嗜热紫色硫细菌Thermochromatium tepidum光合膜高效光能转换机制研究

Purple sulfur bacterium Thermochromatium tepidum is a thermophile growing in hot spring at 50 C and capable of utilizing the solar spectrum beyond 900 nm. To understand the structure-function relationships of the thermal stability and near-infrared light harvesting, extensive research efforts have been directed to the key photosynthetic membrane proteins, namely, the peripheral light-harvesting complex 2, LH2, and the reaction center (RC) associated core light-harvesting complex 1 (LH1), LH1-RC. Most recently, the crystal structure of Tch. tepidum LH1-RC has been determined with an atomic resolution. On the basis of the knowledge on the key proteins isolated in aqueous phase, the present proposal is intended to unravel, by means of time-resolved spectroscopies, the light-conversion mechanisms of photosynthetic membranes in Tch. tepidum cells and chromatophores. Specifically, the following scientific questions are addressed: (1) Given that a RC is completely encircled by a LH1 in the case of Tch. tepidum, how can electron carriers, ubiquinone (UQ) and ubiquinol (UQH2), interact with LH1 to realize the mutual exchange between inner and outer quinone pool? (2) Ultrafast singlet fission reactions have been reported for longer-conjugated carotenoids in bacterial LHs, the present project is intended to further elucidate the structural and environmental factors regulating its reactivity, and to seek for its biological implications. The results will help to deepen the scientific understandings in the high efficiency of photosynthetic light conversion, and may inspire new development in artificial photosynthesis.

近年来，为了揭示紫色嗜热光合细菌Thermochromatium (Tch.) tepidum的热稳定性和近红外捕光特性的奥秘，人们展开了对其光合膜蛋白—外周捕光天线(LH2)以及内周捕光天线(LH1)与反应中心(RC)构成的核心复合物(LH1-RC)—的结构-功能关系研究，并测定了LH1-RC的原子分辨晶体结构。在前期研究Tch. tepidum分离态膜蛋白的基础上，本项目拟进一步研究载色体(chromatophore) 和菌体光合膜的光能转换机理，探究下述科学问题。(1) RC被LH1的封闭结构所包围，那么RC结合的电子载体醌(UQ, UQH2)是如何进出LH1、从而与膜中的醌库交换的？(2) LHs中类胡萝卜素可通过单重态均裂反应生成两个三重态，调控该反应的分子结构和环境因素是什么？相关研究成果将加深认识光合作用高效光能转换和光保护机理，启发人工模拟光合作用的新思路。

天然光合作用捕光-传能-转能的分子机制可启发高效利用太阳能的新思路。本项目旨在以紫色嗜热菌Thermochromatium (Tch.) tepidum等光合细菌的光合膜蛋白为对象，包括外周捕光天线(LH2)以及内周捕光天线(LH1)与反应中心(RC)构成的核心复合物(LH1-RC)，针对如下两个关键科学问题开展结构-功能关系研究。（i）LH1内结合于RC的醌作为原初电子载体与光合膜中醌库之间交换的动力学机制。(ii) 调控LHs中类胡萝卜素单重态均裂反应的分子结构和环境因素。. 课题研究所取得的重要结果归纳如下。（i）建立了通过类胡萝卜素“电致带移”现象研究醌交换过程的新方法，揭示了LH1-to-RC “上坡式”激发态能量传递等超快过程的动力学机制；（ii）揭示了光合膜蛋白中类胡萝卜素的分子内单重激发态裂分(SF)机制；（iii）发现了紫色光合细菌LHs蛋白的超强一阶非线性极化率；（iv）构建了人工脂膜光合模型及其形貌变化新分析方法。. 该项目已培养研究生9人，包括博士学位毕业生3人，硕士学位毕业生6人。迄今，在包括J. Am. Chem. Soc.，J. Phys. Chem. Lett.，J. Phys. Chem. B，和 Anal. Chem.在内的学术期刊上发表论文16篇。