Crystal Structure of the Light-Driven Chloride Pump Halorhodopsin from Natronomonas pharaonis
Crystal Structure of the Light-Driven Chloride Pump Halorhodopsin from Natronomonas pharaonis
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DOI：
10.1016/j.jmb.2009.11.061
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发表时间：
2010-02-26
影响因子：
5.6
通讯作者：
Ihara, Kunio
中科院分区：
文献类型：
--
作者：
Kouyama, Tsutomu;Kanada, Soun;Ihara, Kunio
光驱动的氯离子泵盐视紫红质从嗜盐菌pharaonis（phR）结晶成单斜空间群C2，与phR三聚体每个不对称单元。2.0埃分辨率的衍射数据显示，类胡萝卜素细菌红蛋白结合在三聚体组装中相邻蛋白质亚基之间的缝隙中。除了古细菌视紫红质的七个跨膜螺旋（A至G）之外，phR原聚体在N-末端具有两亲性α-螺旋（A '）。该螺旋与螺旋B和C之间的长环一起形成覆盖细胞外表面的疏水帽，并防止活性中心和细胞外介质之间的快速离子交换。与螺旋G中的Lys 256结合的视黄醛呈现全反式构型，席夫碱与水分子氢键结合。Schiff碱还与Asp 252和氯离子相互作用，后者由螺旋C中的两个极性基团（Thr 126和Ser 130）固定。In.在阴离子摄取途径中，四个可电离残基（Arg 123、Glu 234、Arg 176和His 100）和七个水分子排列形成一个长的氢键网络。相反，细胞质的一半主要是由疏水残基填充，形成一个大的能量屏障，对阴离子的运输。如果细胞质的一半作为质子/HCl反向转运蛋白，这个屏障的高度将大大降低。有趣的是，在螺旋B中，从Lys 25，6的主链羰基延伸到Thr 71存在长的空腔。这种腔，这是常见的盐细菌光驱动的质子泵，是一种可能的途径，用于水介导的质子转移从细胞质介质的阴离子，这是重新定位到细胞质通道在光循环。(C)2009爱思唯尔有限公司保留所有权利。
The light-driven chloride pump halorhodopsin from Natronomonas pharaonis (phR) crystallised into the monoclinic space group C2, with a phR trimer per the asymmetric unit. Diffraction data at 2.0-angstrom resolution showed that the carotenoid bacterioruberin binds to crevices between adjacent protein subunits in the trimeric assembly. Besides seven transmembrane helices (A to G) that characterise archaeal rhodopsins, the phR protomer possesses an amphipathic alpha-helix (A') at the N-terminus. This helix, together with a long loop between helices B and C, forms a hydrophobic cap that covers the extracellular surface and prevents a rapid ion exchange between the active centre and the extracellular medium. The retinal bound to Lys256 in helix G takes on an all-trans configuration with the Schiff base being hydrogen-bonded to a water molecule. The Schiff base also interacts with Asp252 and a chloride ion, the latter being fixed by two polar groups (Thr126 and Ser130) in helix C. In. the anion uptake pathway, four ionisable residues (Arg123, Glu234, Arg176 and His100) and seven water molecules are aligned to form a long hydrogen-bonding network. Conversely, the cytoplasmic half is filled mostly by hydrophobic residues, forming a large energetic barrier against the transport of anion. The height of this barrier would be lowered substantially if the cytoplasmic half functions as a proton/HCl antiporter. Interestingly, there is a long cavity extending from the main-chain carbonyl of Lys25,6 to Thr71 in helix B. This cavity, which is commonly seen in halobacterial light-driven proton pumps, is one possible pathway that is utilised for a water-mediated proton transfer from the cytoplasmic medium to the anion, which is relocated to the cytoplasmic channel during the photocycle. (C) 2009 Elsevier Ltd. All rights reserved.