title: Asp157 is required for the function of PsbO, the photosystem II manganese stabilizing protein.
abstract: PsbO, the photosystem II manganese stabilizing protein, contains an aspartate residue [Asp157 (spinach numbering)], which is highly conserved in eukaryotic and prokaryotic PsbOs. The homology model of the PSII-bound conformation of spinach PsbO presented here positions Asp157 in the large flexible loop of the protein. We have characterized site-directed mutants (D157N, D157E, and D157K) of spinach PsbO that were rebound to PsbO-depleted PSII to probe the role of Asp157. Structural data revealed that PsbO Asp157 mutants exhibit near-wild-type solution structure at 25 degrees C, but functional analyses of the mutants showed that these are the first genetically modified PsbO proteins from spinach that combine wild-type PSII binding behavior with significantly impaired O(2) evolution activity; all of the mutants reconstituted approximately 30% of control O(2) evolution activity. PsbO Asp157 has been proposed to be a part of a putative H(2)O/H(+) channel that links the active site of the oxygen-evolving complex with the lumen [De Las Rivas, J., and Barber, J. (2004) Photosynth. Res. 81, 329-343]. Unsuccessful attempts to use chemical rescue to enhance the activity restored by Asp157 mutants could indicate that this residue is not involved in a proton transfer network. It is shown, however, that these mutants are deficient in restoring efficient Cl(-) retention by PSII.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, The University of Michigan,Ann Arbor, Michigan 48109-1048, USA. popelka@umich.edu
authors.forename: Hana
authors.initials: H
authors.lastname: Popelkova
authors.forename: Alan
authors.initials: A
authors.lastname: Commet
authors.forename: Charles F
authors.initials: CF
authors.lastname: Yocum
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain / Q000235:genetics; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D018724:Spinacia oleracea; D013329:Structure-Activity Relationship; D046940:Synechococcus
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C054266:photosystem II manganese-stabilizing protein; D001224:Aspartic Acid; D008345:Manganese; D010100:Oxygen