Functional, Dynamic and Structural Understanding of M2 Proton Channel from Influenza A and its Inhibition

Abstract

While it has long been agreed that the M2 proton channel functions by shuttling protons on and off of the histidine tetrad near the mid plane of the lipid bilayer, the details have been hotly debated. Now details of the shuttling mechanism have been elucidated from solid state NMR spectroscopy. Short hydrogen bonds between the imidazole-imidazolium pairs are confirmed as well as their disruption by aqueous attack followed by N-H exchange and imidazolium-imidazole hydrogen bond reformation by either a deprotonation to the aqueous pore connected to the viral external environment (a futile proton cycle) or by deprotonation to a waters in the internal cavity between the His37 and Trp41 tetrads. For this latter option when the Trp41 gate opens the proton can be conducted into the viral interior (conductance cycle). The dynamics of the Trp41 residues and those of the secondary conductance gate (Val27) have been evaluated by wide-line solid state NMR.Solid state NMR REDOR and NCA experiments of the full length wild type M2 channel in complex with rimantadine enantiomers. The binding of these enantiomers to M2 shows a difference in binding affinity and a different set of binding interactions implying that stereospecific drugs may have biomedical benefits.M2 has multiple functions, among them is the facilitation of viral budding that takes advantage of the pyramidal shape of the M2 structure to induce membrane curvature. This shape is caused by the insertion of the juxtamembrane amphipathic helix in the lipid bilayer interface. We have now shown that the stability of this helix in the membrane is the result of cholesterol binding to this helix.