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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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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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Konstantinidi A, Chountoulesi M, Naziris N, Sartori B, Amenitsch H, Mali G, Čendak T, Plakantonaki M, Triantafyllakou I, Tselios T, Demetzos C, Busath DD, Mavromoustakos T, Kolocouris A. The boundary lipid around DMPC-spanning influenza A M2 transmembrane domain channels: Its structure and potential for drug accommodation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1862:183156. [PMID: 31846647 DOI: 10.1016/j.bbamem.2019.183156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 12/11/2019] [Accepted: 12/12/2019] [Indexed: 10/25/2022]
Abstract
We have investigated the perturbation of influenza A M2TM in DMPC bilayers. We have shown that (a) DSC and SAXS detect changes in membrane organization caused by small changes (micromolar) in M2TM or aminoadamantane concentration and aminoadamantane structure, by comparison of amantadine and spiro[pyrrolidine-2,2'-adamantane] (AK13), (b) that WAXS and MD can suggest details of ligand topology. DSC and SAXS show that at a low M2TM micromolar concentration in DPMC bilayers, two lipid domains are observed, which likely correspond to M2TM boundary lipids and bulk-like lipids. At higher M2TM concentrations, one domain only is identified, which constitutes essentially all of the lipid molecules behaving as boundary lipids. According to SAXS, WAXS, and DSC in the absence of M2TM, both aminoadamantane drugs exert a similar perturbing effect on the bilayer at low concentrations. At the same concentrations of the drug when M2TM is present, amantadine and, to a lesser extent, AK13 cause, according to WAXS, a significant disordering of chain-stacking, which also leads to the formation of two lipid domains. This effect is likely due, according to MD simulations, to the preference of the more lipophilic AK13 to locate closer to the lateral surfaces of M2TM when compared to amantadine, which forms stronger ionic interactions with phosphate groups. The preference of AK13 to concentrate inside the lipid bilayer close to the exterior of the hydrophobic M2TM helices may contribute to its higher binding affinity compared to amantadine.
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Affiliation(s)
- Athina Konstantinidi
- Section of Pharmaceutical Chemistry, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens 15771, Greece
| | - Maria Chountoulesi
- Section of Pharmaceutical Technology, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens 15771, Greece
| | - Nikolaos Naziris
- Section of Pharmaceutical Technology, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens 15771, Greece
| | - Barbara Sartori
- Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9/IV, A-8010 Graz, Austria
| | - Heinz Amenitsch
- Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9/IV, A-8010 Graz, Austria
| | - Gregor Mali
- Department of Inorganic Chemistry and Technology, National Institute of Chemistry, Ljubljana SI-1001, Slovenia
| | - Tomaž Čendak
- Department of Inorganic Chemistry and Technology, National Institute of Chemistry, Ljubljana SI-1001, Slovenia
| | - Maria Plakantonaki
- Department of Chemistry, School of Natural Sciences, University of Patras, Rion, Patras 26500, Greece
| | - Iro Triantafyllakou
- Department of Chemistry, School of Natural Sciences, University of Patras, Rion, Patras 26500, Greece
| | - Theodore Tselios
- Department of Chemistry, School of Natural Sciences, University of Patras, Rion, Patras 26500, Greece
| | - Costas Demetzos
- Section of Pharmaceutical Technology, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens 15771, Greece
| | - David D Busath
- Department of Physiology and Developmental Biology, Brigham Young University, Provo, UT 84602, USA
| | - Thomas Mavromoustakos
- Section of Organic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Athens 15771, Greece.
| | - Antonios Kolocouris
- Section of Pharmaceutical Chemistry, Department of Pharmacy, School of Health Sciences, National and Kapodistrian University of Athens, Athens 15771, Greece.
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Encapsulating Networks of Droplet Interface Bilayers in a Thermoreversible Organogel. Sci Rep 2018; 8:6494. [PMID: 29691447 PMCID: PMC5915452 DOI: 10.1038/s41598-018-24720-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 04/04/2018] [Indexed: 02/08/2023] Open
Abstract
The development of membrane-based materials that exhibit the range and robustness of autonomic functions found in biological systems remains elusive. Droplet interface bilayers (DIBs) have been proposed as building blocks for such materials, owing to their simplicity, geometry, and capability for replicating cellular phenomena. Similar to how individual cells operate together to perform complex tasks and functions in tissues, networks of functionalized DIBs have been assembled in modular/scalable networks. Here we present the printing of different configurations of picoliter aqueous droplets in a bath of thermoreversible organogel consisting of hexadecane and SEBS triblock copolymers. The droplets are connected by means of lipid bilayers, creating a network of aqueous subcompartments capable of communicating and hosting various types of chemicals and biomolecules. Upon cooling, the encapsulating organogel solidifies to form self-supported liquid-in-gel, tissue-like materials that are robust and durable. To test the biomolecular networks, we functionalized the network with alamethicin peptides and alpha-hemolysin (αHL) channels. Both channels responded to external voltage inputs, indicating the assembly process does not damage the biomolecules. Moreover, we show that the membrane properties may be regulated through the deformation of the surrounding gel.
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Ravula T, Hardin NZ, Ramadugu SK, Cox SJ, Ramamoorthy A. Formation of pH-Resistant Monodispersed Polymer-Lipid Nanodiscs. Angew Chem Int Ed Engl 2018; 57:1342-1345. [PMID: 29232017 DOI: 10.1002/anie.201712017] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Indexed: 12/24/2022]
Abstract
Polymer lipid nanodiscs are an invaluable system for structural and functional studies of membrane proteins in their near-native environment. Despite the recent advances in the development and usage of polymer lipid nanodisc systems, lack of control over size and poor tolerance to pH and divalent metal ions are major limitations for further applications. A facile modification of a low-molecular-weight styrene maleic acid copolymer is demonstrated to form monodispersed lipid bilayer nanodiscs that show ultra-stability towards divalent metal ion concentration over a pH range of 2.5 to 10. The macro-nanodiscs (>20 nm diameter) show magnetic alignment properties that can be exploited for high-resolution structural studies of membrane proteins and amyloid proteins using solid-state NMR techniques. The new polymer, SMA-QA, nanodisc is a robust membrane mimetic tool that offers significant advantages over currently reported nanodisc systems.
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Affiliation(s)
- Thirupathi Ravula
- Biophysics Program and Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
| | - Nathaniel Z Hardin
- Biophysics Program and Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
| | - Sudheer Kumar Ramadugu
- Biophysics Program and Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
| | - Sarah J Cox
- Biophysics Program and Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
| | - Ayyalusamy Ramamoorthy
- Biophysics Program and Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109-1055, USA
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Ravula T, Hardin NZ, Ramadugu SK, Cox SJ, Ramamoorthy A. Formation of pH-Resistant Monodispersed Polymer-Lipid Nanodiscs. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201712017] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Thirupathi Ravula
- Biophysics Program and Department of Chemistry; University of Michigan; Ann Arbor MI 48109-1055 USA
| | - Nathaniel Z. Hardin
- Biophysics Program and Department of Chemistry; University of Michigan; Ann Arbor MI 48109-1055 USA
| | - Sudheer Kumar Ramadugu
- Biophysics Program and Department of Chemistry; University of Michigan; Ann Arbor MI 48109-1055 USA
| | - Sarah J. Cox
- Biophysics Program and Department of Chemistry; University of Michigan; Ann Arbor MI 48109-1055 USA
| | - Ayyalusamy Ramamoorthy
- Biophysics Program and Department of Chemistry; University of Michigan; Ann Arbor MI 48109-1055 USA
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