Interaction of Daptomycin with Lipid Bilayers: A Lipid Extracting Effect

Abstract

Daptomycin is the first approved member of a new structural class of antibiotics, the cyclic lipopeptides. The peptide interacts with the lipid matrix of cell membranes, inducing permeability of the membrane to ions, but its molecular mechanism has been a puzzle. Unlike the ubiquitous membrane-acting host-defense antimicrobial peptides, daptomycin does not induce pores in the cell membranes. Thus, how it affects the permeability of a membrane to ions is not clear. We studied its interaction with giant unilamellar vesicles (GUVs) and discovered a lipid-extracting phenomenon that correlates with the direct action of daptomycin on bacterial membranes observed in a recent fluorescence microscopy study. Lipid extraction occurred only when the GUV lipid composition included phosphatidylglycerol and in the presence of Ca2+ ions, the same condition found to be necessary for daptomycin to be effective against bacteria. Furthermore, it occurred only when the peptide/lipid ratio exceeded a threshold value, which could be the basis of the minimal inhibitory concentration of daptomycin. In this first publication on the lipid extracting effect, we characterize its dependence on ions and lipid compositions. We also discuss possibilities for connecting the lipid extracting effect to the antibacterial activity of daptomycin.

Optical Microscopy of Giant Vesicles as a Tool to Reveal the Mechanism of Action of Antimicrobial Peptides and the Specific Case of Gomesin

“…This point will be discussed later in light of other reports that suggest a peptide-mediated membrane folding. The preferential passage of glucose over sucrose through membrane pores, suggested by the authors as the source of volume increase, has been postulated in other studies as well [61][62][63][64][65][66]. Even though sucrose is indeed larger than glucose (0.…”

“…Therefore, this late decrease cannot have been associated with preferential influx of glucose over efflux of sucrose, since the extension of leakage at that point has been already enough to allow complete leakage of the encapsulated dye, which is bigger than sucrose. In following studies, the aspiration technique was used by the same group to study the effect of other membrane-active molecules on GUVs: the tea catechin EGCg [65], the lipopeptide daptomycin [66], and the cathelicidin peptide LL-37 [64]. In the presence of all these molecules, the vesicle projection length in the micropipette was reported to initially increase and later retract.…”

The action mechanism of daptomycin

“…86 They employed fluorescence microscopy to monitor the interaction of daptomycin with giant unilamellar vesicles (GUVs) composed of DOPC/DOPG (7:3). The vesicles were, at the same time, partially pulled into a tube using constant suction.…”

Mechanism of Action of a Membrane-Active Quinoline-Based Antimicrobial on Natural and Model Bacterial Membranes

“…The putative membrane-targeting of HT61 may provide some explanation for its potency against non-multiplying MRSA [9] , and suggests that its mechanism of action may be similar to those of other membrane-active antibiotics such as daptomycin [10] , cationic antibiotics such as polymyxins B and E (colistin), gramicidin S [11] and cationic antimicrobials, for example chlorhexidine [12] and ceragenins [13] . In general, membrane-active cationic antimicrobials are thought to act by either binding to the headgroups of anionic membrane lipids and disrupting lipid packing to elicit increased permeability of ions and cell metabolites, or to solubilise the membrane in a detergent-like manner [12] .…”