Structure of a unique PSII-Pcb tetrameric megacomplex in a chlorophyll <i>d</i> –containing cyanobacterium
Liangliang Shen, Yuanzhu Gao, Kailu Tang, Ruxi Qi, Lutang Fu, Jing‐Hua Chen, Wenda Wang, Xiaomin Ma, Peiyao Li, Min Chen, Tingyun Kuang, Xing Zhang, Jian‐Ren Shen, Peiyi Wang, Guangye Han
Abstract
Acaryochloris marina is a unique cyanobacterium using chlorophyll d (Chl d ) as its major pigment and thus can use far-red light for photosynthesis. Photosystem II (PSII) of A. marina associates with a number of prochlorophyte Chl-binding (Pcb) proteins to act as the light-harvesting system. We report here the cryo-electron microscopic structure of a PSII-Pcb megacomplex from A. marina at a 3.6-angstrom overall resolution and a 3.3-angstrom local resolution. The megacomplex is organized as a tetramer consisting of two PSII core dimers flanked by sixteen symmetrically related Pcb proteins, with a total molecular weight of 1.9 megadaltons. The structure reveals the detailed organization of PSII core consisting of 15 known protein subunits and an unknown subunit, the assembly of 4 Pcb antennas within each PSII monomer, and possible pathways of energy transfer within the megacomplex, providing deep insights into energy transfer and dissipation mechanisms within the PSII-Pcb megacomplex involved in far-red light utilization.