Tani Kazutoshi, Kanno Ryo, Ji Xuan-Cheng, Hall Malgorzata, Yu Long-Jiang, Kimura Yukihiro, Madigan Michael T, Mizoguchi Akira, Humbel Bruno M, Wang-Otomo Zheng-Yu
Graduate School of Medicine, Mie University, Tsu, Mie 514-8507, Japan.
Imaging Section, Research Support Division, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1, Tancha, Onna-son, Kunigami-gun, Okinawa 904-0495, Japan.
Biochemistry. 2021 Jul 29. doi: 10.1021/acs.biochem.1c00360.
() is one of the most widely used model organisms in bacterial photosynthesis. This purple phototroph is characterized by the presence of both rhodoquinone (RQ) and ubiquinone as electron carriers and bacteriochlorophyll (BChl) esterified at the propionic acid side chain by geranylgeraniol (BChl ) instead of phytol. Despite intensive efforts, the structure of the light-harvesting-reaction center (LH1-RC) core complex from remains at low resolutions. Using cryo-EM, here we present a robust new view of the LH1-RC at 2.76 Å resolution. The LH1 complex forms a closed, slightly elliptical ring structure with 16 αβ-polypeptides surrounding the RC. Our biochemical analysis detected RQ molecules in the purified LH1-RC, and the cryo-EM density map specifically positions RQ at the Q site in the RC. The geranylgeraniol side chains of BChl coordinated by LH1 β-polypeptides exhibit a highly homologous tail-up conformation that allows for interactions with the bacteriochlorin rings of nearby LH1 α-associated BChls . The structure also revealed key protein-protein interactions in both N- and C-terminal regions of the LH1 αβ-polypeptides, mainly within a face-to-face structural subunit. Our high-resolution LH1-RC structure provides new insight for evaluating past experimental and computational results obtained with this old organism over many decades and lays the foundation for more detailed exploration of light-energy conversion, quinone transport, and structure-function relationships in this pigment-protein complex.
（）是细菌光合作用中使用最广泛的模式生物之一。这种紫色光合生物的特征是存在作为电子载体的视黄醌（RQ）和泛醌，以及在丙酸侧链上由香叶基香叶醇酯化的细菌叶绿素（BChl）（BChl ）而不是叶绿醇。尽管付出了巨大努力，但来自的光捕获反应中心（LH1-RC）核心复合物的结构仍处于低分辨率状态。利用冷冻电镜，我们在此展示了分辨率为2.76 Å的LH1-RC的全新可靠视图。LH1复合物形成一个封闭的、略呈椭圆形的环结构，由16个αβ多肽围绕着反应中心。我们的生化分析在纯化的LH1-RC中检测到了RQ分子，并且冷冻电镜密度图明确将RQ定位在反应中心的Q位点。由LH1 β多肽配位的BChl 的香叶基香叶醇侧链呈现出高度同源的尾向上构象，这使得它们能够与附近LH1 α相关BChls 的细菌叶绿素环相互作用。该结构还揭示了LH1 αβ多肽的N端和C端区域中的关键蛋白质-蛋白质相互作用，主要是在一个面对面的结构亚基内。我们的高分辨率LH1-RC结构为评估过去几十年来用这种古老生物获得的实验和计算结果提供了新的见解，并为更详细地探索这种色素-蛋白质复合物中的光能转换、醌转运和结构-功能关系奠定了基础。
