An opsin shift in rhodopsin: Retinal S0-S1 excitation in protein, in solution, and in the gas phase
An opsin shift in rhodopsin: Retinal S0-S1 excitation in protein, in solution, and in the gas phase
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DOI：
10.1021/ja0732126
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发表时间：
2007-10-31
影响因子：
15
通讯作者：
Nemulkhin, Alexander
中科院分区：
文献类型：
--
作者：
Bravaya, Ksenia;Bochenkova, Anastasia;Nemulkhin, Alexander
我们考虑了一系列模型系统来处理11-顺式视网膜发色团在真空、溶液和蛋白质环境中的光吸收。在模拟中使用了高计算水平，包括溶液和蛋白质的量子力学-分子力学(QM/MM)方法。采用改进的多组态准简并微扰理论(AUG-MCQDPT2)，在密度泛函理论PBEO/cc-pVDZ近似下优化了基态几何参数，计算了量子子系统的S0-S1激发能.计算得到的气相、溶液和蛋白质的最大吸收峰位置分别为599(G)、448(S)和515(P)nm，与相应的实验值610(G)、445(S)和500(P)nm符合得很好。这种一致性支持了关于生色团几何结构、环境静电场和不同介质中的反离子的作用的定性结论。特别是由于邻近的带电氨基酸残基Glu181的存在，蛋白质在C14-C15键区得到了发色团的基本非平面几何构象。C14-C15键区的非平面性以及负电荷反离子Glu181和GLUL 13的影响被发现对于重现Rh腔内视网膜生色团的光谱特征是重要的。此外，蛋白质场是激发时C11-C12双键最大键级下降的原因，这可能是11-顺式光异构化专一性的原因。
We considered a series of model systems for treating the photoabsorption of the 11-cis retinal chromophore in the protonated Schiff-base form in vacuum, solutions, and the protein environment. A high computational level, including the quantum mechanical-molecular mechanical (QM/MM) approach for solution and protein was utilized in simulations. The S0-S1 excitation energies in quantum subsystems were evaluated by means of anaugmented version of the multiconfigurational quasidegenerate perturbation theory (aug-MCQDPT2) with the ground-state geometry parameters optimized in the density functional theory PBEO/cc-pVDZ approximation. The computed positions of absorption bands lambda(max), 599(g), 448(s), and 515(p) nm for the gas phase, solution, and protein, respectively, are in excellent agreement with the corresponding experimental data, 61 0(g), 445(s), and 500(p) nm. Such consistency provides a support for the formulated qualitative conclusions on the role of the chromophore geometry, environmental electrostatic field, and the counterion in different media. An essentially nonplanar geometry conformation of the chromophore group in the region of the C14-C15 bond was obtained for the protein, in particular, owing to the presence of the neighboring charged amino acid residue Glu181. Nonplanarity of the C14-C15 bond region along with the influence of the negatively charged counterions Glu181 and Glul 13 are found to be important to reproduce the spectroscopic features of retinal chromophore inside the Rh cavity. Furthermore, the protein field is responsible for the largest bond-order decrease at the C11-C12 double bond upon excitation, which may be the reason for the 11-cis photoisomerization specificity.