Influenza M2 Proteins

Ion channels and transporters provide conduits for the passage of ions and polar compounds across the hydrophobic barrier of lipid membranes. The influenza M2 protein is a low-pH activated proton channel, which acidifies the endosomally trapped virion to cause virus uncoating. Since 2010 it was discovered that M2 also mediates membrane scission in the last step of virus budding and release. The proton-channel function is mostly carried out by the transmembrane domain (TMD) of the protein, whereas the membrane-scission function is conducted by an amphipathic helix C-terminal to the TMD. We investigate the structure and dynamics of M2 bound to phospholipid bilayers to elucidate the mechanisms of proton conduction and membrane scission. The M2 protein of influenza A viruses, which are responsible for all flu pandemics in history, is also the target of one of two classes of antiviral drugs, but currently circulating seasonal flu viruses have evolved drug-resistant mutations. Influenza B virus M2 is so far not druggable, thus structure elucidation of AM2 and BM2 is important for drug development.

Using solid-state NMR, we determine the three-dimensional structures and oligomeric assembly of AM2 and BM2 in lipid bilayers, elucidate proton-transfer equilibria (pKa’s) and kinetics (Fig. 1A), investigate how protein sidechain motions and global motions mediate proton transfer (Fig. 1B), elucidate the drug-binding equilibria (Fig. 1C), and investigate the structures of protein-cholesterol complex (Fig. 1D) and protein-protein complexes. This wealth of information is obtained from chemical shifts, long-range intermolecular distances, and motionally averaged NMR spectra.