Guanidino groups greatly enhance the action of antimicrobial peptidomimetics against bacterial cytoplasmic membranes

Abstract

A promising class of potential new antibiotics are the antimicrobial peptides or their synthetic mimics. Herein we assess the effect of the type of cationic side chain (i.e., guanidino vs. amino groups) on the membrane perturbing mechanism of antimicrobial α-peptide–β-peptoid chimeras. Two separate Langmuir monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG) and lipopolysaccharide Kdo2-lipid A were applied to model the outer membranes of Gram-positive and Gram-negative bacteria, respectively. We report the results of the measurements using an array of techniques, including high-resolution synchrotron surface X-ray scattering, epifluorescence microscopy, and in vitro antimicrobial activity to study the molecular mechanisms of peptidomimetic interaction with bacterial membranes. We found guanidino group-containing chimeras to exhibit greater disruptive activity on DPPG monolayers than the amino group-containing analogues. However, this effect was not observed for lipopolysaccharide monolayers where the difference was negligible. Furthermore, the addition of the nitrobenzoxadiazole fluorophore did not reduce the insertion activity of these antimicrobials into both model membrane systems examined, which may be useful for future cellular localization studies.

Investigating the nucleic acid interactions of histone‐derived antimicrobial peptides

“…Recent work from our lab showed increased antimicrobial activity of the BF2 and DesHDAP1 variants (BF2R and DesHDAP1R) where all cationic residues were replaced with arginine [24]. Similar results have been observed for other systems, particularly in the design of antimicrobial peptidomimetics [43–48]. While arginine residues can also increase membrane interactions, our results here show that the enhanced activity of arginine containing peptides may also be due to their increased ability to target nucleic acids.…”

Probing the disparate effects of arginine and lysine residues on antimicrobial peptide/bilayer association

“…Though the two residues have the same net charge, switching the guanidinium groups of arginine for the amine groups of lysine has been shown to decrease the antimicrobial activity, membrane disruptive ability, and cytotoxicity for many AMPs [8, 9, 7, 10], including tritrpticin [11, 6], human neutrophil peptide 1 [12], and KR-12 [13]. Likewise, synthetic peptidomimetics containing amine side chains were shown to be less active against eight bacterial strains than those containing guanidinium groups and, unlike their guanidinium-containing counterparts, do not disrupt DPPG monolayers [14]. Studies comparing arginine and lysine oligomers have shown that polyarginine enters cells far more efficiently than polylysine [15], and binds more strongly to both POPC and mixed POPC/POPG bilayers [16].…”

Peptoid drug discovery and optimization via surface X‐ray scattering

“…Initially invented by Olsen et al ., this biomimetic framework represents AMP with incorporated N ‐alkyl‐β‐alanine (β‐peptoid) residues (Figure ) . Considering in vitro activities of lysine‐containing chimeras to be highly sensitive toward the overall cationicity, as well as the charge distribution, compounds with lysine‐to‐homoarginine (Lys‐to‐ h Arg) substitution have been designed and their interactions with DPPG and Kdo 2 ‐lipid A monolayers have been probed . The working hypothesis was the guanidine groups of h Arg allow for a stable electrostatic binding to the lipid polar moieties by displacing bivalent cations.…”

“…Using phosphatidylcholine vesicles as a membrane model, it has been shown that peptide‐peptoid chimeras prevent lateral diffusion of lipids in fluid phase by interacting with their head groups . However, GIXD data suggest the involvement of hydrocarbon chains in their mechanism of action against negatively charged DPPG . It needs to be noted that lipid head groups may also affect the molecular packing.…”