The Dolphin Proline-Rich Antimicrobial Peptide Tur1A Inhibits Protein Synthesis by Targeting the Bacterial Ribosome

Proline-rich antimicrobial peptides (PrAMPs) internalize into susceptible bacteria using specific transporters and interfere with protein synthesis and folding. To date, mammalian PrAMPs have so far only been identified in artiodactyls. Since cetaceans are co-phyletic with artiodactyls, we mined the genome of the bottlenose dolphin Tursiops truncates, leading to the identification of two PrAMPs, Tur1A and Tur1B. Tur1A, which is orthologous to the bovine PrAMP Bac7, is internalized into E. coli without damaging the membranes using the inner membrane transporters SbmA and YjiL/MdM. Furthermore, like Bac7, Tur1A also inhibits bacterial protein synthesis by binding to the ribosome and blocking the transition from the initiation to the elongation phase. By contrast, Tur1B is a poor inhibitor of protein synthesis and appears to act predominantly via disrupting bacterial membranes. An X-ray structure of Tur1A bound within the ribosomal exit tunnel provides a basis to develop these peptides as novel antimicrobial agents.