Antimicrobial Lipopolypeptides Composed of Palmitoyl Di- and Tricationic Peptides: In Vitro and in Vivo Activities, Self-Assembly to Nanostructures, and a Plausible Mode of Action

Abstract

Antimicrobial lipopeptides are produced nonribosomally in bacteria and fungi during cultivation. They are composed of a cationic or an anionic peptide covalently bound to a specifically modified aliphatic chain. Most of the peptidic moieties have complex cyclic structures. Here we report that conjugation of a palmitic acid to the N-terminus of very short cationic di- and tripeptides composed of all l- and d, l-amino acids endowed them with potent antimicrobial activities. Interestingly, cell specificity was determined by the sequence of the short peptidic chain. Palmitoyllysine served as a control and was inactive toward all microorganisms tested. Replacing an l-amino acid with its d-enantiomer did not affect the activity of the corresponding lipopeptides. Importantly, selected lipopeptides were also potent in vivo in a mouse model of Candida albicans infection. Bacterial leakage experiments and negative staining electron microscopy suggest that their mode of action involves permeation and disintegration of the microorganism's membrane, similar to many long antimicrobial peptides and lipopeptides. Interestingly, each lipopeptide assembled in solution into a nanostructure with a unique morphology which could partially explain differences in their biological activity. Besides adding important information on the parameters necessary for antimicrobial lipopeptides to kill microorganisms, the simple composition of these minilipopeptides and their diverse cell specificities make them attractive candidates for various applications.

Ultrashort Peptide Bioconjugates Are Exclusively Antifungal Agents and Synergize with Cyclodextrin and Amphotericin B

“…Previous studies reported on a family of potent antimicrobial and antifungal ultrashort lipopeptides containing four or fewer amino acids (21,22). The conjugation of fatty acids to otherwise inactive peptides greatly increased the activity and spectrum.…”

“…Both D-and L-amino acids were used, and the sequences were based on previous studies of fatty acid-conjugated peptides (21,22). The lipophilic part of the previously studied lipopeptides consisted of a linear fatty acid, for example, palmitic acid, coupled to the N terminus of the peptide sequence.…”

“…We observed that even small changes in amino acid composition, for example, glycine for alanine residues within a lysine containing tetrapeptide, can alter the antimicrobial potency and have large effects on hemolytic activities. The mode of action of these peptides is the perturbation of the pathogen's membrane (21,22).…”

Cationic Amphiphiles, a New Generation of Antimicrobials Inspired by the Natural Antimicrobial Peptide Scaffold

“…The first results in enhanced permeability, disruption, or perforation of the membrane and is exemplified by melittin, the lipopeptides, and others (40,77,83). This perturbation is observed via dye leakage assays and depolarization studies, which indicate the free transfer of small molecules through the lipid bilayer (16).…”

Short Alkylated Peptoid Mimics of Antimicrobial Lipopeptides

“…Polymyxin B (34) and trichogin (27) possess fatty acid moieties that are known to be integral to their activities. In recent years, development of linear antimicrobial peptides has shifted to ever-shorter peptides for synthetic and pharmacological reasons (15,17,18,22,23), but relatively little work has investigated linear AMPs with hydrophobic tails. Fatty acid tails have been attached to linear antimicrobial peptides that are not normally acylated (4,(19)(20)(21), in some cases endowing inactive cationic peptides with antimicrobial activity.…”