Proton circulation during the photocycle of sensory rhodopsin II.
Proton circulation during the photocycle of sensory rhodopsin II.
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DOI：
10.1016/s0006-3495(99)77055-4
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发表时间：
1999-10
影响因子：
3.4
通讯作者：
J. Sasaki;J. Spudich
中科院分区：
文献类型：
--
作者：
J. Sasaki;J. Spudich
盐生盐杆菌膜上的感觉视紫红质II（Sensory Rhodopsin II，SRII）是一种趋光性受体，通过与其结合的传感器HtrII发出信号以避开蓝绿光。在本研究中，我们研究了质子运动过程中的光循环的SRII在HtrII的自由和HtrII络合的形式。我们监测持续的光诱导的pH值的变化与pH电极，和激光闪光诱导的pH值的变化与pH值指示剂吡喃使用密封的膜囊泡和开放的片含有自由或复合受体。结果表明，SRII在M到O的转换中吸收一个质子，并在O衰变过程中释放它。摄取和释放是从细胞外侧和向细胞外侧的，因此SRII不将质子转运穿过膜。SRII光循环的pH依赖性表明在细胞外质子传导路径中存在可质子化基团（pKa ≤ 7.5），其在M-至-O转换中由Schiff碱在质子吸收中起作用。由SRII产生的细胞外质子循环不被HtrII络合所阻断，不像在同一系列测量中发现的被其换能器HtrI阻断的SRI中的细胞质质子传导。这一发现的影响，目前的模型SRI和SRII信号进行了讨论。
Sensory rhodopsin II (SRII) inHalobacterium salinarummembranes is a phototaxis receptor that signals through its bound transducer HtrII for avoidance of blue-green light. In the present study we investigated the proton movements during the photocycle of SRII in the HtrII-free and HtrII-complexed form. We monitored sustained light-induced pH changes with a pH electrode, and laser flash-induced pH changes with the pH indicator pyranine using sealed membrane vesicles and open sheets containing the free or the complexed receptor. The results demonstrated that SRII takes up a proton in M-to-O conversion and releases it during O-decay. The uptake and release are from and to the extracellular side, and therefore SRII does not transport the proton across the membrane. The pH dependence of the SRII photocycle indicated the presence of a protonatable group (pKa∼7.5) in the extracellular proton-conducting path, which plays a role in proton uptake by the Schiff base in the M-to-O conversion. The extracellular proton circulation produced by SRII was not blocked by HtrII complexation, unlike the cytoplasmic proton conduction in SRI that was found in the same series of measurements to be blocked by its transducer, HtrI. The implications of this finding for current models of SRI and SRII signaling are discussed.