X-ray structure of sensory rhodopsin II at 2.1-Ã… resolution
X-ray structure of sensory rhodopsin II at 2.1-Ã… resolution
复制标题
DOI：
10.1073/pnas.181203898
复制
发表时间：
2001-08-28
影响因子：
11.1
通讯作者：
Navarro, J
中科院分区：
文献类型：
--
作者：
Royant, A;Nollert, P;Navarro, J
感觉视紫红质（SRs）属于含有视网膜发色团的七螺旋跨膜蛋白亚家族。这些光感受器介导动物眼睛的视觉级联反应和古细菌和单细胞鞭毛藻的趋光性。这些光感受器通过换能器蛋白进行信号转导。两种古细菌感觉紫红质SRI和SRII与膜结合的HtrI和HtrII换能器蛋白偶联。这些蛋白的激活启动磷酸化级联反应，调节鞭毛马达，导致引诱剂（SRI）或驱避剂（SRII）趋光性。此外，无换能器的SRI和SRII被证明是质子泵，类似于细菌视紫红质。在这里，我们展示了来自法老钠杆菌（Natronobacterium pharaonis, pSRII）的SRII在2.1埃分辨率下的x射线结构，揭示了视网膜结合口袋的独特分子结构。特别是，pSRII的结构表现出视网膜的很大程度上不弯曲的构象（与细菌视紫红质和盐视紫红质相比），Thr-204的羟基在希夫碱附近，Arg-72的胍基向外取向。此外，该结构揭示了一个假定的氯离子，它通过氢键网络和一个独特的、带正电的表面斑块与希夫碱偶联，可能与HtrII相互作用。pSRII的高分辨率结构为阐明其光导和色彩调节机制提供了结构基础。
Sensory rhodopsins (SRs) belong to a subfamily of heptahelical transmembrane proteins containing a retinal chromophore. These photoreceptors mediate the cascade of vision in animal eyes and phototaxis in archaebacteria and unicellular flagellated algae. Signal transduction by these photoreceptors occurs by means of transducer proteins. The two archaebacterial sensory rhodopsins SRI and SRII are coupled to the membrane-bound HtrI and HtrII transducer proteins. Activation of these proteins initiates phosphorylation cascades that modulate the flagellar motors, resulting in either attractant (SRI) or repellent (SRII) phototaxis. In addition, transducer-free SRI and SRII were shown to operate as proton pumps, analogous to bacteriorhodopsin. Here, we present the x-ray structure of SRII from Natronobacterium pharaonis (pSRII) at 2.1-Angstrom resolution, revealing a unique molecular architecture of the retinal-binding pocket. in particular, the structure of pSRII exhibits a largely unbent conformation of the retinal (as compared with bacteriorhodopsin and halorhodopsin), a hydroxyl group of Thr-204 in the vicinity of the Schiff base, and an outward orientation of the guanidinium group of Arg-72. Furthermore, the structure reveals a putative chloride ion that is coupled to the Schiff base by means of a hydrogen-bond network and a unique, positively charged surface patch for a probable interaction with HtrII. The high-resolution structure of pSRII provides a structural basis to elucidate the mechanisms of phototransduction and color tuning.