indexed: 09/23/2023]
Abstract
Viroporins are small ion channels in membranes of enveloped viruses that play key roles during viral life cycles. To use viroporins as drug targets against viral infection requires in-depth mechanistic understanding and, with that, methods that enable investigations under in situ conditions. Here, we apply surface-enhanced infrared absorption (SEIRA) spectroscopy to Influenza A M2 reconstituted within a solid-supported membrane, to shed light on the mechanics of its viroporin function. M2 is a paradigm of pH-activated proton channels and controls the proton flux into the viral interior during viral infection. We use SEIRA to track the large-scale reorientation of M2's transmembrane α-helices in situ during pH-activated channel opening. We quantify this event as a helical tilt from 26° to 40° by correlating the experimental results with solid-state nuclear magnetic resonance-informed computational spectroscopy. This mechanical motion is impeded upon addition of the inhibitor rimantadine, giving a direct spectroscopic marker to test antiviral activity. The presented approach provides a spectroscopic tool to quantify large-scale structural changes and to track the function and inhibition of the growing number of viroporins from pathogenic viruses in future studies.
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Affiliation(s)
- Ronja Rabea Paschke
- Physics Department, Freie Universität Berlin, Experimental Molecular Biophysics, Arnimallee 14, 14195, Berlin, Germany
- Research Building SupraFAB, Freie Universität Berlin, Altensteinstr. 23a, 14195, Berlin, Germany
| | - Swantje Mohr
- Research Unit Molecular Biophysics, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Straße 10, 13125, Berlin, Germany
| | - Sascha Lange
- Research Unit Molecular Biophysics, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Straße 10, 13125, Berlin, Germany
| | - Adam Lange
- Research Unit Molecular Biophysics, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Straße 10, 13125, Berlin, Germany
- Institut für Biologie, Humboldt-Universität zu Berlin, Invalidenstraße 42, 10115, Berlin, Germany
| | - Jacek Kozuch
- Physics Department, Freie Universität Berlin, Experimental Molecular Biophysics, Arnimallee 14, 14195, Berlin, Germany
- Research Building SupraFAB, Freie Universität Berlin, Altensteinstr. 23a, 14195, Berlin, Germany
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8
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Aganovic A. pH-dependent endocytosis mechanisms for influenza A and SARS-coronavirus. Front Microbiol 2023; 14:1190463. [PMID: 37234537 PMCID: PMC10206014 DOI: 10.3389/fmicb.2023.1190463] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 04/24/2023] [Indexed: 05/28/2023] Open
Abstract
The ongoing SARS-CoV-2 pandemic and the influenza epidemics have revived the interest in understanding how these highly contagious enveloped viruses respond to alterations in the physicochemical properties of their microenvironment. By understanding the mechanisms and conditions by which viruses exploit the pH environment of the host cell during endocytosis, we can gain a better understanding of how they respond to pH-regulated anti-viral therapies but also pH-induced changes in extracellular environments. This review provides a detailed explanation of the pH-dependent viral structural changes preceding and initiating viral disassembly during endocytosis for influenza A (IAV) and SARS coronaviruses. Drawing upon extensive literature from the last few decades and latest research, I analyze and compare the circumstances in which IAV and SARS-coronavirus can undertake endocytotic pathways that are pH-dependent. While there are similarities in the pH-regulated patterns leading to fusion, the mechanisms and pH activation differ. In terms of fusion activity, the measured activation pH values for IAV, across all subtypes and species, vary between approximately 5.0 to 6.0, while SARS-coronavirus necessitates a lower pH of 6.0 or less. The main difference between the pH-dependent endocytic pathways is that the SARS-coronavirus, unlike IAV, require the presence of specific pH-sensitive enzymes (cathepsin L) during endosomal transport. Conversely, the conformational changes in the IAV virus under acidic conditions in endosomes occur due to the specific envelope glycoprotein residues and envelope protein ion channels (viroporins) getting protonated by H+ ions. Despite extensive research over several decades, comprehending the pH-triggered conformational alterations of viruses still poses a significant challenge. The precise mechanisms of protonation mechanisms of certain during endosomal transport for both viruses remain incompletely understood. In absence of evidence, further research is needed.
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9
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Kolocouris A, Arkin I, Glykos NM. A proof-of-concept study of the secondary structure of influenza A, B M2 and MERS- and SARS-CoV E transmembrane peptides using folding molecular dynamics simulations in a membrane mimetic solvent. Phys Chem Chem Phys 2022; 24:25391-25402. [PMID: 36239696 DOI: 10.1039/d2cp02881f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Here, we have carried out a proof-of-concept molecular dynamics (MD) simulation with adaptive tempering in a membrane mimetic environment to study the folding of single-pass membrane peptides. We tested the influenza A M2 viroporin, influenza B M2 viroporin, and protein E from coronaviruses MERS-Cov-2 and SARS-CoV-2 peptides with known experimental secondary structures in membrane bilayers. The two influenza-derived peptides are significantly different in the peptide sequence and secondary structure and more polar than the two coronavirus-derived peptides. Through a total of more than 50 μs of simulation time that could be accomplished in trifluoroethanol (TFE), as a membrane model, we characterized comparatively the folding behavior, helical stability, and helical propensity of these transmembrane peptides that match perfectly their experimental secondary structures, and we identified common motifs that reflect their quaternary organization and known (or not) biochemical function. We showed that BM2 is organized into two structurally distinct parts: a significantly more stable N-terminal half, and a fast-converting C-terminal half that continuously folds and unfolds between α-helical structures and non-canonical structures, which are mostly turns. In AM2, both the N-terminal half and C-terminal half are very flexible. In contrast, the two coronavirus-derived transmembrane peptides are much more stable and fast helix-formers when compared with the influenza ones. In particular, the SARS-derived peptide E appears to be the fastest and most stable helix-former of all the four viral peptides studied, with a helical structure that persists almost without disruption for the whole of its 10 μs simulation. By comparing the results with experimental observations, we benchmarked TFE in studying the conformation of membrane and hydrophobic peptides. This work provided accurate results suggesting a methodology to run long MD simulations and predict structural properties of biologically important membrane peptides.
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Affiliation(s)
- Antonios Kolocouris
- Laboratory of Medicinal Chemistry, Section of Pharmaceutical Chemistry, Department of Pharmacy, National and Kapodistrian University of Athens, Panepistimiopolis, 15771, Greece.
| | - Isaiah Arkin
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus Givat-Ram, Jerusalem, 91904, Israel
| | - Nicholas M Glykos
- Department of Molecular Biology and Genetics, Democritus University of Thrace, University Campus, Alexandroupolis, 68100, Greece.
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10
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Lazaridis T, Sepehri A. Amino acid deprotonation rates from classical force fields. J Chem Phys 2022; 157:085101. [DOI: 10.1063/5.0101960] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Acid ionization constants (pKa's) of titratable amino acid side chains have received a large amount of experimental and theoretical attention. In many situations, however, the rates of protonation and deprotonation, kon & koff, may also be important, for example in understanding the mechanism of action of proton channels or membrane proteins that couple proton transport to other processes. Protonation and deprotonation involve making and breaking of covalent bonds, which cannot be studied by classical force fields. However, environment effects on the rates should be captured by such methods. Here we present an approach for estimating deprotonation rates based on Warshel's extension of Marcus's theory of electron transfer, with input from molecular simulations. The missing bond dissociation energy is represented by a constant term determined by fitting the pKa value in solution. The statistics of the energy gap between protonated and deprotonated states is used to compute free energy curves of the two states and thus free energy barriers, from which the rate can be deduced. The method is applied to Glu, Asp, and His in bulk solution and select membrane proteins: the M2 proton channel, bacteriorhodopsin, and cytochrome c oxidase.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York, United States of America
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11
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Sutherland M, Tran N, Hong M. Clustering of tetrameric influenza M2 peptides in lipid bilayers investigated by 19F solid-state NMR. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183909. [PMID: 35276226 DOI: 10.1016/j.bbamem.2022.183909] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 02/08/2022] [Accepted: 03/05/2022] [Indexed: 11/19/2022]
Abstract
The influenza M2 protein forms a drug-targeted tetrameric proton channel to mediate virus uncoating, and carries out membrane scission to enable virus release. While the proton channel function of M2 has been extensively studied, the mechanism by which M2 catalyzes membrane scission is still not well understood. Previous fluorescence and electron microscopy studies indicated that M2 tetramers concentrate at the neck of the budding virus in the host plasma membrane. However, molecular evidence for this clustering is scarce. Here, we use 19F solid-state NMR to investigate M2 clustering in phospholipid bilayers. By mixing equimolar amounts of 4F-Phe47 labeled M2 peptide and CF3-Phe47 labeled M2 peptide and measuring F-CF3 cross peaks in 2D 19F19F correlation spectra, we show that M2 tetramers form nanometer-scale clusters in lipid bilayers. This clustering is stronger in cholesterol-containing membranes and phosphatidylethanolamine (PE) membranes than in cholesterol-free phosphatidylcholine and phosphatidylglycerol membranes. The observed correlation peaks indicate that Phe47 sidechains from different tetramers are less than ~2 nm apart. 1H19F correlation peaks between lipid chain protons and fluorinated Phe47 indicate that Phe47 is more deeply inserted into the lipid bilayer in the presence of cholesterol than in its absence, suggesting that Phe47 preferentially interacts with cholesterol. Static 31P NMR spectra indicate that M2 induces negative Gaussian curvature in the PE membrane. These results suggest that M2 tetramers cluster at cholesterol- and PE-rich regions of cell membranes to cause membrane curvature, which in turn can facilitate membrane scission in the last step of virus budding and release.
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Affiliation(s)
- Madeleine Sutherland
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America
| | - Nhi Tran
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States of America.
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12
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Wright AK, Paulino J, Cross TA. Emulating Membrane Protein Environments─How Much Lipid Is Required for a Native Structure: Influenza S31N M2. J Am Chem Soc 2022; 144:2137-2148. [PMID: 35089701 DOI: 10.1021/jacs.1c10174] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This report investigates the homotetrameric membrane protein structure of the S31N M2 protein from Influenza A virus in the presence of a high molar ratio of lipid. The structured regions of this protein include a single transmembrane helix and an amphipathic helix. Two structures of the S31N M2 conductance domain from Influenza A virus have been deposited in the Protein Data Bank (PDB). These structures present different symmetries about the channel main axis. We present new magic angle spinning and oriented sample solid-state NMR spectroscopic data for S31N M2 in liquid crystalline lipid bilayers using protein tetramer:lipid molar ratios ranging from 1:120 to 1:240. The data is consistent with an essentially 4-fold-symmetric structure very similar to the M2 WT structure that also has a single conformation for the four monomers, except at the His37 and Trp41 functional sites when characterized in samples with a high molar ratio of lipid. While detergent solubilization is well recognized today as a nonideal environment for small membrane proteins, here we discuss the influence of a high lipid to protein ratio for samples of the S31N M2 protein to stabilize an essentially 4-fold-symmetric conformation of the M2 membrane protein. While it is generally accepted that the chemical and physical properties of the native environment of membrane proteins needs to be reproduced judiciously to achieve the native protein structure, here we show that not only the character of the emulated membrane environment is important but also the abundance of the environment is important for achieving the native structure. This is a critical finding as a membrane protein spectroscopist's goal is always to generate a sample with the highest possible protein sensitivity while obtaining spectra of the native-like structure.
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Affiliation(s)
- Anna K Wright
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, United States.,National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Joana Paulino
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, United States.,National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Timothy A Cross
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, United States.,Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States.,National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
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13
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Watkins LC, DeGrado WF, Voth GA. Multiscale Simulation of an Influenza A M2 Channel Mutant Reveals Key Features of Its Markedly Different Proton Transport Behavior. J Am Chem Soc 2022; 144:769-776. [PMID: 34985907 PMCID: PMC8834648 DOI: 10.1021/jacs.1c09281] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The influenza A M2 channel, a prototype for viroporins, is an acid-activated viroporin that conducts protons across the viral membrane, a critical step in the viral life cycle. Four central His37 residues control channel activation by binding subsequent protons from the viral exterior, which opens the Trp41 gate and allows proton flux to the interior. Asp44 is essential for maintaining the Trp41 gate in a closed state at high pH, resulting in asymmetric conduction. The prevalent D44N mutant disrupts this gate and opens the C-terminal end of the channel, resulting in increased conduction and a loss of this asymmetric conduction. Here, we use extensive Multiscale Reactive Molecular Dynamics (MS-RMD) and quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations with an explicit, reactive excess proton to calculate the free energy of proton transport in this M2 mutant and to study the dynamic molecular-level behavior of D44N M2. We find that this mutation significantly lowers the barrier of His37 deprotonation in the activated state and shifts the barrier for entry to the Val27 tetrad. These free energy changes are reflected in structural shifts. Additionally, we show that the increased hydration around the His37 tetrad diminishes the effect of the His37 charge on the channel's water structure, facilitating proton transport and enabling activation from the viral interior. Altogether, this work provides key insight into the fundamental characteristics of PT in WT M2 and how the D44N mutation alters this PT mechanism, and it expands understanding of the role of emergent mutations in viroporins.
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Affiliation(s)
- Laura C. Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, 94158, United States
| | - Gregory A. Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States,Corresponding Author
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14
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Aledavood E, Selmi B, Estarellas C, Masetti M, Luque FJ. From Acid Activation Mechanisms of Proton Conduction to Design of Inhibitors of the M2 Proton Channel of Influenza A Virus. Front Mol Biosci 2022; 8:796229. [PMID: 35096969 PMCID: PMC8795881 DOI: 10.3389/fmolb.2021.796229] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Accepted: 12/24/2021] [Indexed: 11/26/2022] Open
Abstract
With an estimated 1 billion people affected across the globe, influenza is one of the most serious health concerns worldwide. Therapeutic treatments have encompassed a number of key functional viral proteins, mainly focused on the M2 proton channel and neuraminidase. This review highlights the efforts spent in targeting the M2 proton channel, which mediates the proton transport toward the interior of the viral particle as a preliminary step leading to the release of the fusion peptide in hemagglutinin and the fusion of the viral and endosomal membranes. Besides the structural and mechanistic aspects of the M2 proton channel, attention is paid to the challenges posed by the development of efficient small molecule inhibitors and the evolution toward novel ligands and scaffolds motivated by the emergence of resistant strains.
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Affiliation(s)
- Elnaz Aledavood
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
| | - Beatrice Selmi
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
| | - Carolina Estarellas
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
| | - Matteo Masetti
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum – Università di Bologna, Bologna, Italy
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
| | - F. Javier Luque
- Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Institut de Biomedicina and Institut de Química Teòrica i Computacional, University of Barcelona, Barcelona, Spain
- *Correspondence: Carolina Estarellas, ; Matteo Masetti, ; F. Javier Luque,
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15
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Zadorozhnyi R, Sarkar S, Quinn CM, Zadrozny KK, Ganser-Pornillos BK, Pornillos O, Gronenborn AM, Polenova T. Determination of Histidine Protonation States in Proteins by Fast Magic Angle Spinning NMR. Front Mol Biosci 2021; 8:767040. [PMID: 34957215 PMCID: PMC8703106 DOI: 10.3389/fmolb.2021.767040] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 10/15/2021] [Indexed: 12/29/2022] Open
Abstract
Histidine residues play important structural and functional roles in proteins, such as serving as metal-binding ligands, mediating enzyme catalysis, and modulating proton channel activity. Many of these activities are modulated by the ionization state of the imidazole ring. Here we present a fast MAS NMR approach for the determination of protonation and tautomeric states of His at frequencies of 40-62 kHz. The experiments combine 1H detection with selective magnetization inversion techniques and transferred echo double resonance (TEDOR)-based filters, in 2D heteronuclear correlation experiments. We illustrate this approach using microcrystalline assemblies of HIV-1 CACTD-SP1 protein.
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Affiliation(s)
- Roman Zadorozhnyi
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, United States
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Sucharita Sarkar
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, United States
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Caitlin M. Quinn
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, United States
| | - Kaneil K. Zadrozny
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, United States
| | - Barbie K. Ganser-Pornillos
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, United States
| | - Owen Pornillos
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, United States
| | - Angela M. Gronenborn
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Tatyana Polenova
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, United States
- Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
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16
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Movellan KT, Dervişoğlu R, Becker S, Andreas LB. Porengebundenes Wasser an der Schlüsselaminosäure Histidin‐37 in Influenza A M2. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202103955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Kumar Tekwani Movellan
- NMR-basierte Strukturbiologie Max-Planck-Institut für biophysikalische Chemie Am Faßberg 11 Göttingen 37077 Deutschland
| | - Rıza Dervişoğlu
- NMR-basierte Strukturbiologie Max-Planck-Institut für biophysikalische Chemie Am Faßberg 11 Göttingen 37077 Deutschland
| | - Stefan Becker
- NMR-basierte Strukturbiologie Max-Planck-Institut für biophysikalische Chemie Am Faßberg 11 Göttingen 37077 Deutschland
| | - Loren B. Andreas
- NMR-basierte Strukturbiologie Max-Planck-Institut für biophysikalische Chemie Am Faßberg 11 Göttingen 37077 Deutschland
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17
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Movellan KT, Dervişoğlu R, Becker S, Andreas LB. Pore-Bound Water at the Key Residue Histidine 37 in Influenza A M2. Angew Chem Int Ed Engl 2021; 60:24075-24079. [PMID: 34477305 PMCID: PMC8597138 DOI: 10.1002/anie.202103955] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 08/02/2021] [Indexed: 01/14/2023]
Abstract
Atomic details of structured water molecules are indispensable to understand the thermodynamics of important biological processes including the proton conduction mechanism of the M2 protein. Despite the expectation of structured water molecules based on crystal structures of Influenza A M2, only two water populations have been observed by NMR in reconstituted lipid bilayer samples. These are the bulk‐ and lipid‐associated water populations typically seen in membrane samples. Here, we detect a bound water molecule at a chemical shift of 11 ppm, located near the functional histidine 37 residue in the M2 conductance domain, which comprises residues 18 to 60. Combining 100 kHz magic‐angle spinning NMR, dynamic nuclear polarization and density functional theory calculations, we show that the bound water forms a hydrogen bond to the δ1 nitrogen of histidine 37.
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Affiliation(s)
- Kumar Tekwani Movellan
- NMR based Structural Biology, Max Planck Institute for biophysical Chemistry, Am Fassberg 11, Göttingen, 37077, Germany
| | - Rıza Dervişoğlu
- NMR based Structural Biology, Max Planck Institute for biophysical Chemistry, Am Fassberg 11, Göttingen, 37077, Germany
| | - Stefan Becker
- NMR based Structural Biology, Max Planck Institute for biophysical Chemistry, Am Fassberg 11, Göttingen, 37077, Germany
| | - Loren B Andreas
- NMR based Structural Biology, Max Planck Institute for biophysical Chemistry, Am Fassberg 11, Göttingen, 37077, Germany
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18
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Patni D, Jha SK. Protonation-Deprotonation Switch Controls the Amyloid-like Misfolding of Nucleic-Acid-Binding Domains of TDP-43. J Phys Chem B 2021; 125:8383-8394. [PMID: 34318672 DOI: 10.1021/acs.jpcb.1c03262] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Nutrient starvation stress acidifies the cytosol and leads to the formation of large protein assemblies and misfolded aggregates. However, how starvation stress is sensed at the molecular level and leads to protein misfolding is poorly understood. TDP-43 is a vital protein, which, under stress-like conditions, associates with stress granule proteins via its functional nucleic-acid-binding domains (TDP-43tRRM) and misfolds to form aberrant aggregates. Here, we show that the monomeric N form of TDP-43tRRM forms a misfolded amyloid-like protein assembly, β form, in a pH-dependent manner and identified the critical protein side-chain residue whose protonation triggers its misfolding. We systematically mutated the three buried ionizable residues, D105, H166, and H256, to neutral amino acids to block the pH-dependent protonation-deprotonation titration of their side chain and studied their effect on the N-to-β transition. We observed that D105A and H256Q resembled TDP-43tRRM in their pH-dependent misfolding behavior. However, H166Q retains the N-like secondary structure under low-pH conditions and does not show pH-dependent misfolding to the β form. These results indicate that H166 is the critical side-chain residue whose protonation triggers the misfolding of TDP-43tRRM and shed light on how stress-induced misfolding of proteins during neurodegeneration could begin from site-specific triggers.
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Affiliation(s)
- Divya Patni
- Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Santosh Kumar Jha
- Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
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19
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Gelenter MD, Mandala VS, Niesen MJM, Sharon DA, Dregni AJ, Willard AP, Hong M. Water orientation and dynamics in the closed and open influenza B virus M2 proton channels. Commun Biol 2021; 4:338. [PMID: 33712696 PMCID: PMC7955094 DOI: 10.1038/s42003-021-01847-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 02/11/2021] [Indexed: 01/03/2023] Open
Abstract
The influenza B M2 protein forms a water-filled tetrameric channel to conduct protons across the lipid membrane. To understand how channel water mediates proton transport, we have investigated the water orientation and dynamics using solid-state NMR spectroscopy and molecular dynamics (MD) simulations. 13C-detected water 1H NMR relaxation times indicate that water has faster rotational motion in the low-pH open channel than in the high-pH closed channel. Despite this faster dynamics, the open-channel water shows higher orientational order, as manifested by larger motionally-averaged 1H chemical shift anisotropies. MD simulations indicate that this order is induced by the cationic proton-selective histidine at low pH. Furthermore, the water network has fewer hydrogen-bonding bottlenecks in the open state than in the closed state. Thus, faster dynamics and higher orientational order of water molecules in the open channel establish the water network structure that is necessary for proton hopping.
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Affiliation(s)
- Martin D Gelenter
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Michiel J M Niesen
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Dina A Sharon
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Aurelio J Dregni
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Adam P Willard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
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20
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Mtambo SE, Amoako DG, Somboro AM, Agoni C, Lawal MM, Gumede NS, Khan RB, Kumalo HM. Influenza Viruses: Harnessing the Crucial Role of the M2 Ion-Channel and Neuraminidase toward Inhibitor Design. Molecules 2021; 26:880. [PMID: 33562349 PMCID: PMC7916051 DOI: 10.3390/molecules26040880] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Revised: 02/01/2021] [Accepted: 02/01/2021] [Indexed: 12/18/2022] Open
Abstract
As a member of the Orthomyxoviridae family of viruses, influenza viruses (IVs) are known causative agents of respiratory infection in vertebrates. They remain a major global threat responsible for the most virulent diseases and global pandemics in humans. The virulence of IVs and the consequential high morbidity and mortality of IV infections are primarily attributed to the high mutation rates in the IVs' genome coupled with the numerous genomic segments, which give rise to antiviral resistant and vaccine evading strains. Current therapeutic options include vaccines and small molecule inhibitors, which therapeutically target various catalytic processes in IVs. However, the periodic emergence of new IV strains necessitates the continuous development of novel anti-influenza therapeutic options. The crux of this review highlights the recent studies on the biology of influenza viruses, focusing on the structure, function, and mechanism of action of the M2 channel and neuraminidase as therapeutic targets. We further provide an update on the development of new M2 channel and neuraminidase inhibitors as an alternative to existing anti-influenza therapy. We conclude by highlighting therapeutic strategies that could be explored further towards the design of novel anti-influenza inhibitors with the ability to inhibit resistant strains.
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Affiliation(s)
- Sphamadla E. Mtambo
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Daniel G. Amoako
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
- Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg 2131, South Africa
| | - Anou M. Somboro
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
- Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg 2131, South Africa
| | - Clement Agoni
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Monsurat M. Lawal
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Nelisiwe S. Gumede
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Rene B. Khan
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
| | - Hezekiel M. Kumalo
- Drug Research and Innovation Unit, Discipline of Medical Biochemistry, School of Laboratory Medicine and Medical Science, University of KwaZulu-Natal, Durban 4000, South Africa; (S.E.M.); (A.M.S.); (C.A.); (M.M.L.); (N.S.G.); (R.B.K.)
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21
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Gut bacteria are essential for normal cuticle development in herbivorous turtle ants. Nat Commun 2021; 12:676. [PMID: 33514729 PMCID: PMC7846594 DOI: 10.1038/s41467-021-21065-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 01/12/2021] [Indexed: 11/08/2022] Open
Abstract
Across the evolutionary history of insects, the shift from nitrogen-rich carnivore/omnivore diets to nitrogen-poor herbivorous diets was made possible through symbiosis with microbes. The herbivorous turtle ants Cephalotes possess a conserved gut microbiome which enriches the nutrient composition by recycling nitrogen-rich metabolic waste to increase the production of amino acids. This enrichment is assumed to benefit the host, but we do not know to what extent. To gain insights into nitrogen assimilation in the ant cuticle we use gut bacterial manipulation, 15N isotopic enrichment, isotope-ratio mass spectrometry, and 15N nuclear magnetic resonance spectroscopy to demonstrate that gut bacteria contribute to the formation of proteins, catecholamine cross-linkers, and chitin in the cuticle. This study identifies the cuticular components which are nitrogen-enriched by gut bacteria, highlighting the role of symbionts in insect evolution, and provides a framework for understanding the nitrogen flow from nutrients through bacteria into the insect cuticle.
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22
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Li F, Egea PF, Vecchio AJ, Asial I, Gupta M, Paulino J, Bajaj R, Dickinson MS, Ferguson-Miller S, Monk BC, Stroud RM. Highlighting membrane protein structure and function: A celebration of the Protein Data Bank. J Biol Chem 2021; 296:100557. [PMID: 33744283 PMCID: PMC8102919 DOI: 10.1016/j.jbc.2021.100557] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 02/10/2021] [Accepted: 03/16/2021] [Indexed: 12/13/2022] Open
Abstract
Biological membranes define the boundaries of cells and compartmentalize the chemical and physical processes required for life. Many biological processes are carried out by proteins embedded in or associated with such membranes. Determination of membrane protein (MP) structures at atomic or near-atomic resolution plays a vital role in elucidating their structural and functional impact in biology. This endeavor has determined 1198 unique MP structures as of early 2021. The value of these structures is expanded greatly by deposition of their three-dimensional (3D) coordinates into the Protein Data Bank (PDB) after the first atomic MP structure was elucidated in 1985. Since then, free access to MP structures facilitates broader and deeper understanding of MPs, which provides crucial new insights into their biological functions. Here we highlight the structural and functional biology of representative MPs and landmarks in the evolution of new technologies, with insights into key developments influenced by the PDB in magnifying their impact.
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Affiliation(s)
- Fei Li
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA; Department of Neurology, University of California San Francisco, San Francisco, California, USA
| | - Pascal F Egea
- Department of Biological Chemistry, School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Alex J Vecchio
- Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | | | - Meghna Gupta
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Joana Paulino
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Ruchika Bajaj
- Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, California, USA
| | - Miles Sasha Dickinson
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA
| | - Brian C Monk
- Sir John Walsh Research Institute and Department of Oral Sciences, University of Otago, North Dunedin, Dunedin, New Zealand
| | - Robert M Stroud
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA.
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23
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Watkins LC, DeGrado WF, Voth GA. Influenza A M2 Inhibitor Binding Understood through Mechanisms of Excess Proton Stabilization and Channel Dynamics. J Am Chem Soc 2020; 142:17425-17433. [PMID: 32933245 PMCID: PMC7564090 DOI: 10.1021/jacs.0c06419] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
![]()
Prevalent resistance to inhibitors
that target the influenza A
M2 proton channel has necessitated a continued drug design effort,
supported by a sustained study of the mechanism of channel function
and inhibition. Recent high-resolution X-ray crystal structures present
the first opportunity to see how the adamantyl amine class of inhibitors
bind to M2 and disrupt and interact with the channel’s water
network, providing insight into the critical properties that enable
their effective inhibition in wild-type M2. In this work, we examine
the hypothesis that these drugs act primarily as mechanism-based inhibitors
by comparing hydrated excess proton stabilization during proton transport
in M2 with the interactions revealed in the crystal structures, using
the Multiscale Reactive Molecular Dynamics (MS-RMD) methodology. MS-RMD,
unlike classical molecular dynamics, models the hydrated proton (hydronium-like
cation) as a dynamic excess charge defect and allows bonds to break
and form, capturing the intricate interactions between the hydrated
excess proton, protein atoms, and water. Through this, we show that
the ammonium group of the inhibitors is effectively positioned to
take advantage of the channel’s natural ability to stabilize
an excess protonic charge and act as a hydronium mimic. Additionally,
we show that the channel is especially stable in the drug binding
region, highlighting the importance of this property for binding the
adamantane group. Finally, we characterize an additional hinge point
near Val27, which dynamically responds to charge and inhibitor binding.
Altogether, this work further illuminates a dynamic understanding
of the mechanism of drug inhibition in M2, grounded in the fundamental
properties that enable the channel to transport and stabilize excess
protons, with critical implications for future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94158, United States
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, Institute for Biophysical Dynamics and James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
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24
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McGuire KL, Hill JT, Busath DD. Increased Dissociation of Adamantanamines in Influenza A M2 S31N with Partial Block by Rimantadine. Biophys J 2020; 119:1811-1820. [PMID: 33080223 DOI: 10.1016/j.bpj.2020.09.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 08/06/2020] [Accepted: 09/15/2020] [Indexed: 11/15/2022] Open
Abstract
The ubiquitous mutation from serine (WT) to asparagine at residue 31 (S31N) in the influenza A M2 channel renders it insensitive to amantadine (AMT) and rimantadine (RMT) block, but it is unknown whether the inhibition results from weak binding or incomplete block. Two-electrode voltage clamp (TEVC) of transfected Xenopus oocytes revealed that the M2 S31N channel is essentially fully blocked by AMT at 10 mM, demonstrating that, albeit weak, AMT binding in a channel results in complete block of its proton current. In contrast, RMT achieves only a modest degree of block in the M2 S31N channel at 1 mM, with very little increase in block at 10 mM, indicating that the RMT binding site in the channel saturates with only modest block. From exponential curve fits to families of proton current wash-in and wash-out traces, the association rate constant (k1) is somewhat decreased for both AMT and RMT in the S31N, but the dissociation rate constant (k2) is dramatically increased compared with WT. The potentials of mean force (PMF) from adaptive biasing force (ABF) molecular dynamics simulations predict that rate constants should be exquisitely sensitive to the charge state of the His37 selectivity filter of M2. With one exception out of eight cases, predictions from the simulations with one and three charged side chains bracket the experimental rate constants, as expected for the acidic bath used in the TEVC assay. From simulations, the weak binding can be accounted for by changes in the potentials of mean force, but the partial block by RMT remains unexplained.
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Affiliation(s)
- Kelly L McGuire
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah.
| | - Jonathon T Hill
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah
| | - David D Busath
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah
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25
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Tan C, Chen Y, Peng X, Chen Z, Cai S, Cross TA, Fu R. Revealing weak histidine 15N homonuclear scalar couplings using Solid-State Magic-Angle-Spinning NMR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 316:106757. [PMID: 32535401 PMCID: PMC7426724 DOI: 10.1016/j.jmr.2020.106757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2020] [Revised: 05/12/2020] [Accepted: 05/27/2020] [Indexed: 05/05/2023]
Abstract
The tautomeric structure and chemistry of the histidine imidazole ring play active roles in many structurally and functionally important proteins and polypeptides. While in NMR spectroscopy histidine chemical shifts (e.g. 15N, 13C, and 1H) have been commonly used to characterize the tautomeric structure, hydrogen bonding, and torsion angles, homonuclear 15N scalar couplings in histidine have rarely been reported. Here, we propose double spin-echo sequences to compare the observed signals with and without a 90° pulse between the two spin-echo periods, such that their signal ratio as a function of the echo time solely depends on homonuclear scalar couplings, allowing for measuring weak homonuclear scalar couplings without influence from transverse dephasing effects, thus capable of revealing hydrogen-bond mediated 15N-15N J-couplings that can provide direct and definitive evidence for the formation of N…H…N hydrogen-bonding associated with the imidazole ring. We used two 13C,15N labeled histidine samples recrystallized from solutions at pH 6.3 and pH 11.0 to demonstrate the feasibility of this method and reveal the existence of a weak two-bond scalar coupling between the Nδ1 and Nε2 sites in the histidine imidazole ring in three tautomeric states and the presence of a hydrogen-bond mediated scalar coupling between the Nδ1 site in the imidazole ring and the backbone Nα site in the histidine neutral τ and π states. Our results demonstrate that weak 15N homonuclear scalar couplings can be measured even when their values are less than their corresponding intrinsic natural linewidths, thus providing direct and definitive evidence for the formation of N…H…N hydrogen bonding that is associated with the histidine imidazole ring.
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Affiliation(s)
- Chunhua Tan
- National High Magnet Field Lab, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA; Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian 361005, China
| | - Yuquan Chen
- CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xinhua Peng
- CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
| | - Zhong Chen
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian 361005, China
| | - Shuhui Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian 361005, China
| | - Timothy A Cross
- National High Magnet Field Lab, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
| | - Riqiang Fu
- National High Magnet Field Lab, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
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26
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Li J, Sae Her A, Traaseth NJ. Site-specific resolution of anionic residues in proteins using solid-state NMR spectroscopy. JOURNAL OF BIOMOLECULAR NMR 2020; 74:355-363. [PMID: 32514875 PMCID: PMC7472563 DOI: 10.1007/s10858-020-00323-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 05/29/2020] [Indexed: 06/11/2023]
Abstract
NMR spectroscopy is commonly used to infer site-specific acid dissociation constants (pKa) since the chemical shift is sensitive to the protonation state. Methods that probe atoms nearest to the functional groups involved in acid/base chemistry are the most sensitive for determining the protonation state. In this work, we describe a magic-angle-spinning (MAS) solid-state NMR approach to measure chemical shifts on the side chain of the anionic residues aspartate and glutamate. This method involves a combination of double quantum spectroscopy in the indirect dimension and REDOR dephasing to provide a sensitive and resolved view of these amino acid residues that are commonly involved in enzyme catalysis and membrane protein transport. To demonstrate the applicability of the approach, we carried out measurements using a microcrystalline soluble protein (ubiquitin) and a membrane protein embedded in lipid bilayers (EmrE). Overall, the resolution available from the double quantum dimension and confidence in identification of aspartate and glutamate residues from the REDOR filter make this method the most convenient for characterizing protonation states and deriving pKa values using MAS solid-state NMR.
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Affiliation(s)
- Jianping Li
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY, 10003, USA
| | - Ampon Sae Her
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY, 10003, USA
| | - Nathaniel J Traaseth
- Department of Chemistry, New York University, 100 Washington Square East, New York, NY, 10003, USA.
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27
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Movellan K, Wegstroth M, Overkamp K, Leonov A, Becker S, Andreas LB. Imidazole-Imidazole Hydrogen Bonding in the pH-Sensing Histidine Side Chains of Influenza A M2. J Am Chem Soc 2020; 142:2704-2708. [PMID: 31970979 PMCID: PMC7307898 DOI: 10.1021/jacs.9b10984] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Indexed: 12/28/2022]
Abstract
The arrangement of histidine side chains in influenza A M2 tetramer determines their pKa values, which define pH-controlled proton conduction critical to the virus lifecycle. Both water-associated and hydrogen-bonded imidazole-imidazolium histidine quaternary structures have been proposed, based on crystal structures and NMR chemical shifts, respectively. Here we show, using the conduction domain construct of M2 in lipid bilayers, that the imidazole rings are hydrogen bonded even at a pH of 7.8 in the neutral charge state. An intermolecular 8.9 ± 0.3 Hz 2hJNN hydrogen bond is observed between H37 Nε and Nδ recorded in a fully protonated sample with 100 kHz magic-angle spinning. This interaction could not be detected in the drug-bound sample.
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Affiliation(s)
- Kumar
Tekwani Movellan
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Melanie Wegstroth
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Kerstin Overkamp
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Andrei Leonov
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Stefan Becker
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Loren B. Andreas
- Department of NMR Based Structural
Biology, Max Planck Institute for Biophysical
Chemistry, Am Fassberg 11, Göttingen 37077, Germany
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28
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M2 amphipathic helices facilitate pH-dependent conformational transition in influenza A virus. Proc Natl Acad Sci U S A 2020; 117:3583-3591. [PMID: 32015120 DOI: 10.1073/pnas.1913385117] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The matrix-2 (M2) protein from influenza A virus is a tetrameric, integral transmembrane (TM) protein that plays a vital role in viral replication by proton flux into the virus. The His37 tetrad is a pH sensor in the center of the M2 TM helix that activates the channel in response to the low endosomal pH. M2 consists of different regions that are believed to be involved in membrane targeting, packaging, nucleocapsid binding, and proton transport. Although M2 has been the target of many experimental and theoretical studies that have led to significant insights into its structure and function under differing conditions, the main mechanism of proton transport, its conformational dynamics, and the role of the amphipathic helices (AHs) on proton conductance remain elusive. To this end, we have applied explicit solvent constant pH molecular dynamics using the multisite λ-dynamics approach (CpHMDMSλD) to investigate the buried ionizable residues comprehensively and to elucidate their effect on the conformational transition. Our model recapitulates the pH-dependent conformational transition of M2 from closed to open state when the AH domain is included in the M2 construct, revealing the role of the amphipathic helices on this transition and shedding light on the proton-transport mechanism. This work demonstrates the importance of including the amphipathic helices in future experimental and theoretical studies of ion channels. Finally, our work shows that explicit solvent CpHMDMSλD provides a realistic pH-dependent model for membrane proteins.
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29
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Fu R, Miao Y, Qin H, Cross TA. Observation of the Imidazole-Imidazolium Hydrogen Bonds Responsible for Selective Proton Conductance in the Influenza A M2 Channel. J Am Chem Soc 2020; 142:2115-2119. [PMID: 31970982 DOI: 10.1021/jacs.9b09985] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The integral membrane M2 protein is a 97-residue membrane protein that assembles as a tetramer to conduct protons at a slow rate (102-103/s) when activated by low pH. The proton conductance mechanism has been extensively debated in the literature, but it is accepted that the proton conductance is facilitated by hydrogen bonds involving the His37 residues. However, the hydrogen bonding partnership remains unresolved. Here, we report on the measurement of 15N-15N J-couplings of 15N His37-labeled full length M2 (M2FL) protein from Influenza A virus embedded in synthetic liquid crystalline lipid bilayers using two-dimensional J-resolved NMR spectroscopy. We experimentally observed the hydrogen-bond mediated J-couplings between Nδ1 and Nε2 of adjacent His37 imidazole rings, providing direct evidence for the existence of various imidazolium-imidazole hydrogen-bonding geometries in the histidine tetrad at low pH, thus validating the proton conduction mechanism in the M2FL protein by which the proton is transferred through the breaking and reforming of the hydrogen bonds between pairs of His37 residues.
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Affiliation(s)
- Riqiang Fu
- National High Magnet Field Lab , 1800 East Paul Dirac Drive , Tallahassee , Florida 32310 , United States
| | - Yimin Miao
- Department of Chemistry and Biochemistry , Florida State University , Tallahassee , Florida 32306 , United States
| | - Huajun Qin
- Department of Chemistry and Biochemistry , Florida State University , Tallahassee , Florida 32306 , United States
| | - Timothy A Cross
- National High Magnet Field Lab , 1800 East Paul Dirac Drive , Tallahassee , Florida 32310 , United States.,Department of Chemistry and Biochemistry , Florida State University , Tallahassee , Florida 32306 , United States
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30
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Kariev AM, Green ME. Quantum Calculation of Proton and Other Charge Transfer Steps in Voltage Sensing in the Kv1.2 Channel. J Phys Chem B 2019; 123:7984-7998. [DOI: 10.1021/acs.jpcb.9b05448] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alisher M. Kariev
- Department of Chemistry and Biochemistry, City College of New York, New York, New York 10011, United States
| | - Michael E. Green
- Department of Chemistry and Biochemistry, City College of New York, New York, New York 10011, United States
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31
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Watkins LC, Liang R, Swanson JMJ, DeGrado WF, Voth GA. Proton-Induced Conformational and Hydration Dynamics in the Influenza A M2 Channel. J Am Chem Soc 2019; 141:11667-11676. [PMID: 31264413 DOI: 10.1021/jacs.9b05136] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The influenza A M2 protein is an acid-activated proton channel responsible for acidification of the inside of the virus, a critical step in the viral life cycle. This channel has four central histidine residues that form an acid-activated gate, binding protons from the outside until an activated state allows proton transport to the inside. While previous work has focused on proton transport through the channel, the structural and dynamic changes that accompany proton flux and enable activation have yet to be resolved. In this study, extensive Multiscale Reactive Molecular Dynamics simulations with explicit Grotthuss-shuttling hydrated excess protons are used to explore detailed molecular-level interactions that accompany proton transport in the +0, + 1, and +2 histidine charge states. The results demonstrate how the hydrated excess proton strongly influences both the protein and water hydrogen-bonding network throughout the channel, providing further insight into the channel's acid-activation mechanism and rectification behavior. We find that the excess proton dynamically, as a function of location, shifts the protein structure away from its equilibrium distributions uniquely for different pH conditions consistent with acid-activation. The proton distribution in the xy-plane is also shown to be asymmetric about the channel's main axis, which has potentially important implications for the mechanism of proton conduction and future drug design efforts.
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Affiliation(s)
- Laura C Watkins
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Ruibin Liang
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Gregory A Voth
- Department of Chemistry, Institute for Biophysical Dynamics and James Franck Institute , The University of Chicago , Chicago , Illinois 60637 , United States
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32
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Thomaston JL, Wu Y, Polizzi N, Liu L, Wang J, DeGrado WF. X-ray Crystal Structure of the Influenza A M2 Proton Channel S31N Mutant in Two Conformational States: An Open and Shut Case. J Am Chem Soc 2019; 141:11481-11488. [PMID: 31184871 DOI: 10.1021/jacs.9b02196] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The amantadine-resistant S31N mutant of the influenza A M2 proton channel has become prevalent in currently circulating viruses. Here, we have solved an X-ray crystal structure of M2(22-46) S31N that contains two distinct conformational states within its asymmetric unit. This structure reveals the mechanism of adamantane resistance in both conformational states of the M2 channel. In the Inwardopen conformation, the mutant Asn31 side chain faces the channel pore and sterically blocks the adamantane binding site. In the Inwardclosed conformation, Asn31 forms hydrogen bonds with carbonyls at the monomer-monomer interface, which twists the monomer helices and constricts the channel pore at the drug binding site. We also examine M2(19-49) WT and S31N using solution NMR spectroscopy and show that distribution of the two conformational states is dependent on both detergent choice and experimental pH.
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Affiliation(s)
- Jessica L Thomaston
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Yibing Wu
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Nicholas Polizzi
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Lijun Liu
- State Key Laboratory of Chemical Oncogenomics , Peking University Shenzhen Graduate School , Shenzhen 518055 , China.,DLX Scientific , Lawrence , Kansas 66049 , United States
| | - Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy , University of Arizona , Tucson , Arizona 85721 , United States
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
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33
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To J, Torres J. Viroporins in the Influenza Virus. Cells 2019; 8:cells8070654. [PMID: 31261944 PMCID: PMC6679168 DOI: 10.3390/cells8070654] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2019] [Revised: 06/21/2019] [Accepted: 06/27/2019] [Indexed: 12/28/2022] Open
Abstract
Influenza is a highly contagious virus that causes seasonal epidemics and unpredictable pandemics. Four influenza virus types have been identified to date: A, B, C and D, with only A–C known to infect humans. Influenza A and B viruses are responsible for seasonal influenza epidemics in humans and are responsible for up to a billion flu infections annually. The M2 protein is present in all influenza types and belongs to the class of viroporins, i.e., small proteins that form ion channels that increase membrane permeability in virus-infected cells. In influenza A and B, AM2 and BM2 are predominantly proton channels, although they also show some permeability to monovalent cations. By contrast, M2 proteins in influenza C and D, CM2 and DM2, appear to be especially selective for chloride ions, with possibly some permeability to protons. These differences point to different biological roles for M2 in types A and B versus C and D, which is also reflected in their sequences. AM2 is by far the best characterized viroporin, where mechanistic details and rationale of its acid activation, proton selectivity, unidirectionality, and relative low conductance are beginning to be understood. The present review summarizes the biochemical and structural aspects of influenza viroporins and discusses the most relevant aspects of function, inhibition, and interaction with the host.
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Affiliation(s)
- Janet To
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
| | - Jaume Torres
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore.
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34
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Kwon B, Roos M, Mandala VS, Shcherbakov AA, Hong M. Elucidating Relayed Proton Transfer through a His-Trp-His Triad of a Transmembrane Proton Channel by Solid-State NMR. J Mol Biol 2019; 431:2554-2566. [PMID: 31082440 DOI: 10.1016/j.jmb.2019.05.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 04/13/2019] [Accepted: 05/05/2019] [Indexed: 01/02/2023]
Abstract
Proton transfer through membrane-bound ion channels is mediated by both water and polar residues of proteins, but the detailed molecular mechanism is challenging to determine. The tetrameric influenza A and B virus M2 proteins form canonical proton channels that use an HxxxW motif for proton selectivity and gating. The BM2 channel also contains a second histidine (His), H27, equidistant from the gating tryptophan, which leads to a symmetric H19xxxW23xxxH27 motif. The proton-dissociation constants (pKa's) of H19 in BM2 were found to be much lower than the pKa's of H37 in AM2. To determine if the lower pKa's result from H27-facilitated proton dissociation of H19, we have now investigated a H27A mutant of BM2 using solid-state NMR. 15N NMR spectra indicate that removal of the second histidine converted the protonation and tautomeric equilibria of H19 to be similar to the H37 behavior in AM2, indicating that the peripheral H27 is indeed the origin of the low pKa's of H19 in wild-type BM2. Measured interhelical distances between W23 sidechains indicate that the pore constriction at W23 increases with the H19 tetrad charge but is independent of the H27A mutation. These results indicate that H27 both accelerates proton dissociation from H19 to increase the inward proton conductance and causes the small reverse conductance of BM2. The proton relay between H19 and H27 is likely mediated by the intervening gating tryptophan through cation-π interactions. This relayed proton transfer may exist in other ion channels and has implications for the design of imidazole-based synthetic proton channels.
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Affiliation(s)
- Byungsu Kwon
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA
| | - Matthias Roos
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA
| | - Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA
| | - Alexander A Shcherbakov
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, USA.
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35
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Fudim R, Szczepek M, Vierock J, Vogt A, Schmidt A, Kleinau G, Fischer P, Bartl F, Scheerer P, Hegemann P. Design of a light-gated proton channel based on the crystal structure of Coccomyxa rhodopsin. Sci Signal 2019; 12:12/573/eaav4203. [PMID: 30890657 DOI: 10.1126/scisignal.aav4203] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The light-driven proton pump Coccomyxa subellipsoidea rhodopsin (CsR) provides-because of its high expression in heterologous host cells-an opportunity to study active proton transport under controlled electrochemical conditions. In this study, solving crystal structure of CsR at 2.0-Å resolution enabled us to identify distinct features of the membrane protein that determine ion transport directivity and voltage sensitivity. A specific hydrogen bond between the highly conserved Arg83 and the nearby nonconserved tyrosine (Tyr14) guided our structure-based transformation of CsR into an operational light-gated proton channel (CySeR) that could potentially be used in optogenetic assays. Time-resolved electrophysiological and spectroscopic measurements distinguished pump currents from channel currents in a single protein and emphasized the necessity of Arg83 mobility in CsR as a dynamic extracellular barrier to prevent passive conductance. Our findings reveal that molecular constraints that distinguish pump from channel currents are structurally more confined than was generally expected. This knowledge might enable the structure-based design of novel optogenetic tools, which derive from microbial pumps and are therefore ion specific.
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Affiliation(s)
- Roman Fudim
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany
| | - Michal Szczepek
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Institute for Medical Physics and Biophysics, Group Protein X-ray Crystallography & Signal Transduction, Charitéplatz 1, D-10117 Berlin, Germany
| | - Johannes Vierock
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany
| | - Arend Vogt
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany
| | - Andrea Schmidt
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Institute for Medical Physics and Biophysics, Group Protein X-ray Crystallography & Signal Transduction, Charitéplatz 1, D-10117 Berlin, Germany
| | - Gunnar Kleinau
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Institute for Medical Physics and Biophysics, Group Protein X-ray Crystallography & Signal Transduction, Charitéplatz 1, D-10117 Berlin, Germany
| | - Paul Fischer
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany
| | - Franz Bartl
- Biophysical Chemistry, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany
| | - Patrick Scheerer
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Institute for Medical Physics and Biophysics, Group Protein X-ray Crystallography & Signal Transduction, Charitéplatz 1, D-10117 Berlin, Germany.
| | - Peter Hegemann
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115 Berlin, Germany.
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36
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Christou NE, Brutscher B. BEST and SOFAST experiments for resonance assignment of histidine and tyrosine side chains in 13C/ 15N labeled proteins. JOURNAL OF BIOMOLECULAR NMR 2018; 72:115-124. [PMID: 30465113 DOI: 10.1007/s10858-018-0216-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 11/16/2018] [Indexed: 06/09/2023]
Abstract
Aromatic amino-acid side chains are essential components for the structure and function of proteins. We present herein a set of NMR experiments for time-efficient resonance assignment of histidine and tyrosine side chains in uniformly 13C/15N-labeled proteins. The use of band-selective 13C pulses allows to deal with linear chains of coupled spins, thus avoiding signal loss that occurs in branched spin systems during coherence transfer. Furthermore, our pulse schemes make use of longitudinal 1H relaxation enhancement, Ernst-angle excitation, and simultaneous detection of 1H and 13C steady-state polarization to achieve significant signal enhancements.
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37
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The Role of Proton Transport in Gating Current in a Voltage Gated Ion Channel, as Shown by Quantum Calculations. SENSORS 2018; 18:s18093143. [PMID: 30231473 PMCID: PMC6163810 DOI: 10.3390/s18093143] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 09/05/2018] [Accepted: 09/12/2018] [Indexed: 11/25/2022]
Abstract
Over two-thirds of a century ago, Hodgkin and Huxley proposed the existence of voltage gated ion channels (VGICs) to carry Na+ and K+ ions across the cell membrane to create the nerve impulse, in response to depolarization of the membrane. The channels have multiple physiological roles, and play a central role in a wide variety of diseases when they malfunction. The first channel structure was found by MacKinnon and coworkers in 1998. Subsequently, the structure of a number of VGICs was determined in the open (ion conducting) state. This type of channel consists of four voltage sensing domains (VSDs), each formed from four transmembrane (TM) segments, plus a pore domain through which ions move. Understanding the gating mechanism (how the channel opens and closes) requires structures. One TM segment (S4) has an arginine in every third position, with one such segment per domain. It is usually assumed that these arginines are all ionized, and in the resting state are held toward the intracellular side of the membrane by voltage across the membrane. They are assumed to move outward (extracellular direction) when released by depolarization of this voltage, producing a capacitive gating current and opening the channel. We suggest alternate interpretations of the evidence that led to these models. Measured gating current is the total charge displacement of all atoms in the VSD; we propose that the prime, but not sole, contributor is proton motion, not displacement of the charges on the arginines of S4. It is known that the VSD can conduct protons. Quantum calculations on the Kv1.2 potassium channel VSD show how; the key is the amphoteric nature of the arginine side chain, which allows it to transfer a proton. This appears to be the first time the arginine side chain has had its amphoteric character considered. We have calculated one such proton transfer in detail: this proton starts from a tyrosine that can ionize, transferring to the NE of the third arginine on S4; that arginine’s NH then transfers a proton to a glutamate. The backbone remains static. A mutation predicted to affect the proton transfer has been qualitatively confirmed experimentally, from the change in the gating current-voltage curve. The total charge displacement in going from a normal closed potential of −70 mV across the membrane to 0 mV (open), is calculated to be approximately consistent with measured values, although the error limits on the calculation require caution in interpretation.
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38
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Thomaston JL, Polizzi NF, Konstantinidi A, Wang J, Kolocouris A, DeGrado WF. Inhibitors of the M2 Proton Channel Engage and Disrupt Transmembrane Networks of Hydrogen-Bonded Waters. J Am Chem Soc 2018; 140:15219-15226. [PMID: 30165017 DOI: 10.1021/jacs.8b06741] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Water-mediated interactions play key roles in drug binding. In protein sites with sparse polar functionality, a small-molecule approach is often viewed as insufficient to achieve high affinity and specificity. Here we show that small molecules can enable potent inhibition by targeting key waters. The M2 proton channel of influenza A is the target of the antiviral drugs amantadine and rimantadine. Structural studies of drug binding to the channel using X-ray crystallography have been limited because of the challenging nature of the target, with the one previously solved crystal structure limited to 3.5 Å resolution. Here we describe crystal structures of amantadine bound to M2 in the Inwardclosed conformation (2.00 Å), rimantadine bound to M2 in both the Inwardclosed (2.00 Å) and Inwardopen (2.25 Å) conformations, and a spiro-adamantyl amine inhibitor bound to M2 in the Inwardclosed conformation (2.63 Å). These X-ray crystal structures of the M2 proton channel with bound inhibitors reveal that ammonium groups bind to water-lined sites that are hypothesized to stabilize transient hydronium ions formed in the proton-conduction mechanism. Furthermore, the ammonium and adamantyl groups of the adamantyl-amine class of drugs are free to rotate in the channel, minimizing the entropic cost of binding. These drug-bound complexes provide the first high-resolution structures of drugs that interact with and disrupt networks of hydrogen-bonded waters that are widely utilized throughout nature to facilitate proton diffusion within proteins.
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Affiliation(s)
- Jessica L Thomaston
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Nicholas F Polizzi
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
| | - Athina Konstantinidi
- Department of Pharmaceutical Chemistry , National and Kapodistrian University of Athens , 15771 Athens , Greece
| | - Jun Wang
- Department of Pharmacology and Toxicology, College of Pharmacy , University of Arizona , Tucson , Arizona 85721 , United States
| | - Antonios Kolocouris
- Department of Pharmaceutical Chemistry , National and Kapodistrian University of Athens , 15771 Athens , Greece
| | - William F DeGrado
- Department of Pharmaceutical Chemistry , University of California , San Francisco , California 94158 , United States
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Cao Y, Dong Y, Chou JJ. Structural and Functional Properties of Viral Membrane Proteins. ADVANCES IN MEMBRANE PROTEINS 2018. [PMCID: PMC7122571 DOI: 10.1007/978-981-13-0532-0_6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Viruses have developed a large variety of transmembrane proteins to carry out their infectious cycles. Some of these proteins are simply anchored to membrane via transmembrane helices. Others, however, adopt more interesting structures to perform tasks such as mediating membrane fusion and forming ion-permeating channels. Due to the dynamic or plastic nature shown by many of the viral membrane proteins, structural and mechanistic understanding of these proteins has lagged behind their counterparts in prokaryotes and eukaryotes. This chapter provides an overview of the use of NMR spectroscopy to unveil the transmembrane and membrane-proximal regions of viral membrane proteins, as well as their interactions with potential therapeutics.
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Affiliation(s)
- Yu Cao
- Institute of Precision Medicine, The Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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40
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Matlahov I, van der Wel PCA. Hidden motions and motion-induced invisibility: Dynamics-based spectral editing in solid-state NMR. Methods 2018; 148:123-135. [PMID: 29702226 DOI: 10.1016/j.ymeth.2018.04.015] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 04/05/2018] [Accepted: 04/16/2018] [Indexed: 10/17/2022] Open
Abstract
Solid-state nuclear magnetic resonance (ssNMR) spectroscopy enables the structural characterization of a diverse array of biological assemblies that include amyloid fibrils, non-amyloid aggregates, membrane-associated proteins and viral capsids. Such biological samples feature functionally relevant molecular dynamics, which often affect different parts of the sample in different ways. Solid-state NMR experiments' sensitivity to dynamics represents a double-edged sword. On the one hand, it offers a chance to measure dynamics in great detail. On the other hand, certain types of motion lead to signal loss and experimental inefficiencies that at first glance interfere with the application of ssNMR to overly dynamic proteins. Dynamics-based spectral editing (DYSE) ssNMR methods leverage motion-dependent signal losses to simplify spectra and enable the study of sub-structures with particular motional properties.
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Affiliation(s)
- Irina Matlahov
- Department of Structural Biology, University of Pittsburgh School of Medicine, 3501 Fifth Ave., Pittsburgh, PA 15213, USA
| | - Patrick C A van der Wel
- Department of Structural Biology, University of Pittsburgh School of Medicine, 3501 Fifth Ave., Pittsburgh, PA 15213, USA; Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
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41
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Abstract
Solid-state nuclear magnetic resonance (SSNMR) spectroscopy elucidates membrane protein structures and dynamics in atomic detail to yield mechanistic insights. By interrogating membrane proteins in phospholipid bilayers that closely resemble biological membranes, SSNMR spectroscopists have revealed ion conduction mechanisms, substrate transport dynamics, and oligomeric interfaces of seven-transmembrane helix proteins. Research has also identified conformational plasticity underlying virus-cell membrane fusions by complex protein machineries, and β-sheet folding and assembly by amyloidogenic proteins bound to lipid membranes. These studies collectively show that membrane proteins exhibit extensive structural plasticity to carry out their functions. Because of the inherent dependence of NMR frequencies on molecular orientations and the sensitivity of NMR frequencies to dynamical processes on timescales from nanoseconds to seconds, SSNMR spectroscopy is ideally suited to elucidate such structural plasticity, local and global conformational dynamics, protein-lipid and protein-ligand interactions, and protonation states of polar residues. New sensitivity-enhancement techniques, resolution enhancement by ultrahigh magnetic fields, and the advent of 3D and 4D correlation NMR techniques are increasingly aiding these mechanistically important structural studies.
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Affiliation(s)
- Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
| | - Jonathan K Williams
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
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42
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McKay MJ, Afrose F, Koeppe RE, Greathouse DV. Helix formation and stability in membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2108-2117. [PMID: 29447916 DOI: 10.1016/j.bbamem.2018.02.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 02/06/2018] [Accepted: 02/07/2018] [Indexed: 01/05/2023]
Abstract
In this article we review current understanding of basic principles for the folding of membrane proteins, focusing on the more abundant alpha-helical class. Membrane proteins, vital to many biological functions and implicated in numerous diseases, fold into their active conformations in the complex environment of the cell bilayer membrane. While many membrane proteins rely on the translocon and chaperone proteins to fold correctly, others can achieve their functional form in the absence of any translation apparatus or other aides. Nevertheless, the spontaneous folding process is not well understood at the molecular level. Recent findings suggest that helix fraying and loop formation may be important for overall structure, dynamics and regulation of function. Several types of membrane helices with ionizable amino acids change their topology with pH. Additionally we note that some peptides, including many that are rich in arginine, and a particular analogue of gramicidin, are able passively to translocate across cell membranes. The findings indicate that a final protein structure in a lipid-bilayer membrane is sequence-based, with lipids contributing to stability and regulation. While much progress has been made toward understanding the folding process for alpha-helical membrane proteins, it remains a work in progress. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.
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Affiliation(s)
- Matthew J McKay
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Fahmida Afrose
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
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43
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Mandala VS, Gelenter MD, Hong M. Transport-Relevant Protein Conformational Dynamics and Water Dynamics on Multiple Time Scales in an Archetypal Proton Channel: Insights from Solid-State NMR. J Am Chem Soc 2018; 140:1514-1524. [PMID: 29303574 DOI: 10.1021/jacs.7b12464] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The influenza M2 protein forms a tetrameric proton channel that conducts protons from the acidic endosome into the virion by shuttling protons between water and a transmembrane histidine. Previous NMR studies have shown that this histidine protonates and deprotonates on the microsecond time scale. However, M2's proton conduction rate is 10-1000 s-1, more than 2 orders of magnitude slower than the histidine-water proton-exchange rate. M2 is also known to be conformationally plastic. To address the disparity between the functional time scale and the time scales of protein conformational dynamics and water dynamics, we have now investigated a W41F mutant of the M2 transmembrane domain using solid-state NMR. 13C chemical shifts of the membrane-bound peptide indicate the presence of two distinct tetramer conformations, whose concentrations depend exclusively on pH and hence the charge-state distribution of the tetramers. High-temperature 2D correlation spectra indicate that these two conformations interconvert at a rate of ∼400 s-1 when the +2 and +3 charge states dominate, which gives the first experimental evidence of protein conformational motion on the transport time scale. Protein 13C-detected water 1H T2 relaxation measurements show that channel water relaxes an order of magnitude faster than bulk water and membrane-associated water, indicating that channel water undergoes nanosecond motion in a pH-independent fashion. These results connect motions on three time scales to explain M2's proton-conduction mechanism: picosecond-to-nanosecond motions of water molecules facilitate proton Grotthuss hopping, microsecond motions of the histidine side chain allow water-histidine proton transfer, while millisecond motions of the entire four-helix bundle constitute the rate-limiting step, dictating the number of protons released into the virion.
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Affiliation(s)
- Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology , 170 Albany Street, Cambridge, Massachusetts 02139, United States
| | - Martin D Gelenter
- Department of Chemistry, Massachusetts Institute of Technology , 170 Albany Street, Cambridge, Massachusetts 02139, United States
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology , 170 Albany Street, Cambridge, Massachusetts 02139, United States
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44
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Zhou HX, Pang X. Electrostatic Interactions in Protein Structure, Folding, Binding, and Condensation. Chem Rev 2018; 118:1691-1741. [PMID: 29319301 DOI: 10.1021/acs.chemrev.7b00305] [Citation(s) in RCA: 454] [Impact Index Per Article: 75.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Charged and polar groups, through forming ion pairs, hydrogen bonds, and other less specific electrostatic interactions, impart important properties to proteins. Modulation of the charges on the amino acids, e.g., by pH and by phosphorylation and dephosphorylation, have significant effects such as protein denaturation and switch-like response of signal transduction networks. This review aims to present a unifying theme among the various effects of protein charges and polar groups. Simple models will be used to illustrate basic ideas about electrostatic interactions in proteins, and these ideas in turn will be used to elucidate the roles of electrostatic interactions in protein structure, folding, binding, condensation, and related biological functions. In particular, we will examine how charged side chains are spatially distributed in various types of proteins and how electrostatic interactions affect thermodynamic and kinetic properties of proteins. Our hope is to capture both important historical developments and recent experimental and theoretical advances in quantifying electrostatic contributions of proteins.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Chemistry and Department of Physics, University of Illinois at Chicago , Chicago, Illinois 60607, United States.,Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
| | - Xiaodong Pang
- Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
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45
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Zhu Q, Lu Y, He X, Liu T, Chen H, Wang F, Zheng D, Dong H, Ma J. Entropy and Polarity Control the Partition and Transportation of Drug-like Molecules in Biological Membrane. Sci Rep 2017; 7:17749. [PMID: 29255188 PMCID: PMC5735159 DOI: 10.1038/s41598-017-18012-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 12/05/2017] [Indexed: 11/09/2022] Open
Abstract
Partition and transportation of drug in the plasma membrane of a mammalian cell are the prerequisite for its function on target protein. Therefore, comprehensive understanding of the physicochemical properties and mechanism behind these complex phenomena is crucial in pharmaceutical research. By using the state-of-art molecular simulations with polarization effect implicitly or explicitly included, we studied the permeation behavior of 2-aminoethoxydiphenyl borate (2-APB), a broad-spectrum modulator for a number of membrane proteins. We showed that the protonation state and therefore the polarity of the drug is critical for its partition, and that the drug is likely to switch between different protonation states along its permeation pathway. By changing the degrees of freedom, protonation further affects the thermodynamic of the permeation pathway of 2-APB, leading to different entropic contributions. A survey on 54 analog structures with similar backbone to 2-APB showed that delicate balance between entropy and polarity plays an important role in drugs’ potency.
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Affiliation(s)
- Qiang Zhu
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China.,Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, P. R. China
| | - Yilin Lu
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China
| | - Xibing He
- School of Pharmacy, University of Pittsburgh, 3501 Terrace Street, Pittsburgh, PA, 15213, USA
| | - Tao Liu
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China
| | - Hongwei Chen
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China
| | - Fang Wang
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China.,College of electronic information engineering, Sanjiang University, Nanjing, 210012, P. R. China
| | - Dong Zheng
- Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, P. R. China
| | - Hao Dong
- Kuang Yaming Honors School, Nanjing University, Nanjing, 210023, P. R. China.
| | - Jing Ma
- Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, P. R. China.
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46
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Ma C, Wang J. Functional studies reveal the similarities and differences between AM2 and BM2 proton channels from influenza viruses. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:272-280. [PMID: 29106970 DOI: 10.1016/j.bbamem.2017.10.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 10/24/2017] [Accepted: 10/25/2017] [Indexed: 11/30/2022]
Abstract
AM2 and BM2 proton channels are attractive antiviral drug targets due to their essential roles during influenza virus replication. Although both AM2 and BM2 are proton-selective ion channels, they share little sequence similarity except for the HXXXW sequence, which suggests that their proton conductance properties might differ. To test this hypothesis, we applied two-electrode voltage clamp electrophysiological assays to study the specific conductance, leakage current, channel activation, and inhibition of AM2 and BM2 proton channels. It was found that BM2 channel has a higher specific conductance than AM2 channel at pH5.5. Unlike AM2 channel, whose proton conductance is asymmetric (from viral exterior to interior), BM2 channel is capable of conducting proton in both directions. Moreover, BM2 requires a more acidic pH for channel activation than AM2, as revealed by its lower pKa values. Finally, both AM2 and BM2 can be inhibited by Cu(II) and Cu(I). Overall, the results from this side-by-side comparison of AM2 and BM2 channels reveal the structure-function relationships of these two viroporins, and such information might be important for the designing of novel ion channels.
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Affiliation(s)
- Chunlong Ma
- BIO5 Institute, The University of Arizona, Tucson, AZ 85721, United States
| | - Jun Wang
- BIO5 Institute, The University of Arizona, Tucson, AZ 85721, United States; Department of Pharmacology and Toxicology, College of Pharmacy, The University of Arizona, Tucson, AZ 85721, United States.
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47
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XFEL structures of the influenza M2 proton channel: Room temperature water networks and insights into proton conduction. Proc Natl Acad Sci U S A 2017; 114:13357-13362. [PMID: 28835537 DOI: 10.1073/pnas.1705624114] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The M2 proton channel of influenza A is a drug target that is essential for the reproduction of the flu virus. It is also a model system for the study of selective, unidirectional proton transport across a membrane. Ordered water molecules arranged in "wires" inside the channel pore have been proposed to play a role in both the conduction of protons to the four gating His37 residues and the stabilization of multiple positive charges within the channel. To visualize the solvent in the pore of the channel at room temperature while minimizing the effects of radiation damage, data were collected to a resolution of 1.4 Å using an X-ray free-electron laser (XFEL) at three different pH conditions: pH 5.5, pH 6.5, and pH 8.0. Data were collected on the Inwardopen state, which is an intermediate that accumulates at high protonation of the His37 tetrad. At pH 5.5, a continuous hydrogen-bonded network of water molecules spans the vertical length of the channel, consistent with a Grotthuss mechanism model for proton transport to the His37 tetrad. This ordered solvent at pH 5.5 could act to stabilize the positive charges that build up on the gating His37 tetrad during the proton conduction cycle. The number of ordered pore waters decreases at pH 6.5 and 8.0, where the Inwardopen state is less stable. These studies provide a graphical view of the response of water to a change in charge within a restricted channel environment.
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48
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Auer S. Simple Model of the Effect of Solution Conditions on the Nucleation of Amyloid Fibrils. J Phys Chem B 2017; 121:8893-8901. [DOI: 10.1021/acs.jpcb.7b05400] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Stefan Auer
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
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49
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Abstract
The 97 amino acid bitopic membrane protein M2 of influenza A forms a tetrameric bundle in which two of the monomers are covalently linked via a cysteine bridge. In its tetrameric assembly the protein conducts protons across the viral envelope and within intracellular compartments during the infectivity cycle of the virus. A key residue in the translocation of the protons is His-37 which forms a planar tetrad in the configuration of the bundle accepting and translocating the incoming protons from the N terminal side, exterior of the virus, to the C terminal side, inside the virus. With experimentally available data from NMR spectroscopy of the transmembrane domains of the tetrameric M2 bundle classical MD simulations are conducted with the protein bundle in different protonation stages in respect to His-37. A full correlation analysis (FCA) of the data sets with the His-37 tetrad either in a fully four times unprotonated or protonated state, assumed to mimic high and low pH in vivo, respectively, in both cases reveal asymmetric backbone dynamics. His-37 side chain rotation dynamics is increased at full protonation of the tetrad compared to the dynamics in the fully unprotonated state. The data suggest that proton translocation can be achieved by decoupled side chain or backbone dynamics. Graphical abstract Visualization of the tetrameric bundle of the transmembrane domains of M2 of influenza A after 200 ns of MD simulations (upper left). The four histidine residues 37 are either not protonated as in M20 or fully protonated is in M24+. The asymmetric dynamics of the backbones are shown after a full correlation analysis (FCA) in blue (lower left). The rotational dynamics of the χ2 dihedral angles of the histidines in M20 (upper right) are less than those in M24+ (lower right).
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Affiliation(s)
- Monoj Mon Kalita
- Institute of Biophotonics and Biophotonics & Molecular Imaging Research Center (BMIRC), School of Biomedical Science and Engineering, National Yang-Ming University, 155, Li-Nong St., Sec. 2, Taipei, 112, Taiwan
| | - Wolfgang B Fischer
- Institute of Biophotonics and Biophotonics & Molecular Imaging Research Center (BMIRC), School of Biomedical Science and Engineering, National Yang-Ming University, 155, Li-Nong St., Sec. 2, Taipei, 112, Taiwan.
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50
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Structural Basis for Asymmetric Conductance of the Influenza M2 Proton Channel Investigated by Solid-State NMR Spectroscopy. J Mol Biol 2017; 429:2192-2210. [PMID: 28535993 DOI: 10.1016/j.jmb.2017.05.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 04/21/2017] [Accepted: 05/16/2017] [Indexed: 12/25/2022]
Abstract
The influenza M2 protein forms an acid-activated proton channel that is essential for virus replication. The transmembrane H37 selects for protons under low external pH while W41 ensures proton conduction only from the N terminus to the C terminus and prevents reverse current under low internal pH. Here, we address the molecular basis for this asymmetric conduction by investigating the structure and dynamics of a mutant channel, W41F, which permits reverse current under low internal pH. Solid-state NMR experiments show that W41F M2 retains the pH-dependent α-helical conformations and tetrameric structure of the wild-type (WT) channel but has significantly altered protonation and tautomeric equilibria at H37. At high pH, the H37 structure is shifted toward the π tautomer and less cationic tetrads, consistent with faster forward deprotonation to the C terminus. At low pH, the mutant channel contains more cationic tetrads than the WT channel, consistent with faster reverse protonation from the C terminus. 15N NMR spectra allow the extraction of four H37 pKas and show that the pKas are more clustered in the mutant channel compared to WT M2. Moreover, binding of the antiviral drug, amantadine, at the N-terminal pore at low pH did not convert all histidines to the neutral state, as seen in WT M2, but left half of all histidines cationic, unambiguously demonstrating C-terminal protonation of H37 in the mutant. These results indicate that asymmetric conduction in WT M2 is due to W41 inhibition of C-terminal acid activation by H37. When Trp is replaced by Phe, protons can be transferred to H37 bidirectionally with distinct rate constants.
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