Expanded Sequence Space of Radical S-Adenosylmethionine-Dependent Enzymes Involved in Post-translational Macrocyclization.

Ribosomally synthesized and post-translationally modified peptides (RiPPs) represent one of the largest but primarily underexplored natural product families in bacteria. The genetically encoded nature of RiPPs simplifies the prediction and prioritization of their biosynthetic gene clusters (BGCs). We report a small peptide and enzyme co-occurrence analysis workflow (SPECO), which allowed us to identify 32 220 prospective rSAM-catalyzed RiPP BGCs from 161 954 bacterial genomes and prioritize 25 families with new biosynthetic architectures or precursor patterns. We characterized three new enzymes that respectively catalyze cysteine-glycine (BlaB), histidine-aliphatic side chain (ScaB), and tyrosine/histidine-arginine (VguB) cross-links. The cyclophane-forming enzyme ScaB exhibits broad substrate selectivity, allowing it to catalyze diverse triceptide formation. These results demonstrate the strength of the SPECO workflow in discovering new enzymes for peptide macrocyclization.