title: The PsbU subunit of photosystem II stabilizes energy transfer and primary photochemistry in the phycobilisome-photosystem II assembly of Synechocystis sp. PCC 6803.
abstract: The PsbU subunit of photosystem II (PSII) is one of three extrinsic polypeptides associated with stabilizing the oxygen evolving machinery of photosynthesis in cyanobacteria. We investigated the influence of PsbU on excitation energy transfer and primary photochemistry by spectroscopic analysis of a PsbU-less (or deltaPsbU) mutant. The absence of PsbU was found to have multiple effects on the excited state dynamics of the phycobilisome and PSII. DeltaPsbU cells exhibited decreased variable fluorescence when excited with light absorbed primarily by allophycocyanin but not when excited with light absorbed primarily by chlorophyll a. Fluorescence emission spectra at 77 K showed evidence for impaired energy transfer from the allophycocyanin terminal phycobilisome emitters to PSII. Picosecond fluorescence decay kinetics revealed changes in both allophycocyanin and PSII associated decay components. These changes were consistent with a decrease in the coupling of phycobilisomes to PSII and an increase in the number of closed PSII reaction centers in the dark-adapted deltaPsbU mutant. Our results are consistent with the assumption that PsbU stabilizes both energy transfer and electron transport in the PBS/PSII assembly.
authors.affiliation: Department of Biological Sciences, Brock University, St. Catharines, Ontario L2S 3A1, Canada.
authors.forename: John
authors.initials: J
authors.lastname: Veerman
authors.forename: Fiona K
authors.initials: FK
authors.lastname: Bentley
authors.forename: Julian J
authors.initials: JJ
authors.lastname: Eaton-Rye
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Sergei
authors.initials: S
authors.lastname: Vasil'ev
authors.forename: Doug
authors.initials: D
authors.lastname: Bruce
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D003624:Darkness; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D004735:Energy Transfer; D005453:Fluorescence; D020868:Gene Silencing; D007700:Kinetics; D008027:Light; D008034:Lincomycin / Q000494:pharmacology; D016254:Mutagenesis, Insertional; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000502:physiology*; D045524:Phycobilisomes / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; C107126:PsbU protein, Synechocystis; D002734:Chlorophyll; D008034:Lincomycin; D010100:Oxygen; D000077194:Chlorophyll A