Influence of N-acylation of a peptide derived from human lactoferricin on membrane selectivity

Abstract

Increasing numbers of bacterial strains being resistant to conventional antibiotics emphasize the urgent need for new antimicrobial agents. One strategy is based on host defence peptides that can be found in every organism including humans. We have studied the antimicrobial peptide LF11, derived from the pepsin cleavage product of human lactoferrin, known for its antimicrobial and lipid A-binding activity, and peptide C12LF11, the N-lauryl-derivative of LF11, which has owing to the attached hydrocarbon chain an additional hydrophobic segment. The influence of this hydrocarbon chain on membrane selectivity was studied using model membranes composed of dipalmitoylphosphatidylglycerol (DPPG), mimicking bacterial plasma membranes, and of dipalmitoylphosphatidylcholine (DPPC), a model system for mammalian membranes. A variety of biophysical techniques was applied. Thereby, we found that LF11 did not affect DPPC bilayers and showed only moderate effects on DPPG membranes in accordance with its non-hemolytic and weak antimicrobial activity. In contrast, the introduction of the N-lauryl group caused significant changes in the phase behaviour and lipid chain packing in both model membrane systems. These findings correlate with the in vitro tests on methicillin resistant S. aureus, E. coli, P. aeruginosa and human red blood cells, showing increased biological activity of C12LF11 towards these test organisms. This provides evidence that both electrostatic and hydrophobic interactions are crucial for biological activity of antimicrobial peptides, whereas a certain balance between the two components has to be kept, in order not to loose the specificity for bacterial membranes.

Studies on Lactoferricin-derived Escherichia coli Membrane-active Peptides Reveal Differences in the Mechanism of N-Acylated Versus Nonacylated Peptides

“…Nevertheless, an increase in hydrophobicity above a certain threshold value can also result in a loss of membrane specificity, i.e. damage of mammalian cells, as we observed for the N-lauryl derivative of LF11, which exhibited diminished selectivity (6). To further investigate the effect of peptide N-acylation on peptide specificity, different acyl groups were attached to the N terminus of LF11 peptides to increase their specificity toward bacterial versus mammalian cells (6,13,14,44).…”

“…damage of mammalian cells, as we observed for the N-lauryl derivative of LF11, which exhibited diminished selectivity (6). To further investigate the effect of peptide N-acylation on peptide specificity, different acyl groups were attached to the N terminus of LF11 peptides to increase their specificity toward bacterial versus mammalian cells (6,13,14,44). The biophysical studies revealed a chain length-dependent membrane perturbation in agreement with biological activity data with an optimum chain length of eight carbon atoms.…”

“…It is assumed that lactoferricin permeabilizes cell membranes and exerts anti-endotoxic activity by binding to lipopolysaccharides (4). In earlier studies, we demonstrated that the stretch of 11 amino acid residues (LF11, FQWQRNIRKVR-NH 2 ) corresponding to LF residues 21-31 exhibits only weak antibacterial activity against a number of Gram-positive and Gram-negative bacterial strains (5,6). A series of about 150 LF11 mutants was designed with the aim to strengthen membrane-peptide interactions and hence to generate highly antimicrobial and endotoxin-neutralizing peptides, while having no or little antigenic or toxic effect on humans.…”

“…Single or multiple point mutations in LF11 lead to peptide derivatives having up to 30-fold increase in antimicrobial activity (9,10). Another approach was to increase the hydrophobicity by adding a hydrophobic moiety to the peptide (6). For example, Wakabayashi et al (4,11) and Strom et al (12) have shown that N-acylation of derivatives based on a sequence of bovine lactoferricin B (amino acids 17-41) resulted in higher * This work was supported in part by EC-specific RTD Programme Grant QLK2-CT-2002-01001, "Antimicrobial Endotoxin Neutralizing Peptides to Combat Infectious Diseases."…”

Antimicrobial Activity of Lactoferrin-Related Peptides and Applications in Human and Veterinary Medicine

“…In a strategy to improve antimicrobial activity of Lfcin peptides were linked by N-acylation to hydrophobic chains. The derivatives resulted in higher antibacterial activity but also in higher toxicity towards eukaryotic cells [80,81].…”