Structure and function of a huge photosystem I–fucoxanthin chlorophyll supercomplex from a coccolithophore
Lili Shen, F.M. Ren, Yin-Chu Wang, Zhenhua Li, Mengyuan Zheng, Xiaoyi Li, Wenzheng Fan, Yanyan Yang, Min Sang, Cheng Liu, Guangye Han, Song Qin, Jianhua Fan, Lijin Tian, Tingyun Kuang, Jian‐Ren Shen, Wenda Wang
Abstract
Photosystem I (PSI) is a pigment-protein complex, which converts light energy into chemical energy in photosynthesis. Among photosynthetic organisms, PSI-LHC (light-harvesting complex) structures exhibit substantial differences in their sizes, reflecting adaptation to different light environments. Here we report the structure of a PSI-fucoxanthin chlorophyll a/c binding protein (FCPI) supercomplex from the coccolithophore Emiliania huxleyi (Eh) at 2.79-angstrom resolution by cryo–electron microscopy, which showed a huge Eh-PSI-FCPI supercomplex containing 38 peripheral Eh-FCPI antennae and a linker protein (EhLP) in addition to the PSI core. A network of 819 pigments was found in Eh-PSI-FCPI, which functions to capture and transfer light energy with 95% quantum efficiency. This elucidates how its modular Eh-FCPI arrangement contributes to the expansion of PSI cross section and efficient light harvesting.