An Acetyltransferase Conferring Self-Resistance of the Producer to Lasso Peptide Antibiotic Lariocidin

The soil microbiome, a reservoir of antibiotic-producing bacteria, also harbors resistance determinants encoded within antibiotic biosynthetic gene clusters (BGCs). Studying self-resistance mechanisms, which have evolved in producers to protect against their own toxic metabolites, provides critical insights into the evolution of resistance and the potential vulnerabilities of new antibiotics and can facilitate the production of natural products in heterologous hosts. Here, we describe the self-resistance mechanism to lariocidin (LAR), a recently discovered lasso peptide antibiotic that inhibits the ribosomal machinery and exhibits antibacterial activity against key pathogens. We identified and characterized an <i>N</i>-acetyltransferase enzyme (LrcE) encoded within the LAR BGC that mediates self-resistance in LAR-producing <i>Paenibacillus</i> sp. M2. LrcE is a member of the GCN5-related <i>N</i>-acetyltransferase (GNAT) superfamily and performs site-specific acetylation of LAR at a critical lysine residue. This modification disrupts ribosomal binding, thereby reducing LAR's antibacterial activity. Using in silico modeling, we predicted a conserved acetyl-CoA-binding motif and an LAR-binding region on LrcE. Bioinformatic analysis revealed LrcE homologues in environmental but not clinically relevant pathogens, suggesting a limited risk of horizontal gene transfer and, therefore, supporting the further development of LAR as a next-generation antibiotic.