At the origin of the selectivity of the chlorophyll-binding sites in Light Harvesting Complex II (LHCII)

The photosynthetic light-harvesting complexes (LHCs) are responsible for light absorption due to their pigmentbinding properties. These pigments are primarily Chlorophyll (Chl) molecules of type a and b, which ensure an excellent coverage of the visible light spectrum. To date, it is unclear which factors drive the selective binding of different Chl types in the LHC binding pockets. To gain insights into this, we employed molecular dynamics simulations on LHCII binding different Chl types. From the resulting trajectories, we have calculated the binding affinities per each Chl-binding pocket using the Molecular mechanics Poisson-Boltzmann surface area (MMPBSA) model. To further examine the importance of the nature of the axial ligand in tuning the Chl selectivity of the binding sites, we used Density Functional Theory (DFT) calculations. The results indicate that some binding pockets have a clear Chl selectivity, and the factors governing these selectivities are identified. Other binding pockets are promiscuous, which is consistent with previous in vitro reconstitution studies. DFT calculations show that the nature of the axial ligand is not a major factor in determining the Chl binding pocket selectivity, which is instead probably controlled by the folding process.

Automated summary

The light-harvesting complexes (LHCs) in photosynthesis absorb light through the binding properties of their pigments, mainly Chlorophyll (Chl) molecules of type a and b. The factors determining the selective binding of different Chl types in LHC binding pockets are still unclear. Molecular dynamics simulations and Density Functional Theory (DFT) calculations were used to investigate the Chl selectivity and the influence of the axial ligand in the binding sites. The results suggest that some binding pockets show clear Chl selectivity, while others are promiscuous, and the folding process likely plays a role in determining the selectivity.