Molecular basis of spectral tuning in the red- and green-sensitive (M/LWS) pigments in vertebrates

Vertebrate vision is mediated five groups of visual pigments, each absorbing a specific wavelenth of light, between ultraviolet and red. Despite extensive mutagenesis analyses, the mechanisms by which contemporary pigments absorb variable wavelengths of light are poorly understood We show that the molecular bask of the spectral tuning of contemporary visual pigments can be illuminated ouly by mutagenesis analysis using ancestral pigments. Following this new principle, we derive the five-sites rule that explains the absorption spectra of red and green (M/LWS) pigments that range from 510 to 560 nm. Our findings demonstrate that the evolutionary method should be used in elucidating the mechanisms of spectral tuning of four other pigment groups and. for that matter, functional differentiations of any other proteins.