Structural and functional modulation of the manganese cluster in Ca(2+)-depleted photosystem II induced by binding of the 24-kilodalton extrinsic protein.
Depletion of functional Ca2+ from photosystem (PS) II membranes impairs O2 evolution. Redox properties of the Mn cluster as probed by thermoluminescence were modified differently in Ca(2+)-depleted PSII depending on the procedure for Ca2+ extraction. Ca2+ depletion by low-pH treatment gave rise to an abnormally modified S2 state exhibiting a thermoluminescence band with elevated peak temperature accompanied by a marked upshift in threshold temperature for its formation, whereas Ca2+ depletion by NaCl washing in the light followed by the addition of EDTA could generate a similarly modified S2 state only when the Ca(2+)-depleted PSII was reconstituted with the 24-kDa extrinsic proteins. These results indicated that manifestation of the abnormal properties of the Ca(2+)-depleted S2 state is significantly contributed by the association of the 24-kDa extrinsic protein to PSII. It was inferred that the 24-kDa extrinsic protein regulates the structure and function of the Mn cluster in the absence of functional Ca2+ through a conformational modulation of the intrinsic protein(s) that bind(s) both Mn and Ca. Features of the extrinsic protein-dependent modulation of the Mn cluster were discussed in relation to the function of Ca2+ in O2 evolution.
Ono
T
T
Solar Energy Research Group, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
Izawa
S
S
Inoue
Y
Y
D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003624:Darkness; D007700:Kinetics; D008027:Light; D008163:Luminescent Measurements; D008345:Manganese / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants / Q000378:metabolism; D011485:Protein Binding; D013816:Thermodynamics
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D008345:Manganese; D010100:Oxygen; D002118:Calcium