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Salt‐resistant short antimicrobial peptides

Antimicrobial peptides (AMPs) are promising leads for the development of antibiotics against drug resistant bacterial pathogens. However, in vivo applications of AMPs remain obscure due to salt and serum mediated inactivation. The high cost of chemical synthesis of AMPs also impedes potential clinical application. Consequently, short AMPs resistant toward salt and serum inactivation are desirable for the development of peptide antibiotics. In this work, we designed a 12‐residue amphipathic helical peptide RR12 (R‐R‐L‐I‐R‐L‐I‐L‐R‐L‐L‐R‐amide) and two Trp containing analogs of RR12 namely RR12Wpolar (R‐R‐L‐I‐W‐L‐I‐L‐R‐L‐L‐R‐amide), and RR12Whydro (R‐R‐L‐I‐R‐L‐W‐L‐R‐L‐L‐R‐amide). Designed peptides demonstrated potent antibacterial activity; MIC ranging from 2 to 8 μM, in the presence of sodium chloride (150 mM and 300 mM). Antibacterial activity of these peptides was also detected in the presence of human serum. Designed peptides, in particular RR12 and RR12Whydro, were only poorly hemolytic. As a mode of action; these peptides demonstrated efficient permeabilization of bacterial cell membrane and lysis of cell structure. We further investigated interactions of the designed peptides with lipopolysaccharide (LPS), the major component of the outer membrane permeability barrier of Gram‐negative bacteria. Designed peptides adopted helical conformations in complex with LPS. Binding of peptides with LPS has yielded dissociation the aggregated structures of LPS. Collectively, these designed peptides hold ability to be developed for salt‐resistant antimicrobial compounds. Most importantly, current work provides insights for designing salt‐resistant antimicrobial peptides. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 345–356, 2016.