Effects of extrinsic proteins on the protein conformation of the oxygen-evolving center in cyanobacterial photosystem II as revealed by Fourier transform infrared spectroscopy
Abstract
Extrinsic proteins of photosystem II (PSII) play an important role in optimizing oxygen-evolving reactions in all oxyphototrophs. The currently available crystal structures of cyanobacterial PSII core complexes show the binding structures of the extrinsic proteins, PsbO, PsbV, and PsbU; however, how the individual extrinsic proteins affect the structure and the function of the oxygen-evolving center (OEC) in cyanobacterial PSII remains unknown. In this study, we have investigated the effects of the binding of the extrinsic proteins on the protein conformation of the OEC in PSII core complexes from the thermophilic cyanobacterium Thermosynechococcus elongatus, using light-induced Fourier transform infrared (FTIR) difference spectroscopy. Upon removal of the three extrinsic proteins, an S₂-minus-S₁ FTIR difference spectrum measured in the presence of a high CaCl₂ concentration showed a drastic change in amide I bands, reflecting perturbation of the secondary structures of polypeptides, whereas the overall spectral intensity was lost at a low CaCl₂ concentration, indicative of inactivation of the Mn₄CaO₅ cluster. The amide I features as well as the overall intensity were recovered mainly by binding of PsbO, while complete amide I ...Continue Reading
References
The PsbQ protein defines cyanobacterial Photosystem II complexes with highest activity and stability
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