MioC is an FMN-binding protein that is essential for Escherichia coli biotin synthase activity in vitro

Biotin synthase is required for the conversion of dethiobiotin to biotin an d requires a number of accessory proteins and small molecule cofactors for activity in vitro. We have previously identified two of these proteins as f lavodoxin and ferredoxin (flavodoxin) NADP(+) reductase. We now report the identification of MioC as a third essential protein, together with its clon ing, purification, and characterization. Purified MioC has a UV-visible spe ctrum characteristic of a flavoprotein and contains flavin mononucleotide. The presence of flavin mononucleotide and the primary sequence similarity t o flavodoxin suggest that. MioC may function as an electron transport prote in. The role of MioC in the biotin synthase reaction is discussed, and the structure and function of MioC is compared with that of flavodoxin.