LIGHT DRIVEN ION TRANSPORT IN BACTERIAL RHODOPSINS

在当前讨论的用于许多离子泵的机制中，访问 在两个膜表面之间交替地有单个结合部位， 依赖于产生能量的反应，而传输的离子是 通过特定的路径往返于该地点。光驱动的 质子和氯离子泵，细菌视紫红质和卤视紫质，是 研究这种全球和局部的机制的理想系统 过程相互作用，以确保离子的单向移动 膜。尽管它的细节是针对这两种细菌的 视紫红质，交替访问机制确定了 可应用于其他离子泵：a)通过小型 活动场地的结构变化，b)控制两个替代方案 局部静电作用下的全球蛋白质构象，c) 通过改变来控制结合亲和力和内离子转移 蛋白质结构域中的介电环境，d)特异性的控制 通过微妙的。离子输运过程中氢键的差异 它的结合位置，以及e)基本参与的偶极性质 结合水存在于离子转移的所有过程中。这项研究 在这个方案中的策略是基于质子和 氯化物相互泵送，最近发现一个单一的氨基 酸替代改变了其中一种的特异性。 这种重组视网膜蛋白将随着时间的推移而被检测- 可见光、红外、x射线的分辨光谱 结晶学和自旋标记探针的性质a)到e)在 为了区分与结合相关的结构和过程，以及 与通道有关的离子的输运导通 结合部位的变化。

In the currently discussed mechanism for many ion pumps, the access of a single binding site alternates between the two membrane surfaces, dependent on an energy-yielding reaction, while the transported ion is conducted to and from this site by specific pathways. The light-driven proton and chloride ion pumps, bacteriorhodopsin and halorhodopsin, are ideal systems to study the mechanism in which such global and local processes interact to ensure the unidirectional movement of the ion across the membrane. Although its details are specific to the two bacterial rhodopsins, the alternating access mechanism identifies principles that may apply to other ion pumps: a) control of local access through small structural changes at the active site, b) control of two alternative global protein conformations through local electrostatic effects, c) control of binding affinity and internal ion transfer through changing dielectric environments in proteins domains, d) control of specificity through subtle. differences in hydrogen bonding of the transported ion at its binding site, and e) essential involvement of the dipole properties of bound water in all processes of the ion translocation. The research strategy in this proposal is based on the similarity of the proton and chloride pumps to one another, and the recent finding that a single amino acid replacement changed the specificity of one into the other. Recombinant retinal proteins of this kind will be examined with time- resolved spectroscopy in the visible and the infrared, x-ray crystallography, and spin-label probes for properties a) through e) in order to distinguish structures and processes relevant to the binding and conduction of the transported ions from those involved in the access change of the binding sites.