Hayashi Shigehiko, Tajkhorshid Emad, Schulten Klaus
Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Biophys J. 2003 Sep;85(3):1440-9. doi: 10.1016/S0006-3495(03)74576-7.
Retinal proteins are photoreceptors found in many living organisms. They possess a common chromophore, retinal, that upon absorption of light isomerizes and thereby triggers biological functions ranging from light energy conversion to phototaxis and vision. The photoisomerization of retinal is extremely fast, highly selective inside the protein matrix, and characterized through optimal sensitivity to incoming light. This article describes the first report of an ab initio quantum mechanical description of the in situ isomerization dynamics of retinal in bacteriorhodopsin, a microbial retinal protein that functions as a light-driven proton pump. The description combines ab initio multi-electronic state molecular dynamics of a truncated retinal chromophore model (N-methyl-gamma-methylpenta-2,4-dieniminium cation fragment) with molecular mechanics of the protein motion and unveils in complete detail the photoisomerization process. The results illustrate the essential role of the protein for the characteristic kinetics and high selectivity of the photoisomerization: the protein arrests inhomogeneous photoisomerization paths and funnels them into a single path that initiates the functional process. Supported by comparison with dynamic spectral modulations observed in femtosecond spectroscopy, the results identify the principal molecular motion during photoisomerization.
视网膜蛋白是在许多生物体内发现的光感受器。它们具有一种共同的发色团——视黄醛，视黄醛在吸收光后会发生异构化，从而触发从光能转换到光趋性和视觉等一系列生物功能。视黄醛的光异构化极其迅速，在蛋白质基质内部具有高度选择性，并以对入射光的最佳敏感性为特征。本文描述了对细菌视紫红质（一种作为光驱动质子泵的微生物视网膜蛋白）中视黄醛原位异构化动力学的从头算量子力学描述的首次报道。该描述将截短的视黄醛发色团模型（N - 甲基 - γ - 甲基戊 - 2,4 - 二烯亚胺阳离子片段）的从头算多电子态分子动力学与蛋白质运动的分子力学相结合，并详细揭示了光异构化过程。结果表明蛋白质对视黄醛光异构化的特征动力学和高选择性起着至关重要的作用：蛋白质阻止不均匀的光异构化路径，并将它们汇聚到一条引发功能过程的单一路径中。通过与飞秒光谱中观察到的动态光谱调制进行比较，结果确定了光异构化过程中的主要分子运动。
