We describe peptidomimetic oligomers that show rapid, nonhemolytic, broad-spectrum bactericidal properties in mice and do not induce the emergence of resistance. The oligomers contain acyl chains, which prevent the formation of stable secondary structure. This design appears advantageous over conventional antimicrobial peptides with respect to in vivo efficacy and safety, and may provide a convenient platform for the development of peptide antibiotics.

Bactericidal properties were recently shown to emerge from hydrophobicity and charge buildup in oligo-acyl-lysine (OAK) peptide mimetics. Toward understanding the attributes that govern the activity of this novel antimicrobial system, we compared the functional and mechanistic properties of a known octamer and a newly generated hexamer analog. The data provide strong evidence for multiple similarities that included high tissue stability, low hemolysis, large-spectrum antibacterial activity in vitro, and the ability to prevent Escherichia coli-induced mortality in vivo. Despite these similarities, however, the octamer mode of action involved membrane disruption, unlike the hexamer, which acted predominantly through inhibition of DNA functions with characteristically slower bactericidal kinetics. Collectively, the data support the view that the analogous OAKs induced bacterial death by distinct mechanisms and further suggest that relatively minor differences in the sequence of host defense peptides are responsible for selecting one mechanism over another, possibly in conjunction with differential binding affinities to the external and/or cytoplasmic membrane.

Significance Rapid degradation of newly synthesized proteins, followed by presentation of the resulting peptides by the MHC molecules, serves as an early alert for the immune system during pathogen infection. This study defines the relative contribution to the MHC peptidome of defective ribosome products (DRiPs), which are newly synthesized and rapidly degraded proteins, vs. mature proteins, degraded at the end of their functional lifetimes (retirees). The rates of synthesis of the individual MHC peptides and their source proteins were followed using stable isotope labeling and quantitative proteomics and peptidomics analyses. We conclude that DRiPs are a significant source of MHC peptides. Many of these DRiPs are misassembled surplus subunits of protein complexes and therefore are degraded soon after synthesis.

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