Solid-State NMR Investigation of the Conformation, Proton Conduction, and Hydration of the Influenza B Virus M2 Transmembrane Proton Channel

Together with the influenza A virus, influenza B virus causes seasonal flu epidemics. The M2 protein of influenza B (BM2) forms a tetrameric proton-conducting channel that is important for the virus lifecycle. BM2 shares little sequence homology with AM2, except for a conserved HxxxW motif in the transmembrane (TM) domain. Unlike AM2, no antiviral drugs have been developed to block the BM2 channel. To elucidate the proton-conduction mechanism of BM2 and to facilitate the development of BM2 inhibitors, we have employed solid-state NMR spectroscopy to investigate the conformation, dynamics, and hydration of the BM2 TM domain in lipid bilayers. BM2 adopts an α-helical conformation in lipid membranes. At physiological temperature and low pH, the proton-selective residue, His19, shows relatively narrow 15N chemical exchange peaks for the imidazole nitrogens, indicating fast proton shuttling that interconverts cationic and neutral histidines. Importantly, pH-dependent 15N chemical shifts indicate that His19 ret...