能量依赖的淬灭（qE）是植物中一种重要的光保护机制。qE依赖于跨类囊体膜的pH梯度，光系统II（PSII）亚基PsbS及其捕光天线等。PsbS通过感受类囊体腔侧pH降低，发生构象或聚集状态变化，调节捕光蛋白从捕光状态向能量淬灭状态转变，实现光保护功能。本课题组之前解析了菠菜PsbS在酸性pH的晶体结构，但是PsbS感受酸性pH后自身发生何种变化并不清楚；此外由于PsbS与PSII亚基之间的瞬时相互作用，至今未能对PsbS进行定位，与之相互作用的捕光蛋白也未被鉴定出来，所以PsbS如何通过自身变化调节与之相互作用的天线蛋白的功能仍是一个未解的问题。本课题拟以植物PsbS蛋白及PSII超分子复合物为研究对象，解析中性pH条件下PsbS结构以及PSII超分子复合物的结构，对PsbS在PSII中的定位及其相互作用蛋白进行鉴定，从而对PsbS感受pH降低后自身的变化及后续引发qE的机制予以阐释。

Energy-dependent quenching (qE) is an important photoprotective mechanism in plants. qE depends on several key elements, including the transmembrane delta-pH, photosystem II (PSII) subunit PsbS, light-harvesting complexes II (LHCIIs), etc. PsbS first senses the decrease of pH at the thylakoid lumen, then changes its conformation or oligomeric state, and regulates the transition of LHCIIs from light-harvesting state to energy quenching state, so as to achieve the photoprotective function. We have solved the crystal structure of spinach PsbS at acidic pH, but it is still not clear about what kind of changes PsbS experiences after sensing the lumen pH decreasing. In addition, the location of PsbS within PSII and its interacting partners are still unknown due to the transit interaction between PsbS and LHCIIs. So it is still an open question about how the changes of PsbS regulate the LHCIIs to alter their functions. This research project focuses on structural analysis of PsbS and the PSII-LHCII megacomplex. We aim to obtain the structure of PsbS at neutral pH, and to solve the structure of PSII-LHCII megacomplex, thus to localize PsbS and identify its interacting partners within PSII megacomplex. These results will be of great help for understanding the changes of PsbS after sensing the pH decreasing and to elucidate the mechanisms of PsbS-triggered qE function.