Primary Citation of Related Structures:   8XR6
PubMed Abstract: 
Cryptophytes are ancestral photosynthetic organisms evolved from red algae through secondary endosymbiosis. They have developed alloxanthin-chlorophyll a/c2-binding proteins (ACPs) as light-harvesting complexes (LHCs). The distinctive properties of cryptophytes contribute to efficient oxygenic photosynthesis and underscore the evolutionary relationships of red-lineage plastids. Here we present the cryo-electron microscopy structure of the Photosystem II (PSII)-ACPII supercomplex from the cryptophyte Chroomonas placoidea. The structure includes a PSII dimer and twelve ACPII monomers forming four linear trimers. These trimers structurally resemble red algae LHCs and cryptophyte ACPI trimers that associate with Photosystem I (PSI), suggesting their close evolutionary links. We also determine a Chl a-binding subunit, Psb-γ, essential for stabilizing PSII-ACPII association. Furthermore, computational calculation provides insights into the excitation energy transfer pathways. Our study lays a solid structural foundation for understanding the light-energy capture and transfer in cryptophyte PSII-ACPII, evolutionary variations in PSII-LHCII, and the origin of red-lineage LHCIIs.
Organizational Affiliation: 
Marine Biotechnology Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China. zhangyz@sdu.edu.cn.
MOE Key Laboratory of Evolution and Marine Biodiversity, Frontiers Science Center for Deep Ocean Multispheres and Earth System & College of Marine Life Sciences, Ocean University of China, Qingdao, China. zhangyz@sdu.edu.cn.
Laboratory for Marine Biology and Biotechnology, Qingdao Marine Science and Technology Center, Qingdao, China. zhangyz@sdu.edu.cn.
MOE Key Laboratory of Evolution and Marine Biodiversity, Frontiers Science Center for Deep Ocean Multispheres and Earth System & College of Marine Life Sciences, Ocean University of China, Qingdao, China.
Laboratory for Marine Biology and Biotechnology, Qingdao Marine Science and Technology Center, Qingdao, China.
Marine Biotechnology Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China.
Hubei Key Laboratory of Agricultural Bioinformatics, College of Informatics, Huazhong Agricultural University, Wuhan, China.
Hubei Key Laboratory of Agricultural Bioinformatics, College of Informatics, Huazhong Agricultural University, Wuhan, China. gaojun@mail.hzau.edu.cn.
MOE Key Laboratory of Evolution and Marine Biodiversity, Frontiers Science Center for Deep Ocean Multispheres and Earth System & College of Marine Life Sciences, Ocean University of China, Qingdao, China. luning.liu@liverpool.ac.uk.
Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK. luning.liu@liverpool.ac.uk.
Marine Biotechnology Research Center, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China. zhaols@sdu.edu.cn.
Laboratory for Marine Biology and Biotechnology, Qingdao Marine Science and Technology Center, Qingdao, China. zhaols@sdu.edu.cn.
(1~{R})-3,5,5-trimethyl-4-[(3~{E},5~{E},7~{E},9~{E},11~{E},13~{E},15~{E},17~{E})-3,7,12,16-tetramethyl-18-(2,6,6-trimethylcyclohexen-1-yl)octadeca-3,5,7,9,11,13,15,17-octaen-1-ynyl]cyclohex-3-en-1-ol C40 H54 O UNJKJDIRJWIHLL-BQLQDKTLSA-N