Bioorganic Studies of Retinal Proteins in Halobacterium halobium (Chemistry)

在某些细菌膜中发现的色素，其化学性质与动物视觉化学中使用的色素惊人地相似。细菌色素显然与人眼中发现的相应色素具有截然不同的功能。然而，这两个体系中的一些基本反应在本质上是非常相似的。本项目隶属于有机和大分子化学专业，旨在研究这些细菌色素生物功能的基本化学性质。至少有三种以视网膜为发色团的膜蛋白已从古盐杆菌中分离出来：细菌视紫红质（bR）将质子泵过膜，盐视紫红质（hR）将氯离子转运过膜，感觉视紫红质（sR）负责嗜盐菌的致光行为。由于细菌是在浓氯化钠溶液中生长的，不太担心受到污染，而且上述色素属于最简单的膜蛋白，因此它们非常适合研究膜相关现象。因此，这些颜料引起了各个科学学科的广泛兴趣。目的是在分子结构基础上研究色素功能的机制，方法是研究与各种合成视黄醛和/或标记氨基酸结合的色素类似物。主要目标是：(i)通过光亲和标记等方法测定bR的三级结构；（ii）描述bR中质子泵送所需的显色基团的结构因素；（iii）澄清bR内发生的导致质子转移的事件顺序。与sR和hR相关的研究也将进行。傅里叶变换红外（FTIR）差分光谱以及其他光谱技术将被使用。这样的研究将有助于我们对膜运输的理解，这是一个中心但很少被理解的主题。

Pigments found in the membranes of certain bacteria are of a chemical nature surprisingly like that of pigments employed in the chemistry of vision in animals. The bacterial pigments clearly have a much different function than do the corresponding pigments found in the human eye. However, some of the fundemental reactions in both systems are very similar in nature. This project in the Organic and Macromolecular Chemistry Program is designed to investigate the basic chemistry of the biological function of these bacterial pigments. At least three membrane proteins possessing retinal as the chromophore have been isolated from the ancient bacterium Halobacterium halobium: bacteriorhodopsin (bR) which pumps protons across the membrane, halorhodopsin (hR) which translocates chloride ions across the membrane, and sensory rhodopsin (sR) which is responsible for the phototactic behavior of H. halobium. Because the bacteria are grown in concentrated sodium chloride solution without much fear of contamination, and because the above-mentioned pigments are among the simplest of membrane proteins, they are ideally suited for studying membrane related phenomena. The pigments are thus attracting wide interest from the various scientific disciplines. The objective is to investigate the mechanism of the pigment functions on a molecular structural basis, the approach being studies on pigment analogs that have been incorporated with various synthetic retinals and/or labeled amino acids. The main targets are: (i) determination of the tertiary structure of bR by photoaffinity labeling and other means; (ii) delineation of structural factors of the chromophoric moiety required for proton pumping in bR; and (iii) clarification of the sequence of events occurring within bR leading to the transfer of protons. Related studies with sR and hR will also be performed. Fourier transform infrared (FTIR) difference spectroscopy as well as other spectroscopic techniques will be used. Such studies will contribute to our understanding of membrane transport, a central but little understood theme.