Opn5L1 is a retinal receptor that behaves as a reverse and self-regenerating photoreceptor

Abstract

Most opsins are G protein-coupled receptors that utilize retinal both as a ligand and as a chromophore. Opsins’ main established mechanism is light-triggered activation through retinal 11-cis-to-all-trans photoisomerization. Here we report a vertebrate non-visual opsin that functions as a Gi-coupled retinal receptor that is deactivated by light and can thermally self-regenerate. This opsin, Opn5L1, binds exclusively to all-trans-retinal. More interestingly, the light-induced deactivation through retinal trans-to-cis isomerization is followed by formation of a covalent adduct between retinal and a nearby cysteine, which breaks the retinal-conjugated double bond system, probably at the C11 position, resulting in thermal re-isomerization to all-trans-retinal. Thus, Opn5L1 acts as a reverse photoreceptor. We conclude that, like vertebrate rhodopsin, Opn5L1 is a unidirectional optical switch optimized from an ancestral bidirectional optical switch, such as invertebrate rhodopsin, to increase the S/N ratio of the signal transduction, although the direction of optimization is opposite to that of vertebrate rhodopsin.

Localization of the ultraviolet-sensor Opn5m and its effect on myopia-related gene expression in the late-embryonic chick eye

“…There are three Opn5 subfamily members in Gallus gallus [3,8,19,20], and we focused on Opn5m as it was the most prominent Opn5 receptor in the chicken embryonic retina and is also present in mammals. Reverse transcription PCR analysis showed that Opn5m was expressed in the cornea and sclera of E17 chicken embryos (Fig.…”

Ultrafast pulse shaping modulates perceived visual brightness in living animals

“…Notice that reverse photoisomerization of the visual rhodopsin is usually assumed to be impossible in natural illumination conditions ( 22 , 23 ). This is definitely the case when the whole protein complex has relaxed in its final conformation (milliseconds) via the well-known photo, batho, lumi, and meta intermediates ( 22 ).…”

Reverse optogenetics of G protein signaling by zebrafish non-visual opsin Opn7b for synchronization of neuronal networks

“…Binding of all-trans-retinal to Opn5L1 stabilizes the active state of the GPCR and therefore G protein activation. Absorption of photons leads to a trans-cis isomerization of the retinal compound, causing GPCR inactivation followed by the slow self-regeneration to the active state in the dark 18 . Therefore, the activation-inactivation-reactivation cycle observed for Opn7b modulated GIRK currents resemble the reverse action of Opn5L1.…”