title: Tertiary structure and spectral tuning of UV and violet pigments in vertebrates.
abstract: Many vertebrate species use ultraviolet (UV) vision for such behaviors as mating, foraging, and communication. UV vision is mediated by UV-sensitive visual pigments, which have the wavelengths of maximal absorption (lambda max) at approximately 360 nm, whereas violet (or blue) vision is mediated by orthologous pigments with lambda max values of 390-440 nm. It is widely believed that amino acids in transmembrane (TM) I-III are solely responsible for the spectral tuning of these SWS1 pigments. Recent molecular analyses of SWS1 pigments, however, show that amino acids in TM IV-VII are also involved in the spectral tuning of these pigments through synergistic interactions with those in TM I-III. Comparisons of the tertiary structures of UV and violet pigments reveal that the distance between the counterion E113 in TM III and amino acid sites 87-93 in TM II is narrower for UV pigments than for violet pigments, which may restrict the access of water molecules to the Schiff base pocket and deprotonate the Schiff base nitrogen. Both mutagenesis analyses of E113Q and quantum chemical calculations strongly suggest that unprotonated Schiff base-linked chromophore is responsible for detecting UV light.
authors.affiliation: Department of Biology, Rollins Research Center, Emory University, 1510 Clifton Road, Atlanta, GA 30322, USA. yokoya@emory.edu
authors.forename: Shozo
authors.initials: S
authors.lastname: Yokoyama
authors.forename: William T
authors.initials: WT
authors.lastname: Starmer
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Tada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D018076:DNA, Complementary; D019143:Evolution, Molecular; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D012168:Retinal Pigments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D017299:Rod Opsins / Q000737:chemistry / Q000235:genetics; D012545:Schiff Bases / Q000378:metabolism / Q000528:radiation effects; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014466:Ultraviolet Rays; D014714:Vertebrates / Q000235:genetics / Q000502:physiology*
chemical_list: D018076:DNA, Complementary; D011994:Recombinant Proteins; D012168:Retinal Pigments; D017299:Rod Opsins; D012545:Schiff Bases