Bacterial Cytochrome P450-catalyzed Post-translational Macrocyclization

Bacterial cytochrome P450s represent an emerging enzyme family that can modify ribosomally synthesized peptides to generate structurally complex macrocyclic skeletons. However, the functional sequence space of this type of enzyme is largely unexplored. In this study, we conduct a systematic genome mining of small ribosomal peptide-tailoring P450s from genomes of actinobacteria via a precursor-centric, primary sequence-, and structure-guided strategy. We uncovered 1,957 putative P450s, prioritized two representative families for functional study, and characterized two P450 enzymes that can respectively catalyze Tyrosine-to-Tryptophan and Tryptophan-to-Tryptophan crosslinks to form 3-mer or 4-mer macrocycle. These two P450 enzymes exhibit broad substrate selectivity, suggesting a promising starting template for engineering unnatural cyclic peptide construction. Our work expanded the enzymatic catalysis of P450s and could inspire the community to discover hidden peptide-modifying enzymes.