Meeting Abstract
Despite having complex mirror eyes and showing mantle shadow response, the molecular details of scallop light perception have been poorly studied. To unravel the molecular components responsible for light perception in scallop, our lab has assembled transcriptomes from the eyes and mantle tissue of Argopecten irradians. Among other components of the phototransduction pathway, we have identified eleven complete and one incomplete opsin gene sequences from the scallop. We present a detailed molecular and functional characterization of these opsins. All twelve opsins were phylogenetically placed into five major opsin clades, including neuropsin, Go- and Gq-protein coupled opsins, retinochrome, and xenopsin (Gx). Then using a combination of genes isolated from RNA and synthetic genes, we successfully expressed eleven opsins in vitro. Spectral analysis of opsin proteins demonstrates that all are light sensitive. Of the eleven opsins, we quantified the maximum absorbance (lambda max) for four proteins. Six (4 Gq, 1 Go, 1 Gx) opsins form a bistable pigment that can convert its retinal chromophore from the 11-cis to the all trans conformation multiple times. Surprisingly, we found dramatically diverse photochemical properties among the three xenopsins, where two are monostable with a metastate that is blueshifted in a similar manner to vertebrate visual Gt ciliary opsin, while the other is bistable and has a metastate that is redshifted similarly to metamelanopsin. These data show that the diversity of photochemistry for xenopsins/ciliary opsins has been underestimated and is more complex than what can be inferred phylogenetically and open new question on the evolutionary origins of monostable and bistable pigments and their biological role in living systems calling for more functional studies of opsins.
