The Influenza A Virus M2 Channel: A Molecular Modeling and Simulation Study

• Published in: Virology (New York, N.Y.) N.Y.), 1997-06, Vol.233 (1), p.163-173
• Main Authors: Sansom, M.S.P., Kerr, I.D., Smith, G.R., Son, H.S.
• Format: Article
• Language: English
• Subjects: Computer Simulation; Influenza A virus; Influenza A virus - chemistry; Ion Channels - chemistry; Models, Molecular; Molecular Structure; Templates, Genetic; Viral Matrix Proteins - chemistry; Water - chemistry
• ISSN: 0042-6822; 1096-0341
• DOI: 10.1006/viro.1997.8578

The M2 protein of influenza virus forms ion channels activated by low pH which are proton permeable and play a key role in the life cycle of the virus. M2 is a 97-residue integral membrane protein containing a single transmembrane (TM) helix. M2 is present as disulfide-linked homotetramers. The TM domain of M2 has been modeled as a bundle of four parallel M2 helices. The helix bundle forms a left-handed supercoil surrounding a central pore. Residue H37 has been implicated in the mechanism of low-pH activation of the channel. Models generated with H37 in a fully deprotonated state exhibit a pore occluded by a ring of H37 side chains oriented toward the lumen of the pore. Models with H37 in a fully protonated state no longer exhibit such occlusion of the pore, as the H37 side chains adopt a more interfacial location. Extended molecular dynamics simulations with water molecules within and at the mouths of the pores support this distinction between the H37-deprotonated and H37-protonated models. These simulations suggest that only in the H37-protonated model is there a continuous column of water extending the entire length of the central pore. A mechanism for activation of M2 by low pH is presented in which the H37-deprotonated model corresponds to the “closed” form of the channel, while the H37-protonated model corresponds to the “open” form. A switch from the closed to the open form of the channel occurs if H37 is protonated midway through a simulation. The open channel is suggested to contain a wire of H-bonded water molecules which enables proton permeability.