The molecular mechanism for the spectral shifts between vertebrate ultraviolet- and violet-sensitive cone visual pigments

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Abstract
The short-wave-sensitive (SWS) visual pigments of vertebrate cone photoreceptors are divided into two classes on the basis of molecular identity, SWS1 and SWS2. Only the SWS1 class are present in mammals. The SWS1 pigments can be further subdivided into violet-sensitive (VS), with λmax (the peak of maximal absorbance) values generally between 400 and 430nm, and ultraviolet-sensitive (UVS), with a λmaxmax of the goldfish pigment from a wild-type value of 360nm to around 420nm, and the reverse substitution of Tyr-86—Phe into bovine VS opsin produces a similar shift in the opposite direction. The substitution of this single amino acid is sufficient to account therefore for the evolution of bovine and porcine VS pigments. The replacement of Phe with polar Tyr at site 86 is consistent with the stabilization of Schiff-base protonation in VS pigments and the absence of protonation in UVS pigments.