The PqqD homologous domain of the radical SAM enzyme ThnB is required for thioether bond formation during thurincin H maturation

Thurincin H is a 31‐residue, ribosomally synthesized bacteriocin originating from the thn operon of Bacillus thuringiensis SF361. It is the only known sactipeptide carrying four thioether bridges between four cysteines and the α‐carbons of a serine, an asparagine and two threonine residues. By analysis of the thn operon and use of in vitro studies we now reveal that ThnB is a radical S ‐adenosylmethionine (SAM) enzyme containing two [4Fe–4S] clusters. Furthermore, we confirm the involvement of ThnB in the formation of the thioether bonds present within the structure of thurincin H. Finally, we show that the PqqD homologous N ‐terminal domain of ThnB is essential for maturation of the thurincin H precursor peptide, but not for the SAM cleavage activity of ThnB.