Recent progress in membrane protein dynamics revealed by X-ray free electron lasers: Molecular movies of microbial rhodopsins.

Microbial rhodopsin is a membrane protein with a domain of seven-transmembrane helices and a retinal chromophore. The main function of this protein is to perform light-induced ion transport, either actively or passively, by acting as pumps, channels, and light sensors. It is widely used for optogenetic application to control the activity of specific cells in living tissues by light. Time-resolved serial femtosecond crystallography (TR-SFX) with the use of X-ray free electron lasers is an effective technique for capturing dynamic ion transport and efflux structures across membranes with high spatial and temporal resolutions. Here, we outline recent TR-SFX studies of microbial rhodopsins, including a pump and a channel. We also discuss differences and similarities observed in the structural dynamics derived from the TR-SFX structures.