Divergent mechanisms for the tuning of shortwave sensitive visual pigments in vertebrates.
Of the four classes of vertebrate cone visual pigments, the shortwave-sensitive SWS1 class shows the shortest lambda(max) values with peaks in different species in either the violet (390-435 nm) or ultraviolet (around 365 nm) regions of the spectrum. Phylogenetic evidence indicates that the ancestral pigment was probably UV-sensitive (UVS) and that the shifts between violet and UV have occurred many times during evolution. This is supported by the different mechanisms for these shifts in different species. All visual pigments possess a chromophore linked via a Schiff base to a Lys residue in opsin protein. In violet-sensitive (VS) pigments, the Schiff base is protonated whereas in UVS pigments, it is almost certainly unprotonated. The generation of VS from ancestral UVS pigments most likely involved amino acid substitutions in the opsin protein that serve to stabilise protonation. The key residues in the opsin protein for this are at sites 86 and 90 that are adjacent to the Schiff base and the counterion at Glu113. In this review, the different molecular mechanisms for the UV or violet shifts are presented and discussed in the context of the structural model of bovine rhodopsin.
Hunt
David M
DM
Institute of Ophthalmology, University College London, Bath Street, London, UK. d.hunt@ucl.ac.uk
Cowing
Jill A
JA
Wilkie
Susan E
SE
Parry
Juliet W L
JW
Poopalasundaram
Subathra
S
Bowmaker
James K
JK
D019943:Amino Acid Substitution; D000818:Animals; D019143:Evolution, Molecular; D006801:Humans; D012168:Retinal Pigments / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D012545:Schiff Bases / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays; D014714:Vertebrates
D012168:Retinal Pigments; D012545:Schiff Bases