The primary light reaction of photosynthesis in plants happens at
photosystem II (PSII), a membrane-embedded supramolecular machine that
catalyzes the water-splitting reaction. Surrounding the PSII is a number of
peripheral antenna complexes that dynamically associate with it to form the
PSII-LHCII supercomplexes of variable sizes in response to different light
conditions.

Isolated from Arabidopsis and peas, the C2S2M2-type supercomplex is the
largest stable form of PSII-LHCII supercomplex, and crucial for plants to
achieve optimal light-harvesting efficiency when they are under low-light
conditions. Structural analysis of the C2S2M2 supercomplex is an important
step to understanding the molecular mechanisms that plants use in light
harvesting, light energy transfer, and PSII functional regulation.

A team of researchers from the Institute of Biophysics (IBP) at the Chinese
Academy of Sciences (CAS) used cryo-electron microscopy (cryo-EM) to resolve
structures of C2S2M2-type PSII-LHCII supercomplex from peas at 2.7 and 3.2?
resolution, respectively. The study revealed the overall structural features
and the arrangement of each individual subunit, as well as the sophisticated
pigment network and the complete energy transfer pathways within the
supercomplex. The comparison of two C2S2M2 structures suggests the potential
mechanism of functional regulation on the light-harvesting process and the
oxygen-evolving activity of plant PSII.

[science.sciencemag.org]