Abstract
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 photoconvert 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, we showed that vertebrate rhodopsin acquired the photocyclic and photoreversible properties upon introduction of a single mutation at position 188. This revealed that the residue at position 188 contributes to the diversification of photoreaction properties of opsins by its regulation of the recovery from the active state to the original dark state.
Highlights
Opsins are photosensitive G-p rotein-c oupled receptors and are universally found in diploblastic and triploblastic animals
We analyzed a series of mutants at position 188 of bovine rhodopsin and found that G188C mutant has a unique active state which can revert to the original dark state both by a thermal reaction and by a photoreaction
These results showed that the molecular properties of vertebrate rhodopsin can be converted to photocyclic and photoreversible properties by this single mutation
Summary
Opsins are photosensitive G-p rotein-c oupled receptors and are universally found in diploblastic and triploblastic animals. The active state meta II very inefficiently converts back to the original dark state by photoreaction or thermal reaction These observations show that vertebrate rhodopsin is specialized for photoactivation, and is characterized as a monostable opsin. Mollusk and arthropod rhodopsins form a stable active state, the acid-meta state, by photoisomerization of 11-cis to all-trans retinal, and the active state can photoconvert back to the original dark state, which contains 11-c is retinal (Koyanagi and Terakita, 2014; Yau and Hardie, 2009) That is, these opsins have two stable states, the dark and active states, which are interconvertible by light and are known as bistable opsins. G188C mutant of bovine rhodopsin exhibits the photocyclic and photoreversible property and the residue at position 188 regulates the recovery from the active state to the original dark state in vertebrate rhodopsin
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