Photocurrent attenuation by a single polar-to-nonpolar point mutation of channelrhodopsin-2.

Channelrhodopsin-2 (ChR2), one of the algal light-gated cation channel rhodopsins, contains five peculiar glutamic acid residues in the N-terminal region corresponding to the second to third transmembrane helices. Here we made systematic mutations of these polar amino acid residues of ChR2 into nonpolar alanine, and evaluated their photocurrent properties. Amongst them, the photocurrent generated by the E97A mutation, ChR2(E97A), was much smaller than expected from its expression. The ChR2(E97A) photocurrent was similar to wild-type ChR2 in the kinetic profiles, the reversal potential and the dependency to the light power density. Our results suggest that the residue E97 is one of the molecular determinants involved in the ion flux regulation.