Mutagenesis of the proposed iron-sulfur cluster binding ligands in Escherichia coli biotin synthase.

Biotin synthase (BioB) is a member of a family of enzymes that includes anaerobic ribonucleotide reductase and pyruvate formate lyase activating enzyme. These enzymes all use S-adenosylmethionine during turnover and contain three highly conserved cysteine residues that may act as ligands to an iron-sulfur cluster required for activity. Three mutant enzymes of BioB have been made, each with one cysteine residue (C53, 57, 60) mutated to alanine. All three mutant enzymes were inactive, but they still exhibited the characteristic UV-visible spectrum of a [2Fe-2S]2+ cluster similar to that of the wild-type enzyme.