The dimeric reaction centre light-harvesting 1 (RC-LH1) core complex of Rhodobacter sphaeroides converts absorbed light energy to a charge separation, and then it reduces a quinone electron and proton acceptor to a quinol. The angle between the two monomers imposes a bent configuration on the dimer complex, which exerts a major influence on the curvature of the membrane vesicles, known as chromatophores, where the light-driven photosynthetic reactions take place. To investigate the dimerisation interface between two RC-LH1 monomers, we determined the cryogenic electron microscopy structure of the dimeric complex at 2.9 Å resolution. The structure shows that each monomer consists of a central RC partly enclosed by a 14-subunit LH1 ring held in an open state by PufX and protein-Y polypeptides, thus enabling quinones to enter and leave the complex. Two monomers are brought together through N-terminal interactions between PufX polypeptides on the cytoplasmic side of the complex, augmented by two novel transmembrane polypeptides, designated protein-Z, that bind to the outer faces of the two central LH1 β polypeptides. The precise fit at the dimer interface, enabled by PufX and protein-Z, by C-terminal interactions between opposing LH1 αβ subunits, and by a series of interactions with a bound sulfoquinovosyl diacylglycerol lipid, bring together each monomer creating an S-shaped array of 28 bacteriochlorophylls. The seamless join between the two sets of LH1 bacteriochlorophylls provides a path for excitation energy absorbed by one half of the complex to migrate across the dimer interface to the other half.

中文翻译：

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2.9 Å 球形红细菌二聚体 RC-LH1 核心复合物的冷冻电镜结构：二聚化的结构基础

球形红细菌的二聚反应中心光捕获 1 (RC-LH1) 核心复合物将吸收的光能转化为电荷分离，然后将醌电子和质子受体还原为醌醇。两个单体之间的角度对二聚体复合物施加弯曲构型，这对膜囊泡的曲率产生重大影响，称为色素团，光驱动的光合作用反应发生在那里。为了研究两个 RC-LH1 单体之间的二聚化界面，我们以 2.9 Å 的分辨率确定了二聚体复合物的低温电子显微镜结构。该结构表明，每个单体都由一个中央 RC 组成，该 RC 部分被一个 14 亚基 LH1 环包围，由 PufX 和蛋白质-Y 多肽保持在开放状态，从而使醌能够进入和离开复合物。两个单体通过复合物细胞质侧的 PufX 多肽之间的 N 末端相互作用聚集在一起，并通过两个新的跨膜多肽（称为蛋白-Z）增强，这些多肽与两个中央 LH1 β 多肽的外表面结合。在二聚体界面的精确配合，由 PufX 和蛋白质-Z 实现，通过相对 LH1 αβ 亚基之间的 C 端相互作用，以及通过与结合的磺基奎诺糖基二酰基甘油脂质的一系列相互作用，将每个单体聚集在一起，形成 S 形阵列28 种细菌叶绿素。两组 LH1 细菌叶绿素之间的无缝连接为复合物的一半吸收的激发能量穿过二聚体界面迁移到另一半提供了途径。