Structural basis of interprotein electron transfer in bacterial sulfite oxidation
Aaron P McGrath,
Elise L Laming,
G Patricia Casas Garcia,
Marc Kvansakul,
J Mitchell Guss,
Jill Trewhella,
Benoit Calmes,
Paul V Bernhardt,
Graeme R Hanson,
Ulrike Kappler,
Megan J Maher
Affiliations
Aaron P McGrath
Structural Biology Program, Centenary Institute, Sydney, Australia
Elise L Laming
School of Molecular Bioscience, University of Sydney, Sydney, Australia
G Patricia Casas Garcia
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia
Marc Kvansakul
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia
J Mitchell Guss
School of Molecular Bioscience, University of Sydney, Sydney, Australia
Jill Trewhella
School of Molecular Bioscience, University of Sydney, Sydney, Australia
Benoit Calmes
Centre for Metals in Biology, The University of Queensland, Brisbane, Australia; School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia
Paul V Bernhardt
Centre for Metals in Biology, The University of Queensland, Brisbane, Australia; School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia
Graeme R Hanson
Centre for Metals in Biology, The University of Queensland, Brisbane, Australia; Centre for Advanced Imaging, University of Queensland, Brisbane, Australia
Ulrike Kappler
Centre for Metals in Biology, The University of Queensland, Brisbane, Australia; School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia
Megan J Maher
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia
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.
