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.<ref name="Takeuchi" /> At a pH of 7 or higher, only one nitrogen is protonated in the neutral imidazole form.<ref name="Takeuchi" /> However, at a pH of about 5.8, the second nitrogen in one or two helicies becomes protonated and forms the cationic imidazolium form.<ref name="Takeuchi" /> This protonation causes the His residues in each monomer 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.<ref name="Wu" /> This allows the channel to open and allow water from the pore to penetrate.<ref name="Lear" /><ref name="Wu" /> This forms what is called a proton-conductive water wire through the gate.<ref name="Wu" />