Structural Insights into Substrate Selectivity, Catalytic Mechanism, and Redox Regulation of Rice Photosystem Ⅱ Core Phosphatase

摘要

Photosystem Ⅱ (PSⅡ) core phosphatase (PBCP) selectively dephosphorylates PSll core proteins including D1,D2,CP43,and PsbH.PBCP function is required for efficient degradation of the D1 protein in the repair cycle of PSⅡ,a supramolecular machinery highly susceptible to photodamage during oxygenic photosyn thesis.Here we present structural and functional studies of PBCP from Oryza sativa (OsPBCP).In a symmetrical homodimer of OsPBCP,each monomer contains a PP2C-type phosphatase core domain,a large motif characteristic of PBCPs,and two small motifs around the active site.The large motif contributes to the formation of a substrate-binding surface groove,and is crucial for the selectivity of PBCP toward PSⅡ core proteins and against the light-harvesting proteins.Remarkably,the phosphatase activity of OsPBCP is strongly inhibited by glutathione and H2O2.S-Glutathionylation of cysteine residues may introduce steric hindrance and allosteric effects to the active site.Collectively,these results provide detailed mechanistic insights into the substrate selectivity,redox regulation,and catalytic mechanism of PBCP.