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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >BACTERIORHODOPSIN - THE EFFECT OF BILAYER THICKNESS ON 2D-ARRAY FORMATION, AND THE STRUCTURAL RE-ALIGNMENT OF RETINAL THROUGH THE PHOTOCYCLE
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BACTERIORHODOPSIN - THE EFFECT OF BILAYER THICKNESS ON 2D-ARRAY FORMATION, AND THE STRUCTURAL RE-ALIGNMENT OF RETINAL THROUGH THE PHOTOCYCLE

机译：细菌视紫红质-双层厚度对二维阵列形成的影响以及通过细菌的视网膜结构重排

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From our earlier extensive protein-lipid reconstitution studies, the conditions under which bacteriorhodopsin forms organised 2D arrays in large unilamellar vesicles have been established using freeze-fracture electron microscopy. In a background bilayer matrix of phosphatidylcholine (diC(14:0)), the protein can form arrays only when the anionic purple membrane lipid, phosphatidylglycerol phosphate (or the sulphate derivative) is present. Here we have now extended this work to investigate the effect of bilayer thickness on array formation. Phosphatidylcholines with various chain lengths (diC(12:0), diC(14:0) and diC(16:0)) and which form bilayers of well defined bilayer thickness, have been used as the matrix into which bacteriorhodopsin, together with minimal levels (c. 4-10 lipids per bacteriorhodopsin) of diphytanyl phosphatidylglycerol phosphate, has been reconstituted. Arrays are formed in all complexes and bilayer thickness appears only to alter the type of array formed, either as an orthogonal or as an hexagonal array. Secondly, we have previously deduced the entire conformation of retinal within the bacteriorhodopsin binding pocket in oriented purple membrane fragments. Using solid state deuterium NMR of the specifically deutero-methylated retinal labelled at each of the methyl positions in the molecule, the C-CD3 bond vectors of the chromophore have been resolved to +/-2 degrees. The ring conformation is 6-S-trans, but the polyene chain is slightly curved when in the protein binding site. Here, we describe studies on the protein in both the ground state and the trapped M(412)-state of the photocycle, to show that the orientation of the central methyl group (C-19) on the polyene chain, which is at 40 degrees+/-1 degrees with respect to the membrane normal, only changes its orientation by approximately 4 degrees upon 13-cis-isomerization. Thus, it is the Schiff base end of the chromophore which moves upon light incidence acting as a local switch on the protein in the photocycle, whilst the ring end of the chromophore moves rather less. [References: 20]
机译：根据我们较早的广泛的蛋白质-脂质重构研究，使用冷冻断裂电子显微镜已经确定了细菌视紫红质在大单层囊泡中形成二维阵列的条件。在磷脂酰胆碱（diC（14：0））的背景双层基质中，只有当存在阴离子紫色膜脂质，磷脂酰甘油磷酸酯（或硫酸盐衍生物）时，蛋白质才能形成阵列。在这里，我们现在将这项工作扩展到研究双层厚度对阵列形成的影响。具有各种链长（diC（12：0），diC（14：0）和diC（16：0））且形成双层厚度明确的双层的磷脂酰胆碱已用作基质，其中细菌视紫红质和最小的已重新构建了双植烷酰基磷脂酰甘油磷酸的水平（每细菌视紫红质约4-10个脂质）。阵列以所有复合物的形式形成，双层厚度似乎只是改变形成的阵列的类型，呈正交或六边形阵列。其次，我们先前已经推导了定向紫膜片段中细菌视紫红质结合袋内的整个视网膜构象。使用在分子中每个甲基位置标记的特定氘代甲基化视网膜的固态氘核NMR，发色团的C-CD3键载体已解析为+/- 2度。环构象是6-S-反式，但在蛋白质结合位点时，多烯链略微弯曲。在这里，我们描述了对蛋白质在光周期的基态和捕获的M（412）状态的研究，以表明多烯链上中心甲基（C-19）的方向为40相对于膜法线的1度+/- 1度，仅在13-顺式异构化时将其取向改变约4度。因此，正是发色团的席夫基端在光入射时移动，作为光循环中蛋白质上的局部开关，而发色团的环端移动得少。 [参考：20]

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