Crustaceans as a source of new bistable rhodopsins for optogenetics

Bistable rhodopsins are important for use in the field of optogenetics for controlling neuronal activity by expressing light-activated proteins in neurons. Bistable rhodopsins are useful since two wavelengths can be used to elicit different reactions from one protein. Only a few bistable rhodopsins were characterized so far. Stomatopod crustaceans (a famous member is the peacock mantis shrimp), can detect wavelengths ranging from UV (310 nm wavelength) to infrared (beyond 700 nm) by using different rhodopsins.

A phylogenetic tree comparing a list of ~600 crustacean opsins was created in collaboration with a group of Prof. Porter in Hawaii, and 35 genes were chosen for expression in human cells. Out of chosen genes, 9 have absorption spectra indicative of a well-folded protein. From initial biochemical characterization, we observe a variety of different mechanisms for the action of these opsins. Intriguingly, 5 of these proteins show bistable properties. We found a crustacean rhodopsin belonging to fish louse that can be expressed well in yeast and has interesting properties and is bistable. The wavelengths that activate and deactivate the protein are very far apart, which makes it a potential optogenetic tool in human neurons.