pH Dependence of Anabaena Sensory Rhodopsin: Retinal Isomer Composition, Rate of Dark Adaptation, and Photochemistry
pH Dependence of Anabaena Sensory Rhodopsin: Retinal Isomer Composition, Rate of Dark Adaptation, and Photochemistry
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DOI：
10.1021/jp504688y
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发表时间：
2014-07-31
影响因子：
3.3
通讯作者：
Sheves, Mordechai
中科院分区：
文献类型：
--
作者：
Rozin, Rinat;Wand, Amir;Sheves, Mordechai
微生物视紫红质是一种光活性蛋白质，其结合部位可以容纳全反式或13-顺式视网膜发色团。鱼腥藻感觉视紫红质(ASR)是十年前发现的一种微生物视紫红质，其异构体组成、暗适应速率和初级事件的pH依赖关系被提出。主要发现：(A)通过光谱滴定实验观察到两种不同蛋白质残基的pK(A)值分别为6.5和4.0，这两种基态视网膜异构体：全反式，15-抗(AT)和13-顺式，15-syn(13C)。这些蛋白质残基的质子化状态影响色素的吸收光谱，很可能影响视网膜生色团的异构化过程。仅在13C-ASR中观察到额外的pK(A)值8.5。(B)ASR的异构体组成在很宽的pH范围内测定，发现在黑暗中几乎不依赖于pH(>；96%AT异构体)，但在光适应形式下高度依赖于pH。(C)在广泛的pH范围内记录了暗适应的动力学，表明从13C到AT视网膜的热异构化在高pH条件下比在酸性条件下发生得快得多。(D)使用VIS高光谱泵浦探测光谱记录了在pH为5的ASR的主要光化学事件
Microbial rhodopsins are photoactive proteins, and their binding site can accommodate either all-trans or 13-cis retinal chromophore. The pH dependence of isomeric composition, dark-adaptation rate, and primary events of Anabaena sensory rhodopsin (ASR), a microbial rhodopsin discovered a decade ago, are presented. The main findings are: (a) Two pK(a) values of 6.5 and 4.0 assigned to two different protein residues are observed using spectroscopic titration experiments for both ground-state retinal isomers: all-trans, 15-anti (AT) and 13-cis, 15-syn (13C). The protonation states of these protein residues affect the absorption spectrum of the pigment and most probably the isomerization process of the retinal chromophore. An additional pK(a) value of 8.5 is observed only for 13C-ASR. (b) The isomeric composition of ASR is determined over a wide pH range and found to be almost pH-independent in the dark (>96% AT isomer) but highly pH-dependent in the light-adapted form. (c) The kinetics of dark adaptation is recorded over a wide pH range, showing that the thermal isomerization from 13C to AT retinal occurs much faster at high pH rather than under acidic conditions. (d) Primary photochemical events of ASR at pH 5 are recorded using VIS hyperspectral pump probe spectroscopy with