S51 family peptidases provide resistance to peptidyl-nucleotide antibiotic McC

Microcin C-like compounds are natural Trojan horse peptide-nucleotide antibiotics produced by diverse bacteria. The ribosomally-synthesized peptide parts of these antibiotics are responsible for their facilitated transport into susceptible cells. Once inside the cell, the peptide part is degraded, releasing the toxic payload, an isoaspartyl-nucleotide that inhibits aspartyl-tRNA synthetase, an enzyme essential for protein synthesis. Bacteria that produce microcin C-like compounds have evolved multiple ways to avoid self-intoxication. Here, we describe a new strategy through the action of S51 family peptidases, which we name MccG. MccG cleaves the toxic isoaspartyl-nucleotide rendering it inactive. While some MccG homologs are encoded in gene clusters responsible for McC-like compounds biosynthesis, most are encoded by stand-alone genes whose products may provide basal level of resistance to peptide-nucleotide antibiotics in phylogenetically distant bacteria. SIGNIFICANCEWe identified a natural substrate for a major phylogenetic clade of poorly characterized S51 family proteases from bacteria. We show that these proteins can contribute to basal level of resistance to an important class of natural antibiotics.