title: Glutamate-354 of the CP43 polypeptide interacts with the oxygen-evolving Mn4Ca cluster of photosystem II: a preliminary characterization of the Glu354Gln mutant.
abstract: In the recent X-ray crystallographic structural models of photosystem II, Glu354 of the CP43 polypeptide is assigned as a ligand of the O2-evolving Mn4Ca cluster. In this communication, a preliminary characterization of the CP43-Glu354Gln mutant of the cyanobacterium Synechocystis sp. PCC 6803 is presented. The steady-state rate of O2 evolution in the mutant cells is only approximately 20% compared with the wild-type, but the kinetics of O2 release are essentially unchanged and the O2-flash yields show normal period-four oscillations, albeit with lower overall intensity. Purified PSII particles exhibit an essentially normal S2 state multiline electron paramagnetic resonance (EPR) signal, but exhibit a substantially altered S2-minus-S1 Fourier transform infrared (FTIR) difference spectrum. The intensities of the mutant EPR and FTIR difference spectra (above 75% compared with wild-type) are much greater than the O2 signals and suggest that CP43-Glu354Gln PSII reaction centres are heterogeneous, with a minority fraction able to evolve O2 with normal O2 release kinetics and a majority fraction unable to advance beyond the S2 or S3 states. The S2-minus-S1 FTIR difference spectrum of CP43-Glu354Gln PSII particles is altered in both the symmetric and asymmetric carboxylate stretching regions, implying either that CP43-Glu354 is exquisitely sensitive to the increased charge that develops on the Mn4Ca cluster during the S1-->S2 transition or that the CP43-Glu354Gln mutation changes the distribution of Mn(III) and Mn(IV) oxidation states within the Mn4Ca cluster in the S1 and/or S2 states.
authors.affiliation: Department of Biochemistry, University of California, Riverside, CA 92521, USA.
authors.forename: Melodie A
authors.initials: MA
authors.lastname: Strickler
authors.forename: Hong Jin
authors.initials: HJ
authors.lastname: Hwang
authors.forename: Robert L
authors.initials: RL
authors.lastname: Burnap
authors.forename: Junko
authors.initials: J
authors.lastname: Yano
authors.forename: Lee M
authors.initials: LM
authors.lastname: Walker
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Service
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.forename: Warwick
authors.initials: W
authors.lastname: Hillier
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Debus
mesh_terms: D002118:Calcium / Q000737:chemistry*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D018698:Glutamic Acid / Q000737:chemistry* / Q000235:genetics; D008345:Manganese / Q000737:chemistry*; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics; D017550:Spectroscopy, Fourier Transform Infrared; D046939:Synechocystis / Q000737:chemistry / Q000235:genetics; D013816:Thermodynamics
chemical_list: D004269:DNA, Bacterial; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C083100:photosystem II, chlorophyll binding protein, CP-43; D018698:Glutamic Acid; D008345:Manganese; D010100:Oxygen; D002118:Calcium