title: Structural basis of interprotein electron transfer in bacterial sulfite oxidation.
abstract: Interprotein electron transfer underpins the essential processes of life and relies on the formation of specific, yet transient protein-protein interactions. In biological systems, the detoxification of sulfite is catalyzed by the sulfite-oxidizing enzymes (SOEs), which interact with an electron acceptor for catalytic turnover. Here, we report the structural and functional analyses of the SOE SorT from Sinorhizobium meliloti and its cognate electron acceptor SorU. Kinetic and thermodynamic analyses of the SorT/SorU interaction show the complex is dynamic in solution, and that the proteins interact with Kd = 13.5 ± 0.8 μM. The crystal structures of the oxidized SorT and SorU, both in isolation and in complex, reveal the interface to be remarkably electrostatic, with an unusually large number of direct hydrogen bonding interactions. The assembly of the complex is accompanied by an adjustment in the structure of SorU, and conformational sampling provides a mechanism for dissociation of the SorT/SorU assembly.
authors.affiliation: Structural Biology Program, Centenary Institute, Sydney, Australia.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: McGrath
authors.affiliation: School of Molecular Bioscience, University of Sydney, Sydney, Australia.
authors.forename: Elise L
authors.initials: EL
authors.lastname: Laming
authors.affiliation: Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: G Patricia
authors.initials: GP
authors.lastname: Casas Garcia
authors.affiliation: Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Marc
authors.initials: M
authors.lastname: Kvansakul
authors.affiliation: School of Molecular Bioscience, University of Sydney, Sydney, Australia.
authors.forename: J Mitchell
authors.initials: JM
authors.lastname: Guss
authors.affiliation: School of Molecular Bioscience, University of Sydney, Sydney, Australia.
authors.forename: Jill
authors.initials: J
authors.lastname: Trewhella
authors.affiliation: Centre for Metals in Biology, The University of Queensland, Brisbane, Australia.|School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia.
authors.forename: Benoit
authors.initials: B
authors.lastname: Calmes
authors.affiliation: Centre for Metals in Biology, The University of Queensland, Brisbane, Australia.|School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Bernhardt
authors.affiliation: Centre for Metals in Biology, The University of Queensland, Brisbane, Australia.|Centre for Advanced Imaging, University of Queensland, Brisbane, Australia.
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Hanson
authors.affiliation: Centre for Metals in Biology, The University of Queensland, Brisbane, Australia.|School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kappler
authors.affiliation: Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia.
authors.forename: Megan J
authors.initials: MJ
authors.lastname: Maher
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004579:Electron Transport; D007700:Kinetics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D016962:Sinorhizobium meliloti / Q000737:chemistry / Q000378:metabolism*; D013447:Sulfites / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D013447:Sulfites; D010088:Oxidoreductases
keywords: Sinorhizobium meliloti; biophysics; electron transfer; molybdenum; structural biology; sulfite oxidase