The crystal structure of the light-harvesting complex II (B800-850) from Rhodospirillum molischianum
The crystal structure of the light-harvesting complex II (B800-850) from Rhodospirillum molischianum
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DOI：
10.1016/s0969-2126(96)00063-9
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发表时间：
1996-05-15
期刊：
影响因子：
5.7
通讯作者：
Michel, H
中科院分区：
文献类型：
--
作者：
Koepke, J;Hu, XC;Michel, H
背景：光捕获复合物 II (LH-2s) 是一种完整的膜蛋白，在紫色细菌的光合膜中形成环状结构，即 αβ-异二聚体的寡聚物。它们含有大量经过优化组织的发色团，用于光吸收和快速光能迁移。最近，嗜酸红假单胞菌九聚体LH-2的结构已被确定。我们在这里报告了来自莫利斯基红螺菌的八聚体 LH-2 的晶体结构。这些蛋白质结构的相似性和差异性的揭示可能为细菌光合作用的有效能量转移机制提供有价值的见解。结果：使用X射线衍射在2.4埃分辨率下通过分子置换确定了来自Rs, molischianum的LH-2的晶体结构，该晶体结构显示出两个由16个跨膜螺旋亚基组成的同心圆柱体，包含两个细菌叶绿素-a (BChl-a)分子环。一个环包括十六个垂直于膜平面的B850 BChl-as和另外八个几乎平行于膜平面的B800 BChl-as；八种跨膜番茄红素（该复合物中的主要类胡萝卜素）在 B800 和 B850 BChl-as 之间伸展。 B800 BChl-as 表现出与 Rps 不同的连接。嗜酸菌（天冬氨酸是镁配体，与嗜酸菌中的甲酰甲硫氨酸相反）。结论：来自不同细菌的光捕获复合物呈现不同的环尺寸。在LH-2卢比中。 molischianum 中，相邻 B850 和 B800 BChl-as 的 Q(y) 跃迁偶极矩几乎彼此平行，也就是说，它们针对福斯特激子转移进行了最佳排列。这些叶绿素之间的 Dexter 能量转移也可以通过番茄红素和 B850 BChl-a 植基尾介导的相互作用实现。与每个异二聚体单元相关的B800 BChl-a和两个B850 BChl-as之一与番茄红素处于范德华距离内，使得番茄红素和BChl-as之间的单线态和三线态能量转移可以通过Dexter机制发生。 B850 BChl-as 的环形结构对于光能传输来说是最佳的，因为它对所有空间吸收和发射特性进行采样，并将所有振荡器强度置于能量较低、热可接近的激子态。
Background: The light-harvesting complexes II (LH-2s) are integral membrane proteins that form ring-like structures, oligomers of alpha beta-heterodimers, in the photosynthetic membranes of purple bacteria. They contain a large number of chromophores organized optimally for light absorption and rapid light energy migration. Recently, the structure of the nonameric LH-2 of Rhodopseudomonas acidophila has been determined; we report here the crystal structure of the octameric LH-2 from Rhodospirillum molischianum. The unveiling of similarities and differences in the architecture of these proteins may provide valuable insight into the efficient energy transfer mechanisms of bacterial photosynthesis.Results: The crystal structure of LH-2 from Rs, molischianum has been determined by molecular replacement at 2.4 Angstrom resolution using X-ray diffraction, The crystal structure displays two concentric cylinders of sixteen membrane-spanning helical subunits, containing two rings of bacteriochlorophyll-a (BChl-a) molecules. One ring comprises sixteen B850 BChl-as perpendicular to the membrane plane and the other eight B800 BChl-as that are nearly parallel to the membrane plane; eight membrane-spanning lycopenes (the major carotenoid in this complex) stretch out between the B800 and B850 BChl-as. The B800 BChl-as exhibit a different ligation from that of Rps. acidophila (aspartate is the Mg ligand as opposed to formyl-methionine in Rps. acidophila).Conclusions: The light-harvesting complexes from different bacteria assume various ring sizes. In LH-2 of Rs. molischianum, the Q(y) transition dipole moments of neighboring B850 and B800 BChl-as are nearly parallel to each other, that is, they are optimally aligned for Forster exciton transfer. Dexter energy transfer between these chlorophylls is also possible through interactions mediated by lycopenes and B850 BChl-a phytyl tails; the B800 BChl-a and one of the two B850 BChl-as associated with each heterodimeric unit are in van der Waals distance to a lycopene, such that singlet and triplet energy transfer between lycopene and the BChl-as can occur by the Dexter mechanism. The ring structure of the B850 BChl-as is optimal for light energy transfer in that it samples all spatial absorption and emission characteristics and places all oscillator strength into energetically low lying, thermally accessible exciton states.