title: EPR study of the oxygen evolving complex in His-tagged photosystem II from the cyanobacterium Synechococcus elongatus.
abstract: The Mn(4)-cluster and the cytochrome c(550) in histidine-tagged photosystem II (PSII) from Synechococcus elongatus were studied using electron paramagnetic resonance (EPR) spectroscopy. The EPR signals associated with the S(0)-state (spin = 1/2) and the S(2)-state (spin = 1/2 and IR-induced spin = 5/2 state) were essentially identical to those detected in the non-His-tagged strain. The EPR signals from the S(3)-state, not previously reported in cyanobacteria, were detectable both using perpendicular (at g = 10) and parallel (at g = 14) polarization EPR, and these signals are similar to those found in plant PSII. In the S(3)-state, near-infrared illumination at 50 K induced a 176-G-wide split signal at g = 2 and signals at g = 5.20 and g = 1.51. These signals differ slightly from those reported in plant PSII [Ioannidis, N., and Petrouleas, V. (2000) Biochemistry 39, 5246-5254]. In accordance with the cited work, the split signal presumably reflects a radical interacting with the Mn(4)-cluster in a fraction of centers, while the g = 5.20 and g = 1.51 signals are tentatively attributed to a high-spin state of the Mn(4)-cluster with zero field splitting parameters different from those in plant PSII, reflecting minor changes in the environment of the Mn(4)-cluster. Biochemical modifications (Sr(2+)/Ca(2+) substitution, acetate and NH(3) treatments) were also investigated. In Sr(2+)-reconstituted PSII, in addition to the expected modified S(2) multiline signal, a signal at g = 5.2 was present instead of the g approximately 4 signal seen in plant PSII. In NH(3)-treated samples, in addition to the expected modified S(2)-multiline signal, a g approximately 4 signal was detected in a small proportion of the reaction centers. This is of note since g approximately 4 spectra arising from the Mn(4)-cluster in the S(2) state have not yet been published in cyanobacterial PSII. The detection of modified S(3)-signals in both perpendicular (at g = 7.5) and parallel (at g = 12) polarization EPR from NH(3)-treated PSII indicate that NH(3) is still bound in the S(3)-state. The acetate-treated PSII behaves essentially as in plant PSII. A study using oriented samples indicated that the heme plane of the oxidized low spin Cytc(550) was perpendicular to the plane of the membrane.
authors.affiliation: Section de Bioénergétique, DBCM, URA CNRS 2096, CEA Saclay, 91191 Gif sur Yvette Cedex, France. boussac@dsvidf.cea.fr
authors.forename: A
authors.initials: A
authors.lastname: Boussac
authors.forename: M
authors.initials: M
authors.lastname: Sugiura
authors.forename: Y
authors.initials: Y
authors.lastname: Inoue
authors.forename: A W
authors.initials: AW
authors.lastname: Rutherford
mesh_terms: D000085:Acetates / Q000737:chemistry; D000643:Ammonium Chloride / Q000737:chemistry; D000458:Cyanobacteria / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D003574:Cytochrome c Group / Q000302:isolation & purification / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006639:Histidine / Q000235:genetics; D007259:Infrared Rays; D010100:Oxygen / Q000378:metabolism*; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex
chemical_list: D000085:Acetates; D003574:Cytochrome c Group; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C064388:oxygen-evolving complex, 33 kDa protein; D000643:Ammonium Chloride; D006639:Histidine; C031732:cytochrome C-550; D010100:Oxygen