The M2 proton channel of Influenza A virus is a tetrameric. A structure of what is known as the conductance domain (residues 22-62) has been characterized by Oriented Sample (OS) and Magic Angle Spinning (MAS) solid state NMR spectroscopy in liquid crystalline lipid bilayers. Here, these new studies utilize the full length M2 protein which has a single transmembrane helix and the key residue for proton selectivity is His37. Near neutral pH these four residues break the four fold symmetry by forming two pairs of imidazole-imidazolium sidechains with a short hydrogen bond where the bridging proton can have a proton chemical shift approaching 20 ppm. These hydrogen-bonded states display remarkable heterogeneity while the backbone does not. The only strong electrostatic interaction between the helices is this pair of hydrogen bonds, the remaining interactions are numerous van der Waals interactions between the helices. Unlike many helical bundles there are no glycine residues that provide a close contact between the helical backbones, instead there are multiple large hydrophobic sidechains that provide much of the hydrophobic inter-helical surface. In MD trajectories different rotomeric states for these hydrophobic sidechains result in changes in the His37 backbone separation of 0.1-0.2 Å. It appears that this heterogeneity accounts for the remarkable distribution of His37 15N and 1H resonance frequencies. Under slightly acidic conditions hydronium ion attack from the external aqueous environment directed toward the less protonated nitrogen of the imidazole-imidazolium pairs results in the breaking of the short hydrogen bond and formation of a pair of imidazolium residues. If a water molecule from the external aqueous environment absorbs one of these imidazolium protons the imidazole-imidazolium pair reforms and a futile cycle has failed to transport a proton to the viral interior. If a water from the interior of the virion captures a proton from one of the two imidazoliums then a conductance cycle results. Recently, we have measured at two different pH values the rate for the conductance cycle from MAS experiments designed to distinguish the rates for the futile and conductance cycles. In addition, we have characterized R and S enantiomers of Rimantadine binding to the M2 channel with a variety of experiments including REDOR measurements and NC correlation experiments using the full length protein.

M2 proton channel: Structure, dynamics and proton exchange data for understanding drug binding and functional rates

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.