Insect peptides with improved protease‐resistance protect mice against bacterial infection

Abstract

At a time of the emergence of drug-resistant bacterial strains, the development of antimicrobial compounds with novel mechanisms of action is of considerable interest. Perhaps the most promising among these is a family of antibacterial peptides originally isolated from insects. These were shown to act in a stereospecific manner on an as-yet unidentified target bacterial protein. One of these peptides, drosocin, is inactive in vivo due to the rapid decomposition in mammalian sera. However, another family member, pyrrhocoricin, is significantly more stable, has increased in vitro efficacy against Gram-negative bacterial strains, and if administered alone, as we show here, is devoid of in vitro or in vivo toxicity. At low doses, pyrrhocoricin protected mice against Escherichia coli infection, but at a higher dose augmented the infection of compromised animals. Analogs of pyrrhocoricin were, therefore, synthesized to further improve protease resistance and reduce toxicity. A linear derivative containing unnatural amino acids at both termini showed high potency and lack of toxicity in vivo and an expanded cyclic analog displayed broad activity spectrum in vitro. The bioactive conformation of native pyrrhocoricin was determined by nuclear magnetic resonance spectroscopy, and similar to drosocin, reverse turns were identified as pharmacologically important elements at the termini, bridged by an extended peptide domain. Knowledge of the primary and secondary structural requirements for in vivo activity of these peptides allows the design of novel antibacterial drug leads.

Babesial Vector Tick Defensin againstBabesiasp. Parasites

“…Moreover, longicin appears to be stable in vivo and therefore able to act against Babesia parasites when exported to them. This may be due to its lack of degradation by murine proteases (39). Surprisingly, present therapeutic test results indicate that the efficacy of longicin is superior to that reported for antibabesial drugs commonly used in clinical practice (48).…”

“…Ticks are phylogenetically closer to spiders and scorpions (Arachnida, Chelicerata) than to insects (24,29). Cationic defensin peptides from both spiders and scorpions act as ion channel blockers, and the ion channel recognition site is located in the ␤-sheet of their C termini (39). Longicin may have evolved from a common ancestral peptide resembling spider and scorpion toxins.…”

Mechanism of Escherichia coli Resistance to Pyrrhocoricin

“…Proline-rich antimicrobial peptides (PRAMPs) isolated from mammals and insects represent a promising class of drug candidates exhibiting those features (4)(5)(6)(7)(8). These peptides are important components of the innate immune defense against Gram-negative bacterial infections and, as such, they show very low toxicity toward mammalian cells and good serum stability (4,9).…”

Allosteric Coupling between the Lid and Interdomain Linker in DnaK Revealed by Inhibitor Binding Studies

“…Nontoxicity to mammalian cells and good serum stability of L-PYR-derived peptides make them promising drug candidates in treating emerging/re-emerging antimicrobial-resistant bacterial pathogens (15,35) and highlight the importance of detailed structural characterization of inhibitorprotein interactions with a view to rational drug design. This paper describes the first crystal structures of the E. coli DnaK SBD, truncated at the C terminus (residues 389 to 607), in complex with two L-PYR-derived peptidic inhibitors, one of which (the short peptide) displays nanomolar affinity for nucleotide-free E. coli DnaK (K d [dissociation constant] ϭ 5.5 nM, the lowest that has ever been reported for any peptide [M. Liebscher, unpublished data]).…”