Analysis of the E. coli NifS CsdB protein at 2.0 Å reveals the structural basis for perselenide and persulfide intermediate formation

The Escherichia coli NifS CsdB protein is a member of the homodimeric pyridoxal 5′-phosphate (PLP)-dependent family of enzymes. These enzymes are capable of decomposing cysteine or selenocysteine into l-alanine and sulfur or selenium, respectively. E. coli NifS CsdB has a high specificity for l-selenocysteine in comparison to l-cysteine, suggesting a role for this enzyme is selenium metabolism. The 2.0 Å crystal structure of E. coli NifS CsdB reveals a high-resolution view of the active site of this enzyme in apo-, persulfide, perselenide, and selenocysteine-bound intermediates, suggesting a mechanism for the stabilization of the enzyme persulfide and perselenide intermediates during catalysis, a necessary intermediate in the formation of sulfur and selenium containing metabolites.