Color Tuning in Bovine Rhodopsin through Polarizable Embedding

Bovine rhodopsin is among the most studied proteins in the rhodopsin family. Its primary activation mechanism is the photoisomerization of 11-cis retinal, triggered by the absorption of a UV–visible photon. Different mutants of the same rhodopsin show different absorption wavelengths due to the influence of the specific amino acid residues forming the cavity in which the retinal chromophore is embedded, and rhodopsins activated at different wavelengths are, for example, exploited in the field of optogenetics. In this letter, we present a procedure for systematically investigating color tuning in models of bovine rhodopsin and a set of its mutants embedded in a membrane bilayer. Vertical excitation energy calculations were carried out with the polarizable embedding potential for describing the environment surrounding the chromophore. We show that polarizable embedding outperformed regular electrostatic embedding in determining both the vertical excitation energies and associated oscillator strengths of the systems studied.

牛视紫红质（Bovine rhodopsin）是视紫红质家族中研究最为广泛的蛋白质之一。其核心激活机制为11-顺式视黄醛的光异构化过程，该过程由紫外-可见光子的吸收所触发。同一视紫红质的不同突变体，因构成视黄醛生色团所处空腔的特定氨基酸残基的影响，会呈现出不同的吸收波长；而可在不同波长下激活的视紫红质，已在光遗传学（optogenetics）领域得到应用。在本研究快报中，我们提出了一套可系统探究牛视紫红质及其嵌入膜双层的一系列突变体模型颜色调谐特性的研究方法。本研究采用极化嵌入势（polarizable embedding potential）描述生色团周围的环境，并以此开展垂直激发能（vertical excitation energy）计算。结果表明，在计算所研究体系的垂直激发能及其对应的振子强度（oscillator strengths）时，极化嵌入势的性能优于常规静电嵌入（electrostatic embedding）。