Protein, lipid and water organization in bacteriorhodopsin crystals:: a molecular view of the purple membrana at 1.9 Å resolution
Protein, lipid and water organization in bacteriorhodopsin crystals:: a molecular view of the purple membrana at 1.9 Å resolution
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DOI：
10.1016/s0969-2126(99)80118-x
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发表时间：
1999-08-15
期刊：
影响因子：
5.7
通讯作者：
Pebay-Peyroula, E
中科院分区：
文献类型：
--
作者：
Belrhali, H;Nollert, P;Pebay-Peyroula, E
背景：盐盐杆菌中的细菌视紫红质（bR）是一种质子泵，将光能转化为质子梯度，驱动ATP合成。该蛋白由7个跨膜螺旋组成，在体内被组织成紫色斑块，其中bR和脂质形成晶体二维阵列。吸收光子后，通过席夫碱与Lys216共价结合的视网膜被异构化为13-顺，15-反构型。这引发了一系列事件——光循环——在此过程中，质子从希夫碱基转移到Asp85，随后质子释放到细胞外介质中，并从细胞质侧再繁殖。结果：在脂质立方相中生长的非孪晶中，bR在基态的结构被解析到1.9埃的分辨率。该结构揭示了八个有序的水分子在假定的质子易位途径的细胞外一半。水分子从希夫碱氮（Lys216）到Glu194和Glu204形成一个连续的氢键网络，包括残基Asp85、Asp212和Arg82，该网络既参与光循环过程中发生的质子移位，也参与稳定基态结构。基质辅助激光解吸/电离质谱（MALDI-MS）分析表明，单晶中存在4种不同的带电荷的脂质。结论：晶体中蛋白质、脂质和水分子的结构在原子分辨率上代表了细菌紫色膜中bR的功能实体。质子从希夫碱转移到细胞外介质是由一个涉及带电残基和水分子的氢键网络介导的。
Background: Bacteriorhodopsin (bR) from Halobacterium salinarum is a proton pump that converts the energy of light into a proton gradient that drives ATP synthesis, The protein comprises seven transmembrane helices and in vivo is organized into purple patches, in which bR and lipids form a crystalline two-dimensional array. Upon absorption of a photon, retinal, which is covalently bound to Lys216 via a Schiff base, is isomerized to a 13-cis,15-anti configuration. This initiates a sequence of events - the photocycle - during which a proton is transferred from the Schiff base to Asp85, followed by proton release into the extracellular medium and reprotonation from the cytoplasmic side.Results: The structure of bR in the ground state was solved to 1.9 Angstrom resolution from non-twinned crystals grown in a lipidic cubic phase. The structure reveals eight well-ordered water molecules in the extracellular half of the putative proton translocation pathway. The water molecules form a continuous hydrogen-bond network from the Schiff-base nitrogen (Lys216) to Glu194 and Glu204 and includes residues Asp85, Asp212 and Arg82, This network is involved both in proton translocation occurring during the photocycle, as well as in stabilizing the structure of the ground state. Nine lipid phytanyl moieties could be modeled into the electron-density maps Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of single crystals demonstrated the presence of four different charged lipid species.Conclusions: The structure of protein, lipid and water molecules in the crystals represents the functional entity of bR in the purple membrane of the bacteria at atomic resolution. Proton translocation from the Schiff base to the extracellular medium is mediated by a hydrogen-bond network that involves charged residues and water molecules.