The rhodopsin-guanylyl cyclase of the aquatic fungus Blastocladiella emersonii enables fast optical control of cGMP signaling

Blastocladiomycota fungi form motile zoospores that are guided by sensory photoreceptors to optimal light conditions. Here we show that the microbial rhodopsin of Blastocladiella emersonii is a rhodopsin-guanylyl cyclase (RhGC). RhGC is the first member of a new rhodopsin class of light-activated enzymes. Upon light absorption, RhGC (D525) converts in 8 ms after a light flash into a blue-shifted signaling state P380 and recovers within 100 ms. RhGC was well expressed and produced cGMP in response to green light in Xenopus oocytes, CHO cells, and mammalian neurons. Cyclic GMP production was light dose-dependent, rapid and reproducible. Thus, RhGC is a versatile tool for optogenetic analysis of cGMP-dependent signaling processes in cell biology and the neurosciences.