Structure-Activity Relationships of Antibacterial Acyl-Lysine Oligomers

Abstract

We describe structure-activity relationships that emerged from biophysical data obtained with a library of antimicrobial peptide mimetics composed of 103 oligoacyllysines (OAKs) designed to pin down the importance of hydrophobicity (H) and charge (Q). Based on results obtained with OAKs displaying minimal inhibitory concentration < or = 3 microM, the data indicate that potent inhibitory activity of the gram-negative Escherichia coli and the gram-positive Staphylococcus aureus required a relatively narrow yet distinct window of HQ values where the acyl length played multiple and critical roles, both in molecular organization and in selective activity. Thus, incorporation of long-but not short-acyl chains within a peptide backbone is shown to lead to rigid supramolecular organization responsible for poor antibacterial activity and enhanced hemolytic activity. However, sequence manipulations, including introduction of a tandem lysine motif into the oligomer backbone, enabled disassembly of aggregated OAKs and subsequently revealed tiny, nonhemolytic, yet potent antibacterial derivatives.

Antibacterial Properties and Mode of Action of a Short Acyl-Lysyl Oligomer

“…The bacteria were cultured in suitable broth medium (brain heart infusion or LB). The MIC was determined using a slightly modified NCLSI microdilution assay (44) to enable comparison with previously characterized OAKs (42)(43)(44)(45)(46). For pH and salt variations, the culture medium was brought to the desired pH by adding NaOH or HCl (1 N) or to the desired saline concentration by adding NaCl to the culture medium.…”

“…Peptidomimetic strategies consisting of peptide backbone modifications and incorporation of unnatural amino acids, aromatic rings (25), and amino fatty acids (43,44) have been proposed as novel building blocks to improve potency by enhancing binding affinity to membranes and to reduce susceptibility to inactivation by serum proteases (39). Oligo-acyl-lysines (OAKs) are among the simpler AMP-mimetic designs, in which the two most important characteristics for AMP activity, hydrophobicity and charge, are represented as tandem repeats of amide-linked fatty acids and lysines (15, 42-44, 46, 48).…”

“…Oligo-acyl-lysines (OAKs) are among the simpler AMP-mimetic designs, in which the two most important characteristics for AMP activity, hydrophobicity and charge, are represented as tandem repeats of amide-linked fatty acids and lysines (15, 42-44, 46, 48). This design was shown to overcome the limitations of conventional AMPs with respect to in vivo efficacy and toxicity (43)(44)(45). Two types of OAKs have been presented so far, each composed of acyl-lysyl (␣ n ) or lysyl-acyl-lysyl (␤ n ) subunits, where n defines the acyl length (43).…”

“…This design was shown to overcome the limitations of conventional AMPs with respect to in vivo efficacy and toxicity (43)(44)(45). Two types of OAKs have been presented so far, each composed of acyl-lysyl (␣ n ) or lysyl-acyl-lysyl (␤ n ) subunits, where n defines the acyl length (43). In previous studies, the ␣-OAKs C 12 K-7␣ 8 (44) and C 12 K-5␣ 8 (46) showed potent antibacterial activity against most gram-negative strains tested, both in vitro and in vivo.…”

“…The structure-activity relationships that emerged indicated that the self-assembly properties of excessively hydrophobic OAKs are responsible for poor antibacterial properties and for high hemolytic activity (43). Moreover, the study suggested that the minimal requirements for potent and selective antibacterial activity are embedded in the sequence aminolauryl-[lysyl-aminolauryl-lysyl] 2 (designated NC 12 -2␤ 12 ), the structure of which is depicted in Fig.…”