Green-Sensitive, Long-Lived, Step-Functional Anion Channelrhodopsin-2 Variant as a High-Potential Neural Silencing Tool.

Anion channelrhodopsin-2 (GtACR2) was identified from the alga Guillardia theta as a light-gated anion channel, providing a powerful neural silencing tool for optogenetics. To expand its molecular properties, we produced here GtACR2 variants by strategic mutations on the four residues around the retinal chromophore (i.e., R129, G152, P204, and C233). After the screening with the Escherichia coli expression system, we estimated spectral sensitivities and the anion channeling function by using the HEK293 expression system. Among the mutants, triple (R129M/G152S/C233A) and quadruple (R129M/G152S/P204T/C233A) mutants showed the significantly red-shifted absorption maxima (λmax = 498 and 514 nm, respectively) and the long-lived channel-conducting states (the half-life times were 3.4 and 5.4 s, respectively). In addition, both mutants can be activated and inactivated by different wavelengths, representing their step-functional ability. We nicknamed the quadruple mutant "GLaS-ACR2" from its green-sensitive, long-lived, step-functional properties. The unique characteristics of GLaS-ACR2 suggest its high potential as a neural silencing tool.