Structures of the first intermediates of the visual cascade

G蛋白偶联受体(GPCRs)是最大的七螺旋跨膜蛋白家族。它们对跨细胞膜的信号转导至关重要，影响着广泛的生理过程。视紫红质是一种典型的GPCR，在脊椎动物中负责暗视。这也是唯一一个已经确定晶体结构的GPCR，提供了其配体11-顺式视网膜的结构以及它如何与蛋白质匹配的原子细节。阐明配体激发转化为视紫红质激活并与G蛋白偶联的机制可能成为GPCR组其他成员的结构和功能的典范。尽管从视紫红质的静止状态获得了信息，但随后的视觉级联中间体仍然是一个谜。底视紫质是光激发后的直接中间体，其晶体结构存在，但尚未公开。对于Meta-1，已经公布了中低分辨率的低温电子显微镜图像。本建议的目的有三个：通过使用高质量的从头计算方法来验证并在必要时改进已报道的结构，特别是关于配体的构象，在必要和可能的情况下，由经典的力场方法支持；其次，通过对基态和激发态势能表面进行从头计算分子动力学来建立Batho中间体的结构模型。最后，将根据已有的结构和间接证据来开发后续中间体的结构模型。在这些结构的基础上，将在其他项目中研究中间体的性质，并开发动力学模型，以达到对可视级联的初始阶段的全面描述。

G-protein-coupled receptors (GPCRs) constitute the largest family of heptahelical transmembrane proteins. Essential for signal transduction across cell membranes they affect a broad variety of physiological processes. Rhodopsin is a prototypical GPCR which is responsible for scotopic vision in vertebrate species. lt is also the only GPCR for which the crystal structure has been determined providing in atomic detail the structure of its ligand, 11-cis-retinal, and how it fits into the protein. Elucidation of the mechanism, by which ligand excitation is transformed into rhodopsin activation and coupling to the G-protein may become exemplary for the structure and function of other members of the GPCR group.Despite the information gained from the resting state of rhodopsin the ensuing intermediates of the visual cascade remain an enigma. For bathorhodopsin which is the intermediate directly following photoexcitation a crystal structure exists, but has not been made public. For the Meta 1 intermediate low-resolution cryoelectron microscopic images have published. The aim of the present proposal is threefold: verify, and if necessary improve the reported structures, especially with respect to the ligand conformation, by employing high-quality ab initio methods supported, where necessary and possible, by classical force field methods; secondly, develop structural models for the batho intermediate by performing ab initio molecular dynamics an both the ground and the excited state potential energy surfaces. Finally, structural models for the later intermediates will be developed based an the available structures and indirect evidence.On the basis of these structures the properties of the intermediates will be studied in other projects, and dynamical models will be developed to arrive at a comprehensive description of the initial stages of the visual cascade.