Steric constraints in the retinal binding pocket of sensory rhodopsin I.
Steric constraints in the retinal binding pocket of sensory rhodopsin I.
复制标题
感觉视紫红质 I 的视网膜结合袋中的空间限制。
DOI：
10.1021/bi00089a044
复制
发表时间：
1993
期刊：
影响因子：
2.9
通讯作者：
Spudich,JL
中科院分区：
文献类型：
--
作者：
Yan,B;Xie,A;Nienhaus,GU;Katsuta,Y;Spudich,JL
摘要：通过研究样品温度和视网膜类似物的影响，分析了感觉视紫红质I （SR-I）视网膜结合袋中的空间约束。在细菌视紫红质（BR）光循环中，最早检测到的中间产物S6io的闪致产率在220 K以下下降，在100 K时达到零，而K的形成与温度无关。低温下S6io形成的减少表明在初级光化学事件中sr - 1的视网膜结合袋更受限制。在四种视网膜类似物中，在视网膜多烯链上引入大体积取代基大大延缓或阻断了sr - 1载脂蛋白与发色团结合的最后一步。除了14-甲基取代外，这些修饰对发色团与BR载子蛋白的结合几乎没有影响。这些结果证实了sr - 1中的视网膜多烯链结合域比BR中的视网膜袋更受空间约束。0-离子环的缺失使类似的sr - 1色素失去功能，13-甲基的缺失也是如此，但相应的BR类似物具有光化学和生理活性。与相应的BR类似物相比，在室温下，用13-去甲基视网膜重组的类似物sr - 1的光解不会产生类似s6io的中间体。上述结果和先前关于蛋白质限制抑制sr - 1中稳定的13-m视网膜结构调节的研究结果表明，13-甲基作为一个支点，允许视网膜一端或两端的运动，以克服异构化的能量障碍。感觉视紫红质I （Sensory rhodopsin I, SR-I）是盐盐杆菌（Halobacterium salinarium，又称H. halobium）膜中的一种趋光受体蛋白（Spudich & Bogomolni, 1988）。光激活其两种光致变色形式SR-I587和S373 (Spudich & Bogomolni, 1984)，使细胞能够迁移到有利于电致离子泵细菌紫质（BR; Oesterhelt et al., 1992; Krebs & Khorana, 1993）和盐紫红质（HR; Lanyi, 1990）光激活的环境中，并逃避有害的紫外线照射。从sr - 1的蛋白序列及其预测的二级结构（black et al., 1989）来看，sr - 1视网膜结合袋与BR有很大（82%）的同源性（Henderson et al., 1990）。对大量类似的SR-I和BR色素的吸收最大值的变化进行了比较，结果与这两种蛋白质中整体同源的视网膜结合结构域基本一致（Yan et al., 1991）。问题是什么结构特征导致了它们不同的功能和不同的光循环动力学。
Revised Manuscript Received June 22, 1993* abstract: Steric constraints in the retinal binding pocket of sensory rhodopsin I (SR-I) are analyzed by studying effects of sample temperature and retinal analogs. The flash-induceid yield of the earliest detected intermediate S6io, which corresponds to the K intermediate in the bacteriorhodopsin (BR) photocycle, decreases below 220 K and reaches zero at 100 K, while K formation is independent of temperature. The reduced S6io formation at low temperatures indicates a more restricted retinal binding pocket in SR-I during primary photochemical events. Introduction of bulky substituents on the retinal polyene chain in four retinal analogs greatly retards or blocks the final step of chromophore binding to the apoprotein of SR-I. Except for the 14-methyl substitution, these modificationsexhibit little or no effect on chromophore binding to BR apoprotein. These results corroborate that the retinal polyene chain binding domain in SR-I is more sterically constrained than that of the retinal pocket in BR. Deletion of the 0-ionone ring renders the analog SR-I pigments nonfunctional, as does deletion of the 13-methyl group, but the corresponding BR analogs are both photochemically and physiologically active. In contrast to the corresponding BR analog, photolysis of the analog SR-I reconstituted with 13-desmethylretinal does not produce an S6io-like intermediate at room temperature. The above results and the previous findings that protein constraints inhibit the accommodation of a stable 13-m-retinal configuration in SR-I suggest a model in which the 13-methyl group functions as a fulcrum to permit movement of one or both ends of retinal to overcome an energy barrier against isomerization.Sensory rhodopsin I (SR-I) is a phototaxis receptor protein in Halobacterium salinarium (also known as H. halobium) membranes (Spudich & Bogomolni, 1988). Light activation of its two photochromic forms, SR-I587 and S373 (Spudich & Bogomolni, 1984), enables cells tomigrate into environments favorable for photoactivation of the electrogenic ion pumps bacteriorhodopsin (BR; Oesterhelt et al., 1992; Krebs & Khorana, 1993) and halorhodopsin (HR; Lanyi, 1990) and escape from damaging UV irradiation. From the protein sequence of SR-Iand its predicted secondary structure (Blanck et al., 1989), a large (82%) homology in the SR-I retinal binding pocket with that of BR is expected (Henderson et al., 1990). Shifts of absorption maxima of a large number of analog SR-I and BR pigments have been compared and generally agree with overall homologous retinal binding structural domains in these two proteins (Yan et al., 1991). The question remains what structural features are responsible for their diverse functions and different photocycle kinetics.