title: Photoassembly of the manganese cluster in mutants perturbed in the high affinity Mn-binding site of the H2O-oxidation complex of photosystem II.
abstract: The light-driven, oxidative assembly of Mn2+ ions into the H2O-oxidation complex (WOC) of the photosystem II (PSII) reaction center is termed photoactivation and culminates in the formation of the oxygen-evolving (Mn4-Ca) center of the WOC. Initial binding and photooxidation of Mn2+ to the apoprotein is critically dependent upon aspartate 170 of the D1 protein (D1-D170) of the high affinity Mn site [Nixon and Diner (1992) Biochemistry 31, 942-948]. Three O2-evolving mutant strains of Synechocystis, D1-D170E, D1-D170H, and D1-D170V, were studied in terms of the kinetics of photoactivation under both continuous and flashing light. Photoactivation using single turnover flashes revealed D1-D170H and D1-D170V, but not D1-D170E, were prone to form substantial amounts ( approximately 40-50%) of inactive centers ascribed to photoligation of aberrant nonfunctional Mn based upon the reversibility of the inactivation and similarity to previous in vitro results [Chen, C., Kazimir, J., and Cheniae, G. M. (1995) Biochemistry 34, 13511-13526]. On the other hand, D1-D170E lowers the quantum efficiency of photoactivation compared to the wild-type by the largest amount (80% decrease) versus D1-D170H and D1-D170V, which do not produce measurable decreases in quantum efficiency. The low quantum efficiency of photoactivation in D1-D170E is due to the destabilization of photoactivation intermediates. Numerical analysis indicates that the PSII centers in D1-D170E are heterogeneous with respect to photoactivation kinetics and that the majority of centers are characterized by intermediates that decay approximately 10-fold more rapidly than the wild-type control. Additionally, the kinetics of O2 release during the S3-S0 transition was markedly retarded in D1-D170E, in contrast to D1-D170H and D1-D170V, which did not exhibit a discernible slow-down compared to the wild-type.
authors.affiliation: Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: Hong Jin
authors.initials: HJ
authors.lastname: Hwang
authors.forename: Aaron
authors.initials: A
authors.lastname: McLain
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Debus
authors.forename: Robert L
authors.initials: RL
authors.lastname: Burnap
mesh_terms: D001665:Binding Sites; D002478:Cells, Cultured; D019811:Hydroxylamine / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010782:Photolysis; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D019811:Hydroxylamine; D008345:Manganese