c1V1

C1V1 is a chimeric optogenetic actuator used to control neuronal activity with light. It was engineered by fusing the N-terminal region of Channelrhodopsin-1 (C1) with the C-terminal region of Volvox-derived VChR1 (V1), producing a single protein with distinct spectral and kinetic properties compared to other channelrhodopsins.

The spectral profile is shifted toward the green-yellow region, with an activation peak typically reported around 535–550 nm. This red-shift enables deeper tissue illumination and reduces cross-activation when combined with blue-light–sensitive opsins. It forms light-gated cation channels, allowing depolarization upon illumination in mammalian neurons expressing the protein. Kinetics are generally in the millisecond range, though they can vary by construct and expression system; some variants show slower off-kinetics than ChR2, suitable for sustained activation while others have been engineered for faster shutoff.

Applications include optogenetic control of neuronal circuits in vitro and in vivo, elucidating causal relationships between neuronal activity and behavior. It is commonly delivered via viral vectors to targeted brain regions and used in combination with imaging or electrophysiology to assess circuit function.

Variants and derivatives have been developed to tune the spectrum and kinetics, including point mutations and alternative chimeras. C1V1 serves as a representative example of red-shifted channelrhodopsins used to expand the optogenetic toolkit, alongside ChR2, Chrimson, and others.