Characterization of the Mutant Visual Pigment Responsible for Congenital Night Blindness: A Biochemical and Fourier-Transform Infrared Spectroscopy Study

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• 作者：Tatyana A. Zvyaga ; Karim Fahmy ; Friedrich Siebert ; and Thomas P. Sakmar
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：June 11, 1996
• 年：1996
• 卷：35
• 期：23
• 页码：7536 - 7545
• 全文大小：373K
• 年卷期：v.35,no.23(June 11, 1996)
• ISSN：1520-4995

文摘

A mutation in the gene for the rod photoreceptor moleculerhodopsin causes congenital nightblindness. The mutation results in a replacement ofGly⁹⁰ by an aspartic acid residue. Twomolecularmechanisms have been proposed to explain the physiology of affected rodcells. One involves constitutiveactivity of the G90D mutant opsin [Rao, V. R., Cohen, G. B., & Oprian,D. D. (1994) Nature 367, 639-642]. A second involves increased photoreceptor noise caused bythermal isomerization of the G90Dpigment chromophore [Sieving, P. A., Richards, J. E., Naarendorp, F.,Bingham, E. L., Scott, K., &Alpern, M. (1995) Proc. Natl. Acad. Sci.U.S.A. 92, 880-884]. Based onexisting models of rhodopsinand in vitro biochemical studies of site-directed mutants,it appears likely that Gly⁹⁰ is in theimmediateproximity of the Schiff base chromophore linkage. We have studiedin detail the mutant pigments G90Dand G90D/E113A using biochemical and Fourier-transform infrared (FTIR)spectroscopic methods. Thephotoproduct of mutant pigment G90D, which absorbs maximally at 468 nmand contains a protonatedSchiff base linkage, can activate transducin. However, the activephotoproduct decays rapidly to opsinand free all-trans-retinal. FTIR studies of mutant G90Dshow that the dark state of the pigment hasseveral structural features of metarhodopsin II, the active form ofrhodopsin. These include a protonatedcarboxylic acid group at position Glu¹¹³ and increasedhydrogen-bond strength of Asp⁸³. Additionalresults,which relate to the structure of the active G90D photoproduct, are alsoreported. Taken together, theseresults may be relevant to understanding the molecular mechanism ofcongenital night blindness causedby the G90D mutation in human rhodopsin.