The Chemical and Dynamical Influence of the Anti-Viral Drug Amantadine on the M2 Proton Channel Transmembrane Domain

The M2 proton channel plays a vital role in the life cycle of the influenza A virus. His37, the key residue in the M2 transmembrane domain (M2-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 M2 channel. The nuclear spin relaxation data and polarization inversion spin exchange at the magic angle spectra show that both the polypeptide backbone and His37 side chain are more constrained in the presence of amantadine. Using 15N cross polarization magic-angle spinning NMR spectroscopy, the protonation of His37 of M2-TMD in lipid bilayers was monitored in the absence and presence of amantadine as a function of pH. Binding amantadine lowers the His37pKa values by approximately three orders of magnitude compared with the first pKa of histidine in amantadine-free M2-TMD. Amantadine’s influence on the His37 chemical properties suggests a novel mechanism by which amantadine may inhibit proton conductance.