The domain of unknown
function 692 (DUF692) is an emerging family
of post-translational modification enzymes involved in the biosynthesis
of ribosomally synthesized and post-translationally modified peptide
(RiPP) natural products. Members of this family are multinuclear iron-containing
enzymes, and only two members have been functionally characterized
to date: MbnB and TglH. Here, we used bioinformatics to select another
member of the DUF692 family, ChrH, that is encoded in the genomes
of theChryseobacteriumgenus along with a partner
protein ChrI. We structurally characterized the ChrH reaction product
and show that the enzyme complex catalyzes an unprecedented chemical
transformation that results in the formation of a macrocycle, an imidazolidinedione
heterocycle, two thioaminals, and a thiomethyl group. Based on isotopic
labeling studies, we propose a mechanism for the four-electron oxidation
and methylation of the substrate peptide. This work identifies the
first SAM-dependent reaction catalyzed by a DUF692 enzyme complex,
further expanding the repertoire of remarkable reactions catalyzed
by these enzymes. Based on the three currently characterized DUF692
family members, we suggest the family be called multinuclear non-heme
iron dependent oxidative enzymes (MNIOs).