Structure-Activity Relationship Study of Antimicrobial Dermaseptin S4 Showing the Consequences of Peptide Oligomerization on Selective Cytotoxicity

Abstract

To understand how peptide organization in aqueous solution might affect the activity of antimicrobial peptides, the potency of various dermaseptin S4 analogs was assessed against human red blood cells (RBC), protozoa, and several Gram-negative bacteria. Dermaseptin S4 had weak antibacterial activity but potent hemolytic or antiprotozoan effects. K 4 K 20 -S4 was 2-3-fold more potent against protozoa and RBC, yet K 4 K 20 -S4 was more potent by 2 orders of magnitude against bacteria. K 4 -S4 had similar behavior as K 4 K 20 -S4, but K 20 -S4 and analogous negative charge substitutions were as active as dermaseptin S4 or had reduced activity. Binding experiments suggested that potency enhancement was not the result of increased affinity to target cells. In contrast, potency correlated well with aggregation properties. Fluorescence studies indicated that K 20 -S4 and all negative charge substitutions were as aggregated as dermaseptin S4, whereas K 4 -S4 and K 4 K 20 -S4 were clearly less aggregated. Overall, the data indicated that N-terminal domain interaction between dermaseptin S4 monomers is responsible for the peptide's oligomerization in solution and, hence, for its limited spectrum of action. Moreover, bell-shaped dose-response profiles obtained with bacteria but not with protozoa or RBC implied that aggregation can have dramatic consequences on antibacterial activity. Based on these results, we tested the feasibility of selectivity reversal in the activity of dermaseptin S4. Tampering with the composition of the hydrophobic domains by reducing hydrophobicity or by increasing the net positive charge affected dramatically the peptide's activity and resulted in various analogs that displayed potent antibacterial activity but reduced hemolytic activity. Among these, maximal antibacterial activity was displayed by a 15-mer version that was more potent by 2 orders of magnitude compared with native dermaseptin S4. These results emphasize the notion that peptide-based antibiotics represent a highly modular synthetic antimicrobial system and provide indications of how the peptide's physico-chemical properties affect potency and selectivity.

Synthesis and antimicrobial activity of dermaseptin S1 analogues

“…Cytotoxic activity of the synthesized peptides against human RBC indicated 50% haemolysis (Table 1) at a peptide concentration in excess of 75 lM, in most cases >100 lM, confirming that DS1 is weakly haemolytic, possibly because the N-terminus is only moderately hydrophobic. 15 It is worthy of note that only with the compounds 7, 8 and 15 at a concentration of 100 lM did haemolysis in excess of 30% occur. With the other analogues, at the same concentration, lytic activity was between 4% and 16%.…”

“…15,16 In contrast to other S dermaseptin peptides, the 28-residue dermaseptin S4 is highly toxic to erythrocytes but, as noted by Feder et al 15 and Rydlo et al 16 , reducing hydrophobicity or by increasing the net positive charge improved peptide bioactivity. Shorter derivatives still displayed high antibacterial activity in vitro and in vivo along with a more acceptable toxicity profile against human erythrocytes, albeit still rather high.…”

“…Peptide dose causing 50% lethality (LD 50 ) was assessed. 15 More active compounds were assessed for the MIC against several other bacteria, three Gram-positive (S. aureus ATCC 6538P, S. aureus multi-drug-resistant and Bacillus subtilis ATCC 9466) and four Gram-negative (P. aeruginosa ATCC 15442, P. aeruginosa multi-drug-resistant, B. cepacia 6/06 and Stenotrophomonas maltophilia FC). All results represent the mean values obtained from at least two independent experiments performed in duplicate.…”

The antibiotic activity of cationic linear amphipathic peptides: lessons from the action of leucine/lysine copolymers on bacteria of the class Mollicutes

“…4). Thus, two competing processes probably occur in bacteria and erythrocytes as in the case of artificial membranes [25,42,43]: (a) a progressive increase of the membrane affinity with peptide length; and (b) a drop of activity due to decreased free energy in solution upon oligomer formation. The opposite effects produced by dansylating short or long peptides are consistent with this interpretation.…”

Peptoids that mimic the structure, function, and mechanism of helical antimicrobial peptides

“…The precise nature of AMP-membrane interactions remains controversial and actively debated; a variety of mechanisms have been proposed, including the carpet (4), barrel-stave pore (4), toroidal pore (8), and aggregate (9) models. Nevertheless, a considerable number of structure-activity investigations have elucidated how the physicochemical properties of these molecules relate to their biological activities (4,7,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”