title: Temperature-dependent coordination in E. coli manganese superoxide dismutase.
abstract: Two different temperature dependences of the manganese(II) high-field electron paramagnetic resonance spectrum of manganese superoxide dismutase from E. coli were observed. In the 25-200 K range, the zero-field interaction steadily decreased with increasing temperature. This was likely due to the thermal expansion of the protein. From these results, it was possible to deduce an approximately r(-)(2.5) dependence of Mn(II) zero-field interaction on ligand-metal distance. At temperatures above 240 K, a distinct six-line component was detected, the amplitude of which decreased with increasing temperature. On the basis of similarities to the six-line spectrum observed for the azide-complexed E. coli manganese superoxide dismutase, the newly detected six-line spectrum was assigned to a hexacoordinate Mn(II) center resulting from the coordination of a nearby water molecule to the normally five-coordinate center. The changes in enthalpy and entropy characterizing the hexacoordinate-pentacoordinate equilibrium in the 240-268 K range were -5 kcal/mol and -24 cal/mol.K, respectively. The structural implications of the zero-field parameters of the newly found hexacoordinate form in comparison to those of the Mn(II) centers in concanavalin-A and manganese-containing R. spheroides photosynthetic reaction centers and the values predicted by the superposition model are discussed.
authors.affiliation: Service de Bioénergétique, DBJC, CNRS URA 2096, CEA Saclay, 91191 Gif-sur-Yvette, France, Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette, France.
authors.forename: Leandro C
authors.initials: LC
authors.lastname: Tabares
authors.forename: Néstor
authors.initials: N
authors.lastname: Cortez
authors.forename: Ileana
authors.initials: I
authors.lastname: Agalidis
authors.forename: Sun
authors.initials: S
authors.lastname: Un
mesh_terms: D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology*; D007501:Iron / Q000737:chemistry; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D013482:Superoxide Dismutase / Q000737:chemistry*; D013696:Temperature
chemical_list: D008345:Manganese; D007501:Iron; D013482:Superoxide Dismutase