The Photocycle and Proton Translocation Pathway in a Cyanobacterial Ion-Pumping Rhodopsin
The Photocycle and Proton Translocation Pathway in a Cyanobacterial Ion-Pumping Rhodopsin
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DOI：
10.1016/j.bpj.2008.11.026
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发表时间：
2009-02-18
影响因子：
3.4
通讯作者：
Brown, Leonid S.
中科院分区：
文献类型：
--
作者：
Miranda, Mylene R. M.;Choi, Ah Rheum;Brown, Leonid S.
无类囊体蓝藻紫胶杆菌的基因组编码一种能够进行光驱动质子运输的快速循环视紫红质。我们通过光谱表征了 GR 的暗态、光循环和质子易位途径。 GR 的暗状态主要包含全反式视网膜，并且与变形视紫红质类似，不显示明/暗适应。我们发现视网膜的构象与 BR 的 Asp(96) 同源物 Glu(132) 位点之间存在异常强烈的耦合。尽管 GR 的光循环总体上与蛋白视紫红质相似，但其不同之处在于积累了 BR 典型的两种中间体：L 样态和 N 样态。后一种状态具有去质子化的细胞质质子供体，并且在光谱上与已知的原视紫红质的强红移 N 中间体不同。质子吸收先于释放，并发生在向 O 中间体转变期间。 GR 的质子易位途径与其他质子泵视紫红质相似，涉及 BR 希夫碱质子受体和供体 Asp(85) 和 As p(96)（Asp(121) 和 Glu(132)）的同系物。我们将一对 FTIR 谱带（在 1749 cm(-1) 处为正值，在 1734 cm(-1) 处为负值）分别分配给这些羧酸的质子化和去质子化。
The genome of thylakoidless cyanobacterium Gloeobacter violaceus encodes a fast-cycling rhodopsin capable of light-driven proton transport. We characterize the dark state, the photocycle, and the proton translocation pathway of GR spectroscopically. The dark state of GR contains predominantly all-trans-retinal and, similar to proteorhodopsin, does not show the light/dark adaptation. We found an unusually strong coupling between the conformation of the retinal and the site of Glu(132), the homolog of Asp(96) of BR. Although the photocycle of GR is similar to that of proteorhodopsin in general, it differs in accumulating two intermediates typical for BR, the L-like and the N-like states. The latter state has a deprotonated cytoplasmic proton donor and is spectrally distinct from the strongly red-shifted N intermediate known for proteorhodopsin. The proton uptake precedes the release and occurs during the transition to the O intermediate. The proton translocation pathway of GR is similar to those of other proton-pumping rhodopsins, involving homologs of BR Schiff base proton acceptor and donor Asp(85) and As p(96) (Asp(121) and Glu(132)). We assigned a pair of FTIR bands (positive at 1749 cm(-1) and negative at 1734 cm(-1)) to the protonation and deprotonation, respectively, of these carboxylic acids.