Klebsazolicin inhibits 70S ribosome by obstructing the peptide exit tunnel.

Whereas screening of the small-molecule metabolites produced by most cultivatable microorganisms often results in the rediscovery of known compounds, genome-mining programs allow researchers to harness much greater chemical diversity, and result in the discovery of new molecular scaffolds. Here we report the genome-guided identification of a new antibiotic, klebsazolicin (KLB), from Klebsiella pneumoniae that inhibits the growth of sensitive cells by targeting ribosomes. A ribosomally synthesized post-translationally modified peptide (RiPP), KLB is characterized by the presence of a unique N-terminal amidine ring that is essential for its activity.