REMOVAL OF TRANSDUCER HTRI ALLOWS ELECTROGENIC PROTON TRANSLOCATION BY SENSORY RHODOPSIN-I
REMOVAL OF TRANSDUCER HTRI ALLOWS ELECTROGENIC PROTON TRANSLOCATION BY SENSORY RHODOPSIN-I
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DOI：
10.1073/pnas.91.21.10188
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发表时间：
1994-10-11
影响因子：
11.1
通讯作者：
SPUDICH, JL
中科院分区：
文献类型：
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作者：
BOGOMOLNI, RA;STOECKENIUS, W;SPUDICH, JL
感觉视紫红质I（Sensory rhodopsin I，sR-T）是嗜盐菌中的一种趋光性受体，与光驱动质子泵细菌视紫红质和氯离子泵盐视紫红质密切相关。这三种色素经历相似的循环光反应，尽管它们的功能不同。在完整的细胞或分离的膜中，sR-I与信号转导链中的下一个环节蛋白HtrI复合，并且不起生电离子泵的作用。然而，缺乏HtrI的膜中的sR-I的照射导致介质中的pH变化，并且其光反应动力学变得依赖于pH。我们在这里表明，在接近中性pH的封闭囊泡中，它充当生电质子泵，能够产生至少-80mV的跨膜电位。作用光谱显示最大值低于天然色素的587-nm吸收最大值37 nm。出现这种明显的差异是因为587 nm形式的无HtrI的sR-I存在于pH依赖性平衡中，其中550 nm吸收物质是通过一个pK（a）为7.2的基团的去质子化产生的，我们暂时将其确定为Asp-76。我们解释的离子易位的细菌视紫红质的一般模型方面的结果。
Sensory rhodopsin I (sR-T) is a phototaxis receptor in halobacteria, which is closely related to the light-driven proton pump bacteriorhodopsin and the chloride pump halorhodopsin found in the same organisms. The three pigments undergo similar cyclic photoreactions, in spite of their different functions. In intact cells or isolated membranes sR-I is complexed with protein HtrI, the next link in the signal transduction chain, and does not function as an electrogenic ion pump. However, illumination of sR-I in membranes lacking HtrI causes pH changes in the medium, and its photoreaction kinetics become pH-dependent. We show here that in closed vesicles, near neutral pH it functions as an electrogenic proton pump capable of generating at least -80 mV transmembrane potential. The action spectrum shows a maximum 37 nm below the 587-nm absorption maximum of the native pigment. This apparent discrepancy occurs because the 587-nm form of HtrI-free sR-I exists in a pH-dependent equilibrium with a 550-nm absorbing species generated through deprotonation of one group with a pK(a) of 7.2, which we have tentatively identified as Asp-76. We interpret the results in terms of a general model for ion translocation by the bacterial rhodopsins.