M2 Proton Channel: Difference between revisions

The M2 channel is low-pH gated and has a 50-fold increase in proton conductance when the pH drops from 8.2 down to 4.2.<ref name="Wu" /> The His side chain, a five-membered ring, has two nitrogen atoms. At a pH of 7 or higher, only one nitrogen is protonated in the neutral imidazole form. However, at a pH of about 5.8, the second nitrogen in one or two helicies becomes protonated and forms the cationic imidazolium form. This protonation causes the His37 residues to move away from each other due to electrostatic repulsion.<ref name="Takeuchi" /><ref name="Lear" /><ref name="Wu" /> The bi-protonated His37 residues are then stabilized by the Trp41 residues by a cation-π interaction. This allows the channel to open and allow water from the pore to penetrate.<ref name="Lear" /> This forms what is called a proton-conductive water wire through the gate.<ref name="Wu" />