Functional roles of the amino- and carboxyl-regions of PsbP protein in photosystem II

Abstract

The PsbP protein of photosystem II (PSII) regulates the binding properties of Ca2+ and Cl−, indispensable cofactors for water-splitting reaction, and stabilizes the Mn cluster. It was reported that amino (N)-terminal sequence of PsbP is important for the ion retention in PSII [Ifuku et al., Photosynth. Res. 2005, 84: 251-255], while molecular function of the carboxyl (C)-terminal domain of PsbP has not been characterized. In this study, we investigated function of the C-terminal domain of PsbP by site-directed mutagenesis based on the crystal structure. Among the mutated PsbP investigated, PsbP-H144A with the substitution of conserved His144 to Ala showed significantly lower ability to recover the activity of NaCl-treated PSII membranes, whereas PsbP-H144A could bind to PSII in a manner similar to wild-type protein. This His144 residue coordinates Zn2+ in the crystal structure of spinach PsbP (PDB ID: 2VU4), while exact functional role of His144 in PSII remains to be elucidated. Our results suggest that both of the amino- and the carboxyl-terminal regions of PsbP are important for ion-retention within PSII.