RESEARCH ARTICLE Structural basis of interprotein electron transfer in bacterial sulfite oxidation Aaron P McGrath1†, Elise L Laming2‡, G Patricia Casas Garcia3, Marc Kvansakul3, J Mitchell Guss2, Jill Trewhella2, Benoit Calmes4,5, Paul V Bernhardt4,5, Graeme R Hanson4,6§, Ulrike Kappler4,5*, Megan J Maher3* 1Structural Biology Program, Centenary Institute, Sydney, Australia; 2School of Molecular Bioscience, University of Sydney, Sydney, Australia; 3Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Australia; 4Centre for Metals in Biology, The University of Queensland, Brisbane, Australia; 5School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Australia; 6Centre for Advanced Imaging, University of Queensland, Brisbane, Australia 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 *For correspondence: detoxification of sulfite is catalyzed by the sulfite-oxidizing enzymes (SOEs), which interact with an
[email protected] (UK); electron acceptor for catalytic turnover. Here, we report the structural and functional analyses of
[email protected] (MJM) the SOE SorT from Sinorhizobium meliloti and its cognate electron acceptor SorU. Kinetic and Present address: † Skaggs thermodynamic analyses of the SorT/SorU interaction show the complex is dynamic in solution, and K ± School of Pharmacy and that the proteins interact with d = 13.5 0.8 mM. The crystal structures of the oxidized SorT and Pharmaceutical Sciences, SorU, both in isolation and in complex, reveal the interface to be remarkably electrostatic, with an University of California, San unusually large number of direct hydrogen bonding interactions.