Microbial rhodopsins: wide distribution, rich diversity and great potential

One of the major topics in biophysics and physicobiology is to understand and utilize biological functions using various advanced techniques. Taking advantage of the photoreactivity of the seven-transmembrane rhodopsin protein family has been actively investigated by a variety of methods. Rhodopsins serve as models for membrane-embedded proteins, for photoactive proteins and as a fundamental tool for optogenetics, a new technology to control biological activity with light. In this review, we summarize progress of microbial rhodopsin research from the viewpoint of distribution, diversity and poten-tial.