Regulation of phototransduction in short-wavelength cone visual pigments via the retinylidene Schiff base counterion

被引:44
作者
Babu, KR
Dukkipati, A
Birge, RR
Knox, BE
机构
[1] SUNY Upstate Med Univ, Dept Biochem & Mol Biol, Syracuse, NY 13210 USA
[2] SUNY Upstate Med Univ, Dept Ophthalmol, Syracuse, NY 13210 USA
[3] Syracuse Univ, Dept Chem, Syracuse, NY 13244 USA
[4] Syracuse Univ, Dept Biol, Syracuse, NY 13244 USA
关键词
D O I
10.1021/bi015584b
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Short-wavelength visual pigments (SWS1) have lambda (max) values that range from the ultraviolet to the blue. Like all visual pigments, this class has an I I-cis-retinal chromophore attached through a Schiff base linkage to a lysine residue of opsin apoprotein. We have characterized a series of site-specific mutants at a conserved acidic residue in transmembrane helix 3 in the Xenopus short-wavelength sensitive cone opsin (VCOP, lambda (max) similar to 427 nm). We report the identification of D108 as the counterion to the protonated retinylidene Schiff base. This residue regulates the pK(a) of the Schiff base and, neutralizing this charge, converts the violet sensitive pigment into one that absorbs maximally in the ultraviolet region. Changes to tl ris position cause the pigment to exhibit two chromophore absorbance bands, a major band with a lambda (max) of similar to 352-372 nm and a minor, broad shoulder centered around 480 nm. The behavior of these two absorbance bands suggests that these represent unprotonated and protonated Schiff base forms of the pigment. The D108A mutant does not activate bovine rod transducin in the dark but has a significantly prolonged lifetime of the active MetaII state. The data suggest that in short-wavelength sensitive cone visual pigments, the counterion is necessary for the characteristic rapid production and decay of the active MetaII state.
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页码:13760 / 13766
页数:7
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