Association of Radical Chemistry with LanD Flavoprotein Activity for C‐Terminal Macrocyclization of a Ribosomal Peptide by Formation of an Unsaturated Thioether Residue

Abstract LanD flavoproteins catalyze oxidative decarboxylation of the C‐t erminal Cys residue of a peptide to produce an enethiol. This enethiol is highly reactive and can be coupled with an upstream dehydroamino acid through Michael addition to form S ‐[2‐aminovinyl](3‐methyl)cysteine, an unsaturated thioether residue known to be characteristic of an array of C ‐terminally macrocyclized, ribosomally synthesized and posttranslationally modified peptides (RiPPs). Based on a two‐stage bioinformatics mining of posttranslational modifications (PTMs) related to C ‐terminal Cys processing, we report herein that LanD activity can couple with radical S ‐adenosylmethionine chemistry to provide a new unsaturated thioether residue, S ‐[2‐aminovinyl]‐3‐carbamoylcysteine, by conjugating the resultant enethiol with Cβ of the Asn residue in the C ‐terminal NxxC motif of a peptide for macrocyclization. This study furthers our understanding of the variety of PTMs involved in creating the structure diversity of macrocyclic RiPPs.