Deciphering the Mode of Action of the Synthetic Antimicrobial Peptide Bac8c

Abstract

Bac8c (RIWVIWRR-NH 2 ) is an 8-amino-acid peptide derived from Bac2A (RLARIVVIRVAR-NH 2 ), a C3A/ C11A variant of the naturally occurring bovine peptide, bactenecin (also known as bovine dodecapeptide), the smallest peptide with activity against a range of pathogenic Gram-positive and Gram-negative bacteria, as well as yeast. The effects of Bac8c on Escherichia coli were examined by studying its bacteriostatic and bactericidal properties, demonstrating its effects on proton motive force generation, and visually analyzing (via transmission electron microscopy) its effects on cells at different concentrations, in order to probe the complexities of the mechanism of action of Bac8c. Results were consistent with a two-stage model for the Bac8c mode of action. At sublethal concentrations (3 g/ml), Bac8c addition resulted in transient membrane destabilization and metabolic imbalances, which appeared to be linked to inhibition of respiratory function. Although sublethal concentrations resulted in deleterious downstream events, such as methylglyoxal formation and free radical generation, native E. coli defense systems were sufficient for full recovery within 2 h. In contrast, at the minimal bactericidal concentration (6 g/ml), Bac8c substantially but incompletely depolarized the cytoplasmic membrane within 5 min and disrupted electron transport, which in turn resulted in partial membrane permeabilization and cell death.

Small cationic antimicrobial peptides delocalize peripheral membrane proteins

“…The impact of MP196 on cell-wall biosynthesis is illustrated by a reduction in precursor incorporation, promoter activation of cell-wall stress-responsive genes, up-regulation of proteins indicative of cell-wall biosynthesis stress, and loss of cell-wall integrity. Similar observations have been reported for gramicidin S (26) and Bac8c (46). In addition to an indirect effect on cell-wall biosynthesis caused by energy limitation, we found that small cationic peptides affect cell-wall biosynthesis by delocalizing the lipid II biosynthesis protein MurG from the intracellular surface of the membrane.…”

Cytokeratins mediate epithelial innate defense through their antimicrobial properties

“…The 19-mer peptide killed 71.7% and 91.7% of strain 6206 after 5 and 15 minutes, respectively, and 98% of strain 6294 after 15 minutes ( Figure 5D). Antimicrobial proteins or peptides that exert killing effects via inhibition of macromolecular synthesis, i.e., DNA, RNA, and/or protein, generally require at least 30 minutes of exposure for maximal impact on bacterial viability (>90% killing) (32,33). The rapid action of the 19-mer suggested that direct membrane disruption was involved in the mechanism by which it killed P. aeruginosa.…”

Targeting Mycobacterium tuberculosis and Other Microbial Pathogens Using Improved Synthetic Antibacterial Peptides

“…While a single mechanism does not underlie all effects of CAMPs, their bactericidal activities often depend on their abilities to permeabilize membranes by creating pores or disrupting the organization of the lipid bilayer. Partial depolarization of the cytoplasmic membrane by CAMPs interferes with electron transport and oxidative metabolism, leading to cell death (5,6). CAMP binding to ATP may mediate additional effects on metabolism (7)(8)(9)(10).…”