Zwitterionic Phospholipids and Sterols Modulate Antimicrobial Peptide-Induced Membrane Destabilization

Abstract

Cationic amphipathic alpha-helical peptides preferentially disrupt anionic lipids in mixed model membranes, potentially causing a catastrophic release of the cell contents or attenuation of the membrane potential. The effective role of such peptides requires considerable discrimination between target and host cells, which is likely to occur at the level of the cell membrane. Here, we explore the roles of a variety of common membrane constituents in mediating the interaction between the antimicrobial peptide pleurocidin and model membranes. We employ intrinsic tryptophan fluorescence and circular dichroism to observe the effect of increasing concentrations of sterol in the membrane on peptide binding, using (2)H solid-state NMR of chain deuterated lipids simultaneously to probe the effective chain disruption of the anionic phospholipid component of the membrane. We show that the degree of ordering of the lipid acyl chains in the membrane is dependent on the nature of the zwitterionic phospholipid headgroup in mixed anionic membranes. Furthermore, the presence of cholesterol and ergosterol increases acyl chain order in the liquid crystalline model membranes, but to differing degrees. Our results show how sterols can protect even negatively charged membranes from the disruptive effects of antimicrobial peptides, thereby providing a molecular view of the differences in sensitivity of various target membranes to linear cationic antibiotic peptides where bacteria (no sterols) are most susceptible, lower eukaryotes including fungi (containing ergosterol) exhibit an intermediate degree of sensitivity, and higher organisms (containing cholesterol) are largely resistant to antimicrobial peptides.

Sterols and membrane dynamics

“…10b,c). Sterols can also protect negatively charged membranes from the disruptive effects of other antimicrobial peptides [37]. This suggests that bacteria (without sterols) are most susceptible to the action of such peptides whereas lower eukaryotes including fungi (containing ergosterol) exhibit an intermediate degree of sensitivity, and higher organisms (containing cholesterol) are largely resistant to antimicrobial peptides.…”

Structural Determinants of Antimicrobial and Antiplasmodial Activity and Selectivity in Histidine-rich Amphipathic Cationic Peptides

“…In particular, we used solid-state 15 N NMR methods on uniformly aligned samples to show that at peptide/lipid ratios where such pores are formed, the peptides adopt an orientation approximately par-allel to the membrane surface (8), in common with a range of other cationic helical antibiotic peptides (11)(12)(13). Furthermore, we used 2 H NMR of chain deuterated lipids in mixed model membranes to show that cationic pleurocidin strongly destabilizes anionic lipid acyl chains, in preference to zwitterionic lipids, indicating that such peptides are capable of causing local membrane disruption (8) and pore formation (14) while the membrane remains otherwise intact. When using model peptides to study this phenomenon, we showed that histidine-rich cationic amphipathic peptides, such as LAH4, have topologically dependent antibiotic activities (15,16).…”

The Design of Bacteria Strain Selective Antimicrobial Peptides Based on the Incorporation of Unnatural Amino Acids

“…The self-quenching efficiency (Q) for each lipid suspension was set at a minimum value of 80% before it could be used in these investigations. The Q value was calculated using the following equation: Q = (1 -(F 0 /F T )) X 100% where F 0 and F T are the background fluorescence of the lipid suspension and the total fluorescence after the addition of a solution of 10% Triton X, respectively (Jing, Hunter, Hagel, & Vogel, 2003) (Benachir & Lafleur, 1995) (Tachi T, Epand RF, Epand RM, & K., 2002 ) (Mason, Marquette, & Bechinger, 2007).…”