PH-driven helix rotations in the inXuenza M2 H⁺ channel: A potential gating mechanism

The pH activated M2 H⁺ channel from inXuenza A has been a subject of numerous studies due to following: (1) It serves as a target for the aminoadamantane drugs that block its channel activity. (2) M2's small size makes it amenable to biophysical scrutiny. (3) A single histidine residue is thought to control the pH gating of the channel. Recent FTIR analysis proposed that the helices of the channel rotate about their directors during pH activation. Herein, we report on molecular dynamics simulations of the X-ray structure of the protein with three charged histidine residues, representing the open form of the protein and two rotated forms with neutral histidines, representing its closed form. We compare the channel stability, convergence, interaction with water and hydration of the histidine residues that have been implicated in channel gating. Taken together, we show that both forms of the protein are stable during the course of the MD simulation and that indeed a rotation of the helices leads to channel closure. Finally, we propose a mechanism for channel gating that involves protonation of the histidine residues that necessities their increased solvation.