In Escherichia coli, sulfite reductase is a two-component oxidoreductase that moves six

electrons from three NADPH molecules to reduce sulfite to sulfide for building biomass. We are interested in understanding how the two subunits interact and undergo dramatic conformational changes to elicit such a large volume electron transfer. We use a combination of X-ray crystallography, cryo-EM, and small angle neutron scattering to study this unique enzyme.

The metalloenzyme component of sulfite reductase uses a Fe4-S4 cluster that is covalently bound to a heme-like porphyrinoid called siroheme. We are also interested in understanding the mechanism by which siroheme is produced in proteobacteria, which uses a multifunctional enzyme called CysG to catalyze the three chemical steps needed to synthesize siroheme. We are also interested in studying other bacterial systems that use siroheme for sulfur metabolism like Mycobacterium tuberculosis and Bacillus subtilis.