A Conserved Aromatic Residue Regulating Photosensitivity in Short-Wavelength Sensitive Cone Visual Pigments

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• 作者：Colleen M. Kuemmel ; Megan N. Sandberg ; Robert R. Birge ; Barry E. Knox
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：July 30, 2013
• 年：2013
• 卷：52
• 期：30
• 页码：5084-5091
• 全文大小：446K
• 年卷期：v.52,no.30(July 30, 2013)
• ISSN：1520-4995

文摘

Visual pigments have a conserved phenylalanine in transmembrane helix 5 located near the 尾-ionone ring of the retinal chromophore. Site-directed mutants of this residue (F207) in a short-wavelength sensitive visual pigment (VCOP) were studied using UV鈥搗isible spectroscopy to investigate its role in photosensitivity and formation of the light-activated state. The side chain is important for pigment formation: VCOP^F207A, VCOP^F207L, VCOP^F207M, and VCOP^F207W substitutions all bound 11-cis-retinal and formed a stable visual pigment, while VCOP^F207V, VCOP^F207S, VCOP^F207T, and VCOP^F207Y substitutions do not. The extinction coefficients of all pigments are close, ranging between 35800 and 45600 M^鈥? cm^鈥?. Remarkably, the mutants exhibit an up to 5-fold reduction in photosensitivity and also abnormal photobleaching behavior. One mutant, VCOP^F207A, forms an isomeric composition of the retinal chromophore after illumination comparable to that of wild-type VCOP yet does not release the all-trans-retinal chromophore. These findings suggest that the conserved F207 residue is important for a normal photoactivation pathway, formation of the active conformation and the exit of all-trans-retinal from the chromophore-binding pocket.