pH-Responsive Binding Properties of Light-Harvesting Complexes in a Photosystem II Supercomplex Investigated by Thermodynamic Dissociation Kinetics Analysis

Reorganization of photosynthetic proteins on the thylakoid membrane is an important regulatory process for photoacclimation in photosynthetic organisms. However, the underlying mechanism has been poorly understood due to the lack of methods to analyze the interactions between membrane proteins. To investigate the mechanism, we demonstrated the binding properties of light-harvesting complex proteins (LHCs) in a photosystem II (PSII) supercomplex regulated by pH conditions, which primarily responded to environmental light conditions, using a thermodynamic dissociation kinetics analysis. The results showed that the strongly bound LHCs (similar to 60%) were responsive to pH conditions, whereas the moderately and loosely bound LHCs (similar to 40%) were nonresponsive. This result implies that the pH condition alters the binding properties of LHCs in the PSII supercomplex, inducing the reorganization of protein complexes.