PsbP-induced protein conformational changes around Cl− ions in the water oxidizing center of photosystem II
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PsbP is an extrinsic protein of PSII having a function of Ca2+ and Cl− retention in the water-oxidizing center (WOC). In order to understand the mechanism how PsbP regulates the Cl− binding in WOC, we examined the effect of PsbP depletion on the protein structures around the Cl− sites using Fourier transform infrared (FTIR) spectroscopy. Light-induced FTIR difference spectra upon the S1→S2 transition were obtained using Cl−-bound and NO3−-substituted PSII membranes in the presence and absence of PsbP. A clear difference in the amide I band changes by PsbP depletion was observed between Cl−-bound and NO3−-substituted PSII samples, indicating that PsbP binding perturbed the protein conformations around the Cl−ion(s) in WOC. It is suggested that PsbP stabilizes the Cl− binding by regulating the dissociation constant of Cl− and/or an energy barrier of Cl− dissociation through protein conformational changes around the Cl− ion(s).
Additional key wordsMn4CaO5 cluster oxygen evolution photosynthesis
Fourier transform infrared
2-(N-morpholino) ethanesulfonic acid
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