Yan Elsa C Y, Ganim Ziad, Kazmi Manija A, Chang Belinda S W, Sakmar Thomas P, Mathies Richard A
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Biochemistry. 2004 Aug 31;43(34):10867-76. doi: 10.1021/bi0400148.
The vibrational structure of the chromophore in the primary photoproduct of vision, bathorhodopsin, is examined to determine the cause of the anomalously decoupled and intense C(11)=C(12) hydrogen-out-of-plane (HOOP) wagging modes and their relation to energy storage in the primary photoproduct. Low-temperature (77 K) resonance Raman spectra of Glu181 and Ser186 mutants of bovine rhodopsin reveal only mild mutagenic perturbations of the photoproduct spectrum suggesting that dipolar, electrostatic, or steric interactions with these residues do not cause the HOOP mode frequencies and intensities. Density functional theory calculations are performed to investigate the effect of geometric distortion on the HOOP coupling. The decoupled HOOP modes can be simulated by imposing approximately 40 degrees twists in the same direction about the C(11)=C(12) and C(12)-C(13) bonds. Sequence comparison and examination of the binding site suggests that these distortions are caused by three constraints consisting of an electrostatic anchor between the protonated Schiff base and the Glu113 counterion, as well as steric interactions of the 9- and 13-methyl groups with surrounding residues. This distortion stores light energy that is used to drive the subsequent protein conformational changes that activate rhodopsin.
对视觉初级光产物视紫红质中发色团的振动结构进行了研究，以确定异常解耦且强烈的C(11)=C(12)氢面外（HOOP）摇摆模式的成因及其与初级光产物中能量存储的关系。牛视紫红质的Glu181和Ser186突变体的低温（77K）共振拉曼光谱仅显示光产物光谱存在轻微的诱变扰动，这表明与这些残基的偶极、静电或空间相互作用不会导致HOOP模式的频率和强度。进行了密度泛函理论计算，以研究几何畸变对HOOP耦合的影响。通过在C(11)=C(12)和C(12)-C(13)键周围沿相同方向施加约40度的扭曲，可以模拟解耦的HOOP模式。序列比较和结合位点检查表明，这些畸变是由三个限制因素引起的，包括质子化席夫碱与Glu113抗衡离子之间的静电锚定，以及9-甲基和13-甲基与周围残基的空间相互作用。这种畸变存储了光能，用于驱动随后激活视紫红质的蛋白质构象变化。
