Creation of photocyclic vertebrate rhodopsin by single amino acid substitution

Opsins are universal photoreceptive proteins in animals and can be classified into three types based on their photoreaction properties. Upon light irradiation, vertebrate rhodopsin forms a metastable active state, which cannot revert back to the original dark state via either photoreaction or thermal reaction. By contrast, after photoreception, most opsins form a stable active state which can photo-convert back to the dark state. Moreover, we recently found a novel type of opsins whose activity is regulated by photocycling. However, the molecular mechanism underlying this diversification of opsins remains unknown. In this study, the molecular property of vertebrate rhodopsin successfully converted to the photocyclic and photoreversible properties by a single mutation at position 188. This revealed that the residue at position 188 contributes to the diversification of photoreaction properties of opsins by the regulation of the recovery from the active state to the original dark state.