蓝藻碳酸氢根转运蛋白的结构与调控机理研究

蓝藻在响应大气二氧化碳浓度的变化过程中进化出一种二氧化碳浓缩机制（CCM），可以主动转运无机碳到细胞内，以确保RuBisCO周围较高的二氧化碳浓度，从而显著提高光合固碳效率。蓝藻的无机碳摄取系统包含五种不同的碳酸氢根转运系统，并被视为增强C3植物光合作用的理想靶标，但其中两种转运蛋白的分子结构、转运机制及调控机理尚不清楚。本项目将深入研究蓝藻碳酸氢根转运蛋白SbtA与BCT1的转运活性与调控机理，解析SbtA-SbtB与BCT1复合体的蛋白结构并对其组装机理、转运活性以及关键氨基酸位点的功能活性进行深入分析，对植物与光合细菌的碳酸氢根转运蛋白同源物进行比较，揭示碳酸氢根转运在固碳过程中的关键作用，为植物光合作用的改造与应用提供研究基础。

The single-cell cyanobacteria are among the most abundant organisms on earth. They created and help to sustain our atmosphere, and account for an estimated 20-30% of current global carbon fixation. Cyanobacteria have evolved a unique CO2 concentrating mechanism (CCM) to increase the intracellular concentration of CO2 feeding to RuBisCO encapsulated in carboxysomes to improve photosynthesis. CCM contains three bicarbonate transporters transporting dissolved inorganic carbon (Ci), HCO3-, across the membrane to satisfy the great need of CO2 of RuBisCO. Among them, SbtA and BicA are sodium-dependent HCO3- transporters possessing high affinity and constitutive medium affinity, respectively; BCT1 is a HCO3- transporter complex powered by ATP hydrolysis. These Ci uptake systems have been considered as ideal targets to enhance photosynthesis in C3 plants. However, the molecular mechanisms of transport and activity regulation of Ci transporters remain largely unknown, which to a large extent limits their application in photosynthesis improvement..This project focuses on the structural and mechanistic study of the cyanobacterial bicarbonate transporters SbtA and BCT1. The aims of this project are to determine the complex structure of SbtA-SbtB and CmpABCD and to characterize the assembly and transport mechanism, by comprehensive application of single-particle cryo-EM and crystallography. The transport and regulatory mechanism revealed by this project will provide a valuable case to investigate allosteric regulation of membrane transporters. More importantly, there has been increasing interests in using CCM and Ci uptake systems to improve photosynthesis efficiency in plants and crops.