title: Probing the topography of the photosystem II oxygen evolving complex: PsbO is required for efficient calcium protection of the manganese cluster against dark-inhibition by an artificial reductant.
abstract: The photosystem II (PSII) manganese-stabilizing protein (PsbO) is known to be the essential PSII extrinsic subunit for stabilization and retention of the Mn and Cl(-) cofactors in the oxygen evolving complex (OEC) of PSII, but its function relative to Ca(2+) is less clear. To obtain a better insight into the relationship, if any, between PsbO and Ca(2+) binding in the OEC, samples with altered PsbO-PSII binding properties were probed for their potential to promote the ability of Ca(2+) to protect the Mn cluster against dark-inhibition by an exogenous artificial reductant, N,N-dimethylhydroxylamine. In the absence of the PsbP and PsbQ extrinsic subunits, Ca(2+) and its surrogates (Sr(2+), Cd(2+)) shield Mn atoms from inhibitory reduction (Kuntzleman et al., Phys Chem Chem Phys 6:4897, 2004). The results presented here show that PsbO exhibits a positive effect on Ca(2+) binding in the OEC by facilitating the ability of the metal to prevent inhibition of activity by the reductant. The data presented here suggest that PsbO may have a role in the formation of the OEC-associated Ca(2+) binding site by promoting the equilibrium between bound and free Ca(2+) that favors the bound metal.
authors: Department of Molecular, Cellular, and Developmental Biology, The University of Michigan, Ann Arbor, MI 48109-1048, USA. popelka@umich.edu
authors: Hana
authors: H
authors: Popelkova
authors: Nicholas
authors: N
authors: Boswell
authors: Charles
authors: C
authors: Yocum
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D003624:Darkness; D004123:Dimethylamines / Q000494:pharmacology; D004492:Edetic Acid / Q000378:metabolism; D004795:Enzyme Stability; D008345:Manganese / Q000378:metabolism; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D004123:Dimethylamines; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011994:Recombinant Proteins; C054266:photosystem II manganese-stabilizing protein; D008345:Manganese; C063231:N,N-dimethylhydroxylamine; D004492:Edetic Acid; D010100:Oxygen; D002118:Calcium