Fig. 4.

Both clusters of E. coli biotin synthase are involved in the conversion of dethiobiotin to biotin. (A) Escherichia coli biotin synthase BioB (PDB ID: 1R30¹⁹) contains two cofactors: one [4Fe-4S] and one [2Fe-2S] clusters. The [4Fe-4S] cluster is involved in the reduction and the cleavage of SAM molecules leading to the generation of met residues and 5ʹ-dA• radicals. The later are responsible for the insertion of a sulfur atom, coming from the [2Fe-2S] cluster, between the C6 and C9 carbons of the dethiobiotin (DTB) via a radical-based mechanism illustrated in (B).