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

•ThnB is a radical SAM enzyme with two [4Fe–4S] clusters.•The first [4Fe–4S] cluster of ThnB is crucial for radical SAM cleavage.•The second [4Fe–4S] cluster of ThnB is essential for thioether bond formation.•The PqqD-like domain in ThnB is needed for thurincin H precursor modification, not SAM cleavage 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.