Protonation equilibria and pore-opening structure of the dual-histidine influenza B virus M2 transmembrane proton channel from solid-state NMR [Molecular Biophysics]

The influenza A and B viruses are the primary cause of seasonal flu epidemics. Common to both viruses is the M2 protein, a homo-tetrameric transmembrane (TM) proton channel that acidifies the virion after endocytosis. Although influenza A M2 (AM2) and B M2 (BM2) are functional analogs, they have little sequence homology, except for a conserved HxxxW motif, which is responsible for proton selectivity and channel gating. Importantly, BM2 contains a second titratable histidine, His27, in the TM domain, which forms a reverse WxxxH motif with the gating tryptophan. To understand how His27 affects the proton conduction property of BM2, we have used solid-state NMR (SSNMR) to characterize the pH-dependent structure and dynamics of His27. In cholesterol-containing lipid membranes mimicking the virus envelope, 15N NMR spectra show that the His27 tetrad protonates with higher pKa's than His19, indicating that the solvent-accessible His27 facilitates proton conduction of the channel by increasing the proton dissociation rates of His19. AM2 is inhibited by the amantadine class of antiviral drugs while BM2 has no known inhibitors. We measured the N-terminal interhelical separation of the BM2 channel using fluorinated Phe5. The interhelical 19F-19F distances show a bimodal distribution of a short distance of 7 Å and a long distance of 15-20 Å, indicating that the phenylene rings do not block small-molecule entry into the channel pore. These results give insights into the lack of amantadine inhibition of BM2 and reveal structural diversities in this family of viral proton channels.

from # All Medicine by Alexandros G. Sfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2wTJfyT
via IFTTT