Structural roles of lipid molecules in the assembly of plant PSII-2LHCII supercomplex

In plants, photosystem Ⅱ (PSⅡ) associates with light-harvesting complexes Ⅱ (LHCⅡ) to form PSⅡ-LHCⅡ supercomplexes. They are multi-subunit supramolecular systems embedded in the thylakoid membrane of chloroplast, functioning as energy-converting and water-splitting machinery powered by light energy. The high-resolution structure of a PSⅡ-LHCⅡ supercomplex, previously solved through cryo-electron microscopy, revealed 34 well-defined lipid molecules per monomer of the homodimeric system. Here we characterize the distribution of lipid-binding sites in plant PSⅡ-LHCⅡ supercomplex and summarize their arrangement pattern within and across the membrane. These lipid molecules have crucial roles in stabilizing the oligomerization interfaces of plant PSⅡ dimer and LHCⅡ trimer. Moreover, they also mediate the interactions among PSⅡ core subunits and contribute to the assembly between peripheral antenna complexes and PSⅡ core. The detailed information of lipid-binding sites within PSⅡ-LHCⅡ supercomplex may serve as a framework for future researches on the functional roles of lipids in plant photosynthesis.