Abstract
The extrinsic proteins of photosytem II (PSII), PsbO, PsbP and PsbQ, are known to stabilize the oxygen-evolving center (OEC) and regulate the Ca2+ and Cl- requirement. However, the mechanism underlying such functions has yet to be clarified. We investigated the involvement of the extrinsic proteins in the OEC reactions using FTIR spectroscopy. Upon PsbP and PsbQ deletion, clear changes were observed in the amide I bands of the S2/S1 FTIR difference spectrum, whereas further PsbO deletion did not change the spectrum. Normal amide I bands recovered by recombination of PsbP, although the recovery was not observed by Δ15PsbP that lacks 15 N-terminal residues. Recombination of 13C-labeled PsbP showed the same changes as unlabeled PsbP. These results indicate that the N-terminal residues of PsbP directly interact with OEC and affect its protein conformation. It is suggested that this direct interaction of PsbP induces its function of Ca2+/Cl- retention.
