Bacterial resistance to clinically used drugs is becoming a major public health concern. Proline-rich antimicrobial peptides (PrAMPs) have kindled renewed interests due to their targeted inhibitory effect on the bacterial protein synthesis, making them effective therapeutic leads, against human pathogens.
Here, we report crystal structures at less than 3 angstroms resolution for a set of PrAMPs, providing insights into their mode of ribosome inactivation and translation inhibition1. These ribosome-inactivating polypeptide (RIPs) sterically interfere with the tRNAs in the A and P sites and also occlude the peptide exit tunnel of the bacterial ribosome. We purified 70S ribosomes from Thermus therophilus, which were then co-crystallized with mRNA, tRNAs and RIPs. We used X-ray on all our crystals containing the complexes to collect diffraction patterns form which we solved the structures by molecular replacement methods. Our biochemical experiments show that the ribosome was effectively stalled during translation right after the initiation step, in presence of the RIPs. This inhibition was also equally potent in cellular environment and was reflected in corresponding hindered cell growth and MIC values in very low micro-molar ranges. We also found from the high-resolution structures, that all of these RIPs have a common mode of binding and their spatial architecture inside the Ribosome overlaps with the binding sites of three well-known classes of antibiotics, a feature that would markedly reduce the probability of appearance of drug resistance. These structures and biochemical data will provide a strong platform for structure-based design of new-generation therapeutics against pathogenic microbes.