3.E.1.7.5
Channel rhodopsin of 829 aas and 7 N-terminal TMSs, KnChR.  Channelrhodopsins (ChRs) are light-gated cation (H⁺, Na⁺, K⁺, and Ca²⁺) channels extensively applied as optogenetics tools for manipulating neuronal activity. All ChRs have a large cytoplasmic domain. The cation channel properties of KnChR from a filamentous terrestrial alga, Klebsormidium nitens, have been described (Tashiro et al. 2021). The C-terminal cytoplasmic domain has a peptidoglycan binding domain (FimV), and modulates the ion channel properties. The channel closure rate is affected by the C-terminus moiety, and truncation of the moiety to various lengths prolongs the channel open lifetime by more than 10-fold. Two Arginine residues (R287 and R291) are crucial for altering the photocurrent kinetics. Tashiro et al. 2021 proposed that electrostatic interaction between the rhodopsin domain and the C-terminal domain accelerates the channel kinetics. Maximal sensitivity was observed at 430 and 460 nm, the former making KnChR one of the most blue-shifted ChRs, serving as a novel prototype for studying the molecular mechanism of color tuning of the ChRs.