光合玫瑰菌核心光合复合体的结构与功能研究

Roseiflexus castenholzii is a new type thermophilic filamentous anoxygenic photosynthetic bacterium, it acquired a unique and high efficient light harvesting and electron transport system during evolution. Different from higher plants and other photosynthetic bacteria, it doesn’t contain the antenna complexes, the only light harvesting complex (LH) is assembled by several LHαβ subunits to form a ring like structure, having the L, M and cytochrome c subunits composed reaction center (RC) tightly bound in middle. Especially, a novel electron carrier protein complex ACIII replaced the cytochrome bc1/b6f complex in the canonical electron transport chain of photosynthesis and respiration. It transfers electron from the reaction center to a new blue copper protein auracyanin, drives formation of the transmembrane proton gradient, providing energy for bacterial growth. However, this novel photosynthetic system has only been globally investigated in a preliminary way. Our group have obtained the LH-RC and ACIII complex samples with high purity and efficiency recently. Based on this achievement, this proposal will aim to determine the three dimensional structures of LH-RC and ACIII complex at atomic resolution, through combination of X-ray crystallography and Cryo-electron microscopy technique, and illustrate the molecular mechanisms of light harvesting, electron transfer and energy transformation by accompanied functional studies, contributing theory evidence for development of new resources of energy.

光合玫瑰菌Roseiflexus castenholzii是一种新型的嗜热丝状不产氧光合细菌，在进化中获得了一套独特高效的光能吸收和电子传递系统。区别于高等植物和其他光合细菌，这一系统没有外周天线，唯一的捕光复合体（LH）由多个LHαβ亚基组成环状，紧密包围着L、M和细胞色素c亚基组成的反应中心（RC）。更特别的是，一种全新的电子载体蛋白复合体ACIII取代了传统光合和呼吸电子传递链中的细胞色素bc1/b6f复合物，将电子从反应中心传递到一个新的蓝铜蛋白金色蓝素，推动质子跨膜梯度的形成，为细菌生长提供能量。然而国内外对这一独特光合系统的研究仍处于起步阶段。申请人前期已获得高纯度、高活性的LH-RC和ACIII复合体样品，本项目将在此基础上综合运用X-射线晶体学和冷冻电镜技术，解析这两个复合体原子分辨率的三维结构，结合功能实验阐明其吸收、传递和转化光能的分子机制，为新能源的开发提供理论依据。

光合玫瑰菌是一种新型的嗜热丝状不产氧光合细菌，在进化中获得了一套简洁高效的光能吸收、转化和循环电子传递系统。此系统没有外周天线，唯一的捕光复合体（LH）由多个LHαβ亚基组成环状，紧密包围着L、M和细胞色素c亚基组成的反应中心（RC）。特别的是，一种全新的电子载体蛋白复合体ACIII取代了光合和呼吸电子传递链都不可或缺的细胞色素bc1/b6f复合物，氧化氢醌并将电子传递给一个新的蓝铜蛋白金色蓝素（Au），推动质子跨膜动力势的产生和ATP的合成，为细菌生长提供能量。然而国内外对此独特光合系统的研究仍处于起步阶段。本项目结合冷冻电镜和X-射线晶体学方法，解析了RC-LH复合体4.1Å和3.3Å分辨率的电镜结构，揭示了其吸收和传递光能的超分子基础；解析了ACIII复合体氧化态3.3Å和还原态3.5Å分辨率的电镜结构，揭示了其氧化氢醌、传递电子和跨膜转运质子的结构基础，提出了一种新的氧化还原作用偶联的质子转运机制；解析了下游电子受体Au氧化态2.2Å和还原态2.0Å分辨率的晶体结构，明确了其在循环电子传递中的作用方式。我们对此循环电子传递链的结构和功能研究，揭示了一种新的电子传递和能量转化机制，丰富了电子传递和质子泵作用机制的多样性和协同进化，为进一步系统研究光合细菌吸收、传递和转化光能的机理奠定了坚实的基础。