Proton translocation mechanism and energetics in the light-driven pump bacteriorhodopsin.
Proton translocation mechanism and energetics in the light-driven pump bacteriorhodopsin.
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光驱动泵细菌视紫红质中的质子易位机制和能量学。
DOI：
10.1016/0005-2728(93)90226-6
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Lanyi,JK
中科院分区：
文献类型：
--
作者：
Lanyi,JK
细胞和细胞器中产生质子跨膜电化学电势的各种离子泵以各种方式驱动：化学反应过程中底物结合能的变化（离子型ATP酶和NADH/NADP转氢酶），光激发后和氧化还原反应期间的电子转移（光合反应中心，细胞色素氧化酶和细胞色素bc复合物），或直接通过pK a变化引起的视网膜光依赖性键旋转（细菌视紫红质）。最后一个是最简单的。它基于容易可视化的酸碱反应，所需的可能只是最小的可想象的功能性跨膜蛋白。细菌视紫红质是一种最为人所知的离子泵，它已经成为研究膜蛋白跨膜核心结构和质子转运系统内部工作的典范。细菌视紫红质是一种完整的膜蛋白（26 kDa），其7个跨膜螺旋片段（AG）包围了全反式视网膜发色团的结合口袋[76]，通过质子化席夫碱与螺旋G中心附近的K216结合，并从膜平面倾斜约20 [79，99]。由该蛋白质的三聚体组成的天然存在的扩展的二维六边形晶格（“紫色膜”）使得有可能以3.5-7 A的分辨率确定其三维电子密度图[12，76，77]。根据该图谱以及一级和预测的二级结构，构建了具有接近原子分辨率的结构模型[76]。虽然确切的空间处置的一些残留物，特别是在膜表面，仍然是不确定的，这个模型是所有试图描述的运输机制的出发点。细菌视紫红质的光照启动了一个多步反应循环，该反应循环从13-反式-15-反式构型（“光适应”发色团）到13-顺式-15-反式构型的视黄醛异构化开始[6，22]，并通过一系列热步骤进行，使质子跨膜移位。光谱的变化已经确定了当这种“光循环”在低温下被阻止时在光稳态中积累的中间体（例如参考文献1）。15，102，164）。光激发与光脉冲短于寿命的中间状态使得有可能遵循这些国家的相互转换在环境温度下，并在一个单一的营业额（例如，参考文献。4、21、64，118，195，200）。在这些研究中，通过各种光谱方法，包括可见光、UV、共振拉曼、FTIR和NMR光谱法，以及用类似物替换retinal，描述了retinal及其构型转化，而通过FTIR和UV光谱法以及利用位点特异性残基替换的研究，揭示了蛋白质的变化。蛋白质和散装之间的质子交换的时程已经遵循，反过来，使用pH指示剂染料和光电测量。在过去的几年中，大量的工作利用这些方法牢固地建立了质子传输的基本要素。这篇综述的目的是从不同的发现中组装一个连贯的机械和热力学模型，并指出哪些信息缺失或出现矛盾。特别强调的是放在那些残基的相互作用，细菌视紫红质，调节质子亲和力沿着易位的途径，因为这些应该是相关的质子泵一般。有关细菌视紫红质和其他细菌视紫红质的更多信息，以及...
The various ion pumps in cells and organelles that generate transmembrane electrochemical potential for protons are driven in various ways: changes in substrate-binding energy during chemical reactions (ionmotive ATPases and NADH/NADP transhydrogenase), electron transfer after photoexcitation and during redox reactions (photosynthetic reaction centers, cytochrome oxidase and the cytochrome bc-com-plex), or directly through pK a changes set off by lightdependent bond-rotations in retinal (bacteriorhodopsin). The last of these is the simplest. It is based on easily visualized acid-base reactions that require no more than what is probably the smallest imaginable functional membrane-spanning protein. Bacteriorhodopsin, the best understood ionic pump, has become the paradigm for both the structure of the transmembrane core of membrane proteins and the internal workings of proton transport systems. Bacteriorhodopsin is an integral membrane protein (26 kDa) whose seven transmembrane helical segments (AG) enclose a binding pocket for the all-trans-retinal chromophore [76], bound via a protonated Schiff base to K216 near the center of helix G and inclined about 20 [79, 99] from the plane of the membrane. A naturally occurring extended two-dimensional hexagonal lattice ('purple membrane') comprised of trimers of this protein has made it possible to determine its three-dimensional electron density map at 3.5-7 A resolution [12, 76, 77]. From this map and the primary and predicted secondary structures, a structural model with nearly atomic resolution was constructed [76]. Although the exact spatial dispositions of some of the residues, particularly at the membrane surfaces, are still uncertain, this model is the point of departure for all attempts to describe the transport mechanism. Illumination of bacteriorhodopsin initiates a multistep reaction cycle that begins with isomerization of the retinal from the 13-trans-15-anti configuration (the'light-adapted'chromophore) to 13-cis-15-anti [6, 22], and proceeds through a series of thermal steps that translocate a proton across the membrane. Spectroscopic changes have identified the intermediates that accumulate in photostationary states when this' photocycle'is arrested at cryogenic temperatures (eg Refs. 15,102,164). Photoexcitation with light pulses shorter than the lifetimes of the intermediate states made it possible to follow the interconversions of these states at ambient temperature and during a single turnover (eg, Refs. 4, 21, 64,118,195,200). The retinal and its configurational transformations have been described in such studies by a variety of spectroscopic methods, including visible, UV, resonance Raman, FTIR, and NMR spectroscopy, and replacement of the retinal with analogues, while changes in the protein have been revealed by FTIR and UV spectroscopy and by studies utilizing site-specific residue replacements. The timecourse of proton exchange between the protein and the bulk has been followed, in turn, using pH-indicator dyes and photoelectric measurements. During the last few years a considerable body of work utilizing these approaches firmly established the basic elements of the proton transport. The purpose of this review is to assemble a coherent mechanistic and thermodynamic model from the diverse findings, and to indicate what information is missing or appears contradictory. Particular emphasis is placed on those residue interactions in bacteriorhodopsin that modulate proton affinities along the pathway of translocation because these should be relevant for proton pumps in general. For additional information on bacteriorhodopsin and other bacterial rhodopsins, as well as …