Ribosomal target-binding sites of antimicrobial peptides Api137 and Onc112 are conserved among pathogens providing new lead structures to develop novel broad-spectrum antibiotics.

Proline-rich antimicrobial peptides expressed in insects are primarily active against Enterobacteriaceae. Mechanistically, they target the bacterial (70S) ribosome after a transporter-based cellular uptake, as revealed for Api137 and Onc112 on Escherichia coli . Initiated by molecular modeling indicating that the Onc112 contact site is conserved among the ribosomes of high-priority pathogens, the ribosome binding of Api137 and Onc112 was studied. The dissociation constants (K d ) of Onc112 were ~75 nmol/L for Escherichia coli , Klebsiella pneumoniae , and Acinetobacter baumannii , 36 nmol/L for Pseudomonas aeruginosa , and 102 nmol/L for Staphylococcus aureus indicating a very promising lead structure to develop broad-spectrum antibiotics. Api137 bound weaker with K d -values ranging from 155 nmol/L to 13 micromol/L. For most bacteria, the antibacterial activities were lower than predicted from the K d -values, which was only partially explained by their ability to enter bacterial cells. Other factors limiting the activity expected from the ribosome binding might be off-target binding.