Researchers from the Moscow Institute of Physics and Technology (MIPT), working with colleagues in Spain, France, and Germany, have determined and analyzed the high-resolution structure of a protein from the recently discovered heliorhodopsin family. Microbial rhodopsins play a key role in optogenetics, a technique that involves the introduction of these photosensitive proteins into the membranes of neurons. Left: The dimer of heliorhodopsin 48C12 in the cell membrane (shown as gray discs). Right: High-resolution electron density maps demonstrate the presence of an acetate anion at the active site of heliorhodopsin 48C12. Courtesy of K. Kovalev et al. Genomic studies have led to the discovery of more than 10,000 rhodopsin genes across all three domains of life — bacteria, archaea, and eukaryotes — as well as in giant viruses. Among other things, these proteins are responsible for most of the solar energy captured in the ocean. The diversity, biological significance, and possibilities for the applied use of rhodopsins prompt research into their structure. The researchers analyzed the structure of the 48C12 protein from the heliorhodopsin family in two states and uncovered significant differences between this protein and other known rhodopsins. Although the precise function of heliorhodopsins remains unknown, the researchers hypothesize that the unusual structure and properties of the 48C12 protein could enable it to provide an enzymatic function. Optogenetics, a technique that uses light to control nerve and muscle cells in living tissue, could present new possibilities for treating Parkinson’s disease, depression, anxiety, and epilepsy. The research was published in Proceedings of the National Academy of Sciences (www.doi.org/10.1073/pnas.1915888117).