Structure of PSII-LHCII supercomplex: the supramolecular basis for light-harvesting processes in plants

Xuepeng Wei, Xiaodong Su, Peng Cao, Xiuying Liu, Wenrui Chang, Mei Li, Xinzheng Zhang, Zhenfeng Liu
National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China

During oxygenic photosynthesis in plants, the core complex of photosystem II receives excitation energy from the peripheral light-harvesting complexes II (LHCII). The energy transfer pathways between LHCIIs and the core complex of photosystem II (PSII) have been elusive for decades, and the assembly mechanism between these two modules is to be elucidated through high-resolution structural studies on the PSII-LHCII supercomplexes. To this end, the structure of a 1.1-megadalton C2S2-type (C, core complex; S, strongly associated LHCII) PSII–LHCII supercomplex from spinach has been solved at 3.2 Å resolution through single-particle cryoelectron microscopy [1]. The supercomplex is a homodimeric system containing 50 protein subunits, 210 chlorophylls, 56 carotenoids and numerous other cofactors. Each monomer harbors 25 subunits including four large intrinsic core subunits (D1, D2, CP43 and CP47), twelve low-molecular-mass intrinsic subunits, four extrinsic subunits, and five major/minor subunits of LHCIIs. On the luminal side, PsbO, PsbP and PsbQ are three large extrinsic subunits essential for the optimal oxygen-evolving activity of plant PSII. They form a triangular crown shielding the Mn4CaO5-binding domains of CP43 and D1. Within the membrane-embedded region, the major LHCII trimer (majLHCII) and CP26 associate with CP43 on one side, while CP29 binds to CP47 on the other side. The antenna-core interactions are reinforced by three small intrinsic subunits (PsbW, PsbZ and PsbH) binding at their interfaces. Several pairs of closely-connected chlorophylls, potentially mediating the energy-transfer processes between majLHCII/CP29/CP26 and the core complex, have been located.

Figure: Overall structure of spinach PSII-LHCII supercomplex viewed from luminal side.

Reference

[1] Wei, X. P. et al, Nature 2016, 534, 69-74.