title: Site-directed photosystem II mutants with perturbed oxygen-evolving properties. 2. Increased binding or photooxidation of manganese in the absence of the extrinsic 33-kDa polypeptide in vivo.
abstract: Several site-directed photosystem II mutants with substitutions at Asp-170 or in the carboxyterminal region of the D1 polypeptide were characterized in vivo in the absence of the extrinsic 33-kDa polypeptide. Site-directed mutations were constructed in the cyanobacterium Synechocystis sp. PCC 6803. The 33-kDa polypeptide was removed by insertional inactivation of the Synechocystis psbO gene. Mutants were characterized by measuring changes in the yield of variable chlorophyll a fluorescence following a saturating flash or brief illumination in the presence of an electron-transfer inhibitor or following each of a series of saturating flashes in the absence of inhibitor [Chu, H.-A., Nguyen, A. P., & Debus, R. J. (1994) Biochemistry (preceding paper in this issue)]. In the presence of the extrinsic 33-kDa polypeptide, many site-directed mutants contained a significant fraction of photosystem II reaction centers that lacked photooxidizable Mn ions. This fraction decreased dramatically in the absence of the extrinsic 33-kDa polypeptide, even in mutants having a significantly perturbed high-affinity Mn binding site (e.g., in the mutants D170A and D170T). These results show that, in vivo, the extrinsic 33-kDa polypeptide directly or indirectly governs the occupancy of the high-affinity Mn binding site by Mn ions or the ability of bound Mn ions to reduce YZ+.
authors.affiliation: Department of Biochemistry, University of California at Riverside 92521-0129.
authors.forename: H A
authors.initials: HA
authors.lastname: Chu
authors.forename: A P
authors.initials: AP
authors.lastname: Nguyen
authors.forename: R J
authors.initials: RJ
authors.lastname: Debus
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry; D001483:Base Sequence; D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D004563:Electrochemistry; D004579:Electron Transport; D005470:Fluorometry; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010971:Plastoquinone / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D001224:Aspartic Acid; D008345:Manganese; D010971:Plastoquinone; D010100:Oxygen; D000077194:Chlorophyll A