Crystal structures of archaerhodopsin-1 and-2: Common structural motif in archaeal light-driven proton pumps
Crystal structures of archaerhodopsin-1 and-2: Common structural motif in archaeal light-driven proton pumps
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DOI：
10.1016/j.jmb.2006.02.032
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发表时间：
2006-05-05
影响因子：
5.6
通讯作者：
Kouyama, T
中科院分区：
文献类型：
--
作者：
Enamil, N;Yoshimura, K;Kouyama, T
古视紫红质-1和-2（aR-1和aR-2）是在盐红菌属（Halorubrum sp.）aus-1和-2中发现的光驱动质子泵，其与盐生盐杆菌（Halobacterium salinarum）中发现的质子泵细菌视紫红质（bR）具有55-58%的序列同一性。在这项研究中，aR-1和aR-2被结晶成属于的3D晶体。分别为P4（3）2（1）2（a = B = 128.1埃，c = 117.6埃）和C222（1）（a = 122.9埃，B = 139.5埃，c = 108.1埃）。每个亚基由七个螺旋片段组成，如在bR中所见，但与bR不同，aR-1以及aR-2在N末端附近具有独特的Ω环。结果发现，在细胞外的一半（即质子释放通道）的质子通路在aR-2中比在aR-1或bR中更开放。这种结构差异解释了三种质子泵之间酸性紫-蓝跃迁的pK（a）的巨大变化。AN的芳族残基周围的视网膜多烯链中保守的三个质子泵，证实了先前的论点，这些残基是所需的立体特异性的视网膜异构化。在细胞质的一半中，螺旋B、C和G包围的区域是高度保守的，而从螺旋E和F挤出的残基的结构保守性非常低。位于质子吸收途径上的疏水残基的结构保守性表明，它们的精确排列是必要的，以防止在大的pH梯度和膜电位的存在下质子的回流。在接触视网膜C13甲基的Leu 93附近通常可见空洞。需要存在这样的空腔，以允许在光循环的早期阶段Leu 93的侧链的大的旋转，这已被证明伴随着水易位通过席夫碱。(c)2006爱思唯尔有限公司保留所有权利。
Archaerhodopsin-1 and -2 (aR-1 and aR-2) are light-driven proton pumps found in Halorubrum sp. aus-1 and -2, which share 55-58% sequence identity with bacteriorhodopsin (bR), a proton pump found in Halobacterium salinarum. In this study, aR-1 and aR-2 were crytallized into 3D crystals belonging. to P4(3)2(1)2 (a = b = 128.1 angstrom, c = 117.6 angstrom) and C222(1) (a = 122.9 angstrom, b = 139.5 angstrom, c = 108.1 angstrom), respectively In both the crystals, the asymmetric unit contains two protein molecules with slightly different conformations. Each subunit is composed of seven helical segments as seen in bR but, unlike bR, aR-1 as well as aR-2 has a unique omega loop near the N terminus. It is found that the proton pathway in the extracellular half (i.e. the proton release channel) is more opened in aR-2 than in aR-1 or bR. This structural difference accounts for a large variation in the pK(a) of the acid purple-to-blue transition among the three proton pumps. AN the aromatic residues surrounding the retinal polyene chain are conserved among the three proton pumps, confirming a previous argument that these residues are required for the stereo-specificity of the retinal isomerization. In the cytoplasmic half, the region surrounded by helices B, C and G is highly conserved, while the structural conservation is very low for residues extruded from helices E and F. Structural conservation of the hydrophobic residues located on the proton uptake pathway suggests that their precise arrangement is necessary to prevent a backward flow of proton in the presence of a large pH gradient and membrane potential. An empty cavity is commonly seen in the vicinity of Leu93 contacting the retinal C13 methyl. Existence of such a cavity is required to allow a large rotation of the sidechain of Leu93 at the early stage of the photocycle, which has been shown to accompany water translocation across the Schiff base. (c) 2006 Elsevier Ltd. All rights reserved.