Exploring RiPP-derived N-acyltransferases for genetically encoded lipopeptide engineering.

Lipopeptides possess diverse bioactivities with widespread uses as antimicrobial drugs and biosurfactants but their biosynthetic engineering remains challenging. Classical lipopeptides (such as daptomycin or surfactin) are biosynthesized by modular, non-ribosomal megasynthetases. An alternative streamlined route to lipopeptides are the ribosomally synthesized and post-translationally modified peptides (RiPPs) derived from gene-encoded precursor proteins. We recently characterized a novel class of post-translational modification enzymes in RiPPs that catalyze fatty acylation of ornithine and lysine side chains. The resulting lipopeptides were termed selidamides. To assess the use of selidamide N-acyltransferases as biocatalysts, we probed the peptide substrate specificity of the model lauroyl-transferase KspN from kamptornamide biosynthesis. Nearest-neighbor, lysine-scan, and truncation mutants demonstrated promiscuity for the peptide substrate. As a proof-of-concept toward designer lipopeptides using RiPP biosynthetic principles, we produced sequences mimicking bioactive non-ribosomal lipopeptides and tested their conversion by maturases from the kamptornamide biosynthetic pathway. Ornithines, fatty acyl groups, and lanthionine macrocycles were installed in the mimics as a promising start toward the directed biosynthesis of custom lipopeptides.