%0 Journal Article
%T The counterion¨Cretinylidene Schiff base interaction of an invertebrate rhodopsin rearranges upon light activation
%J -
%D 2019
%R https://doi.org/10.1038/s42003-019-0409-3
%X Animals sense light using photosensitive proteins¡ªrhodopsins¡ªcontaining a chromophore¡ªretinal¡ªthat intrinsically absorbs in the ultraviolet. Visible light-sensitivity depends primarily on protonation of the retinylidene Schiff base (SB), which requires a negatively-charged amino acid residue¡ªcounterion¡ªfor stabilization. Little is known about how the most common counterion among varied rhodopsins, Glu181, functions. Here, we demonstrate that in a spider visual rhodopsin, orthologue of mammal melanopsins relevant to circadian rhythms, the Glu181 counterion functions likely by forming a hydrogen-bonding network, where Ser186 is a key mediator of the Glu181¨CSB interaction. We also suggest that upon light activation, the Glu181¨CSB interaction rearranges while Ser186 changes its contribution. This is in contrast to how the counterion of vertebrate visual rhodopsins, Glu113, functions, which forms a salt bridge with the SB. Our results shed light on the molecular mechanisms of visible light-sensitivity relevant to invertebrate vision and vertebrate non-visual photoreception
%U https://www.nature.com/articles/s42003-019-0409-3