Mechanistic insights into the function of the ancient light-harvesting protein LHCSR3 in light energy dissipation in Chlamydomonas reinhardtii

莱茵衣藻（Chlamydomonas reinhardtii）的qE能力受环境条件的影响，并受强光诱导。qE容量随着LHCSR3蛋白的光依赖性增加而成比例地增加。LHCSR3的缺失或耗尽会消除细胞耗散有害多余能量的能力，这表明LHCSR3是高效qE所必需的（Peers等，2009）。LHCSR3在功能上与PSII-LHCII超配合物相互作用（Tokutsu & Minagawa, 2013），并且需要PSBR才能有效结合PSII-LHCII （Xue et al, 2015）。尽管对LHCSR3功能的理解取得了重大进展，但主要问题仍未解决，例如：(i) LHCSR3蛋白磷酸化的功能后果是什么（ii）为什么LHCSR3与PSI和较大的PSI- fnr和/或假定的CEF超复合物结合，LHCSR3在保护PSI方面起作用吗（iii） PSI超复合物中的蛋白质-蛋白质相互作用伙伴是什么，以及（iv） LHCSR3与其他LHC多肽和光合蛋白复合物PSII和PSI的化学计量学是什么。为了研究LHCSR3在C. reinhardtii中功能的机制相关问题，我们设计了结合反向遗传学、磷酸化蛋白质组学和定量蛋白质组学以及生理测量和时间分辨光学吸收光谱的实验策略。

The qE capacity of Chlamydomonas reinhardtii is dependent on environmental conditions and is inducible by growth in high light. The qE capacity increases proportionally with the light-dependent increase of the LHCSR3 protein. Deletion or depletion of LHCSR3 abolishes the ability of the cells to dissipate harmful excess energy, demonstrating that LHCSR3 is required for efficient qE (Peers et al, 2009). LHCSR3 functionally interacts with PSII-LHCII supercomplexes (Tokutsu & Minagawa, 2013) and requires PSBR for efficient binding to PSII-LHCII (Xue et al, 2015). Despite the significant progress in the understanding of LHCSR3 function, major questions remain unsolved such as: (i) what are the functional consequences of LHCSR3 protein phosphorylation (ii) why does LHCSR3 bind to PSI and larger PSI-FNR and/or putative CEF supercomplexes, does LHCSR3 function in protecting PSI (iii) what are the protein-protein-interaction partner(s) in PSI supercomplexes, and (iv) what is the stoichiometry of LHCSR3 with other LHC polypeptides and the photosynthetic protein complexes PSII and PSI. To investigate these mechanistically related problems concerning LHCSR3 function in C. reinhardtii we designed experimental strategies combining reverse genetics, phosphoproteomics and quantitative proteomics with physiological measurements and time resolved optical absorption spectroscopy.