title: Simulation of S2-state multiline EPR signal in oriented photosystem II membranes: structural implications for the manganese cluster in an oxygen-evolving complex.
abstract: High-quality angular-dependent spectra of multiline electron paramagnetic resonance (EPR) signals from the S2-state Mn cluster in a photosynthetic oxygen-evolving complex (OEC) were obtained for partially oriented photosystem (PS) II membranes, and the magnetic structure of the Mn cluster has been studied by simulation analysis. The angular-dependent multiline spectra were simulated by taking into account the anisotropic properties of both hyperfine tensors of intrinsic Mn ions and g-tensor of the cluster in a tetranuclear model. The best-fit parameters for the simulation indicate that (a) the oxidation state of the S2-state Mn cluster is Mn(III, IV, IV, IV), (b) the electronic orbital configuration of the Mn(III) ion is (dpi)3[dz2(sigma))]1, (c) the effective g-tensor of the Mn cluster and the hyperfine tensor of the Mn(III) ion are axially symmetric, and their principal z-axes are nearly collinear each other, and (d) the z-axis of the dz2 orbital of the Mn(III) ion and the normal of the thylakoid membrane are at an angle of 50.1 +/- 1.8 degrees. The results are compatible with those of the oriented XAFS study [Mukerji, I., et al. (1994) Biochemistry 33, 9712-9721], and indicate that the O-O vector of the putative di-mu-oxo bridged Mn(III)-Mn(IV) dimer unit in the Mn cluster tilts by 43-56 degrees with respect to the normal of thylakoid membrane. A model of the arrangement of the di-mu-oxo bridged Mn(III)-Mn(IV) unit with respect to the thylakoid membrane is proposed.
authors.affiliation: Photosynthesis Research Laboratory, The Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hasegawa
authors.forename: M
authors.initials: M
authors.lastname: Kusunoki
authors.forename: Y
authors.initials: Y
authors.lastname: Inoue
authors.forename: T A
authors.initials: TA
authors.lastname: Ono
mesh_terms: D015502:Absorptiometry, Photon; D002736:Chloroplasts / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005454:Fluorescence Polarization; D007425:Intracellular Membranes / Q000737:chemistry* / Q000378:metabolism; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008432:Mathematical Computing; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D013052:Spectrometry, X-Ray Emission; D018724:Spinacia oleracea
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen