The Chemical and Dynamical Influence of the Anti-Viral Drug Amantadine on the M 2 Proton Channel Transmembrane Domain

Abstract

The M 2 proton channel plays a vital role in the life cycle of the influenza A virus. His 37, the key residue in the M 2 transmembrane domain (M 2-TMD), plays a central role in the proton conductance mechanism. The anti-influenza drug, amantadine, inhibits the channel activity through binding to the pore of the M 2 channel. The nuclear spin relaxation data and polarization inversion spin exchange at the magic angle spectra show that both the polypeptide backbone and His 37 side chain are more constrained in the presence of amantadine. Using 15N cross polarization magic-angle spinning NMR spectroscopy, the protonation of His 37 of M 2-TMD in lipid bilayers was monitored in the absence and presence of amantadine as a function of pH. Binding amantadine lowers the His 37 pK a values by approximately three orders of magnitude compared with the first pK a of histidine in amantadine-free M 2-TMD. Amantadine’s influence on the His 37 chemical properties suggests a novel mechanism by which amantadine may inhibit proton conductance.