title: Spectroscopic and functional characterizations of cyanobacterium Synechocystis PCC 6803 mutants on and near the heme axial ligand of cytochrome b559 in photosystem II.
abstract: The functional role of cytochrome (cyt) b(559) in photosystem II (PSII) was investigated in H22K alpha and Y18S alpha cyt b(559) mutants of the cyanobacterium Synechocystis sp. PCC6803. H22K alpha and Y18S alpha cyt b(559) mutant carries one amino acid substitution on and near one of heme axial ligands of cyt b(559) in PSII, respectively. Both mutants grew photoautotrophically, assembled stable PSII, and exhibited the normal period-four oscillation in oxygen yield. However, both mutants showed several distinct chlorophyll a fluorescence properties and were more susceptible to photoinhibition than wild type. EPR results indicated the displacement of one of the two axial ligands to the heme of cyt b(559) in H22K alpha mutant reaction centers, at least in isolated reaction centers. The maximum absorption of cyt b(559) in Y18S alpha mutant PSII core complexes was shifted to 561 nm. Y18S alpha and H22K alpha mutant PSII core complexes contained predominately the low potential form of cyt b(559). The findings lend support to the concept that the redox properties of cyt b(559) are strongly influenced by the hydrophobicity and ligation environment of the heme. When the cyt b(559) mutations placed in a D1-D170A genetic background that prevents assembly of the manganese cluster, accumulation of PSII is almost completely abolished. Overall, our data support a functional role of cyt b(559) in protection of PSII under photoinhibition conditions in vivo.
authors.affiliation: Institute of Plant and Microbial Biology, Taiwan International Graduate Program, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Chung-Hsien
authors.initials: CH
authors.lastname: Hung
authors.forename: Hong Jin
authors.initials: HJ
authors.lastname: Hwang
authors.forename: Yung-Han
authors.initials: YH
authors.lastname: Chen
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Chiu
authors.forename: Shyue-Chu
authors.initials: SC
authors.lastname: Ke
authors.forename: Robert L
authors.initials: RL
authors.lastname: Burnap
authors.forename: Hsiu-An
authors.initials: HA
authors.lastname: Chu
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain / Q000502:physiology; D002734:Chlorophyll / Q000235:genetics / Q000378:metabolism; D000077194:Chlorophyll A; D003573:Cytochrome b Group / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000235:genetics / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D020125:Mutation, Missense; D010788:Photosynthesis / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence / Q000379:methods; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003573:Cytochrome b Group; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D006418:Heme; C019313:cytochrome b559; D000077194:Chlorophyll A