Structural Biology of Sensory Rhodopsin

描述(申请人提供)：感觉受体视网膜结合蛋白是光信号转导的主要介体。最具特性的跨膜感觉受体是视紫红质，一种G蛋白偶联受体超家族的范例，以及来自嗜盐古细菌的感觉视紫红质II。视紫红质使用光触发级联反应的初始步骤，最终形成视觉，而感官视紫红质II使用光启动磷酸化级联反应，调节细胞的鞭毛马达，以控制趋光性。最近，我们阐明了SRII的晶体结构，分辨率达到2.1A，使我们现在能够阐明光信号转导的机制。此外，在一项并行的计算工作中，我们确定了调节颜色调节的物理决定因素。然而，SRII在基态的这种结构只代表了一个复杂的反应途径的一个步骤，该反应始于光激发，随后是受体的构象变化，并将光信号传递给同源蛋白质。显然，为了完全理解SRII介导的感觉信号传递机制，我们需要深入了解这一信号通路上中间体的原子结构，以及SRII-HtrII复合体的结构。这个项目解决了一个基本的问题：视网膜光异构化如何触发蛋白质结构变化，从而导致转导通路的激活，从而启动感觉反应？回答这个问题对于阐明感觉受体介导的信号转导的分子机制至关重要。本项目的目的是通过捕获和解析1)K-和2)M-中间体的结构，识别SRII中最终导致受体信号状态形成的结构运动，3)通过解析SRII-HtrII基态复合体的X射线结构，阐明SRII识别和结合其同源转导蛋白的机制，以及4)通过解析其X射线结构，确定感觉性视紫红质I的结构决定因素。实现这些特定的目标应该使我们最终能够以高分辨率阐明感觉性视紫红质介导的信号的分子机制。预计它们将与视觉视紫质相似，因此与对视觉在健康和疾病中的机制的分子理解有关。

DESCRIPTION (provided by applicant): Sensory receptor retinal-binding proteins are major mediators in light signal transduction. The best characterized transmembrane sensory receptors are rhodopsin, a paradigm of the G protein-coupled receptor superfamily, and sensory rhodopsin II from halophilic archeabacteria. Rhodopsin uses light to trigger the initial steps in a cascade that culminates in vision, while sensory rhodopsin II uses light to initiate a phosphorylation cascade that regulates the cell's flagellar motors in order to control phototaxis. We very recently elucidated the crystal structure of SRII to 2.1 A resolution, allowing us now to elucidate the mechanisms of light signal transduction. Moreover, in a parallel computational work, we identified the physical determinants that regulate color tuning. However, this structure of SRII in the ground state represents only a single step along a complex reaction pathway, which starts with photoexcitation, followed by conformational changes of the receptor, and transmission of the light signal to cognate proteins. Clearly, to fully understand the mechanism of sensory signaling mediated by SRII we require insight into the atomic structures of the intermediates along this signaling pathway, as well as the structure of the SRII-HtrII complex. This project addresses a fundamental question: How does retinal photoisomerization trigger protein structural changes that lead to activation of the transducer, thereby initiating the sensory response?Answering this question is essential for elucidating the molecular mechanisms of signal transduction mediated by sensory receptors. The aims of this project are to identify the structural movements in SRII that culminate in the formation of the signaling state of the receptor, by trapping and solving the structures of the 1) K- and 2) M-intermediates, 3) elucidate the mechanism by which SRII recognizes and binds its cognate transducer protein, by solving the X-ray structure of the ground-state SRII-HtrII complex, and 4) identify the structural determinants of sensory rhodopsin I, which can act as a photoattractant and photorepellent, by solving its X-ray structure. Achieving these Specific Aims should allow us finally to elucidate, at high resolution the molecular mechanisms of sensory rhodopsin-mediated signaling. These are expected to be similar to that of visual rhodopsin, and so relevant to a molecular understanding of the mechanism of vision in health and disease.