title: High-resolution structure of the photosynthetic Mn4Ca catalyst from X-ray spectroscopy.
abstract: The application of high-resolution X-ray spectroscopy methods to study the photosynthetic water oxidizing complex, which contains a unique hetero-nuclear catalytic Mn4Ca cluster, is described. Issues of X-ray damage, especially at the metal sites in the Mn4Ca cluster, are discussed. The structure of the Mn4Ca catalyst at high resolution, which has so far eluded attempts of determination by X-ray diffraction, X-ray absorption fine structure (EXAFS) and other spectroscopic techniques, has been addressed using polarized EXAFS techniques applied to oriented photosystem II (PSII) membrane preparations and PSII single crystals. A review of how the resolution of traditional EXAFS techniques can be improved, using methods such as range-extended EXAFS, is presented, and the changes that occur in the structure of the cluster as it advances through the catalytic cycle are described. X-ray absorption and emission techniques (XANES and Kbeta emission) have been used earlier to determine the oxidation states of the Mn4Ca cluster, and in this report we review the use of X-ray resonant Raman spectroscopy to understand the electronic structure of the Mn4Ca cluster as it cycles through the intermediate S-states.
authors.affiliation: Melvin Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Junko
authors.initials: J
authors.lastname: Yano
authors.forename: Jan
authors.initials: J
authors.lastname: Kern
authors.forename: Yulia
authors.initials: Y
authors.lastname: Pushkar
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sauer
authors.forename: Pieter
authors.initials: P
authors.lastname: Glatzel
authors.forename: Uwe
authors.initials: U
authors.lastname: Bergmann
authors.forename: Johannes
authors.initials: J
authors.lastname: Messinger
authors.forename: Athina
authors.initials: A
authors.lastname: Zouni
authors.forename: Vittal K
authors.initials: VK
authors.lastname: Yachandra
mesh_terms: D002118:Calcium / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman
chemical_list: D045332:Photosystem II Protein Complex; D008345:Manganese; D002118:Calcium