title: Structural dynamics of the manganese-stabilizing protein-effect of pH, calcium, and manganese.
abstract: The photosystem-II-associated 33-kDa extrinsic manganese-stabilizing protein is found in all oxygen-evolving organisms. In this paper, we show that this protein undergoes pH-induced conformational changes in the physiological pH range. At a neutral pH of 7.2, the hydrophobic amino acid residues that are most likely located inside the beta barrel are "closed" and the protein binds neither Mn2+ nor Ca2+ ions. When the protein is transferred to a solution with a slightly acidic pH of 5.7, hydrophobic amino acid residues become exposed to the surrounding medium, enabling them to bind the fluorescent probe 8,1-ANS. At this pH-induced open state, Mn2+ and Ca2+ bind to the manganese-stabilizing protein. The pH values used in this study, 7.2 and 5.7, are typical of the pH found in the thylakoid lumen in the dark and light, respectively. A model is presented in which the manganese-stabilizing protein undergoes a pH-dependent conformational change that in turn influences its capacity to bind calcium and manganese. In this model, the proton-dependent conformational changes of the tertiary structure of the manganese-stabilizing protein are of functional relevance for the regulation of substrate (water) delivery to and product (proton) release from the water-oxidizing complex by forming a proton-sensing proton-transport pathway.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Shutova
authors.forename: Julia
authors.initials: J
authors.lastname: Nikitina
authors.forename: Gintaras
authors.initials: G
authors.lastname: Deikus
authors.forename: Bertil
authors.initials: B
authors.lastname: Andersson
authors.forename: Vyacheslav
authors.initials: V
authors.lastname: Klimov
authors.forename: Göran
authors.initials: G
authors.lastname: Samuelsson
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D002118:Calcium / Q000494:pharmacology*; D004270:DNA, Circular; D003624:Darkness; D006863:Hydrogen-Ion Concentration; D008027:Light; D008345:Manganese / Q000494:pharmacology*; D008956:Models, Chemical; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000187:drug effects / Q000528:radiation effects; D011487:Protein Conformation / Q000187:drug effects*; D017510:Protein Folding; D013050:Spectrometry, Fluorescence
chemical_list: D000817:Anilino Naphthalenesulfonates; D004270:DNA, Circular; D045332:Photosystem II Protein Complex; C054266:photosystem II manganese-stabilizing protein; D008345:Manganese; C027132:1-anilino-8-naphthalenesulfonate; D002118:Calcium