Structural guidance of the photocycle of channelrhodopsin-2 by an interhelical hydrogen bond

A postulated hydrogen bond during the mutation of C128 in the transmembrane (TM) helix 3 and D156 in TM helix 4 is used to generate slow mutants of channelrhodopsin-2 (ChR2) and explore their spectral properties of ChR2 which is a light-gated cation channel. The putative hydrogen bond between C128 and D156 is found to be an important structural determinant of the closing reaction in the channel and the D156A mutant is more suitable for light control of excitable cells than C128A.