Crystal structure of Cruxrhodopsin-3 from Haloarcula vallismortis.
Crystal structure of Cruxrhodopsin-3 from Haloarcula vallismortis.
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DOI：
10.1371/journal.pone.0108362
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发表时间：
2014
期刊：
影响因子：
3.7
通讯作者：
Kouyama T
中科院分区：
文献类型：
--
作者：
Chan SK;Kitajima-Ihara T;Fujii R;Gotoh T;Murakami M;Ihara K;Kouyama T
环视紫红质-3 （cR3）是一种视黄醇蛋白，存在于紫斑藻（Haloarcula vallismortis）的红色膜中，具有光驱动质子泵的功能。本研究采用膜融合法将cR3结晶为空间群P321晶体。2.1 Å分辨率下的衍射数据表明，cR3与菌环蛋白结合在相邻亚基之间的缝隙上形成了三聚体组装体。虽然质子泵送古细菌视紫红质中质子释放途径的结构是保守的，但cR3具有以下特殊的结构特征：1)DE环足够长，可以与邻近的亚基相互作用，加强三聚体组装；2) 3个正电荷分布在螺旋F的细胞质端，影响cR3的高阶结构；3) cR3中视网膜附近的细胞质比细菌视紫红质更坚硬，影响了质子泵循环的早期反应步骤；4)螺旋E的细胞质部分弯曲较大，影响质子摄取过程。同时，我们观察到视网膜的光漂白，在膜状态下很少发生，当cR3的三聚体在过量的洗涤剂存在下解离成单体时变得明显。在此基础上，我们讨论了影响离子泵紫红质光稳定性的结构因素。
Cruxrhodopsin-3 (cR3), a retinylidene protein found in the claret membrane of Haloarcula vallismortis, functions as a light-driven proton pump. In this study, the membrane fusion method was applied to crystallize cR3 into a crystal belonging to space group P321. Diffraction data at 2.1 Å resolution show that cR3 forms a trimeric assembly with bacterioruberin bound to the crevice between neighboring subunits. Although the structure of the proton-release pathway is conserved among proton-pumping archaeal rhodopsins, cR3 possesses the following peculiar structural features: 1) The DE loop is long enough to interact with a neighboring subunit, strengthening the trimeric assembly; 2) Three positive charges are distributed at the cytoplasmic end of helix F, affecting the higher order structure of cR3; 3) The cytoplasmic vicinity of retinal is more rigid in cR3 than in bacteriorhodopsin, affecting the early reaction step in the proton-pumping cycle; 4) the cytoplasmic part of helix E is greatly bent, influencing the proton uptake process. Meanwhile, it was observed that the photobleaching of retinal, which scarcely occurred in the membrane state, became significant when the trimeric assembly of cR3 was dissociated into monomers in the presence of an excess amount of detergent. On the basis of these observations, we discuss structural factors affecting the photostabilities of ion-pumping rhodopsins.
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