Relationship of Membrane Curvature to the Formation of Pores by Magainin 2

Abstract

Magainin 2, an antimicrobial peptide from the Xenopus skin, kills bacteria by permeabilizing the cell membranes. We have proposed that the peptide preferentially interacts with acidic phospholipids to form a peptide-lipid supramolecular complex pore, which allows mutually coupled transbilayer traffic of ions, lipids, and peptides, thus simultaneously dissipating transmembrane potential and lipid asymmetry [Matsuzaki, K., Murase, O., Fujii, N., and Miyajima, K. (1996) Biochemistry 35, 11361-11368]. In this paper, we examined the effect of membrane curvature strain on pore formation. Magainin effectively forms the pore only in phosphatidylglycerol bilayers at low peptide-to-lipid ratios, well below 1/100. In contrast, the permeabilization of phosphatidylserine, phosphatidic acid, or cardiolipin bilayers occurred at much higher peptide-to-lipid ratios (1/50 to 1/10) with some morphological change of the vesicles. The latter three classes of phospholipids are known to form hexagonal II structures under conditions of reduced interlipid electrostatic repulsions. Incorporation of phosphatidylethanolamine also inhibited the magainin-induced pore formation in the inhibitory order of dioleoylphosphatidylethanolamine > dielaidoylphosphatidylethanolamine. Addition of a small amount of palmitoyllysophosphatidylcholine enhanced the peptide-induced permeabilization of phosphatidylglycerol bilayers. Magainin greatly raised the bilayer to hexagonal II phase transition temperature of dipalmitoleoylphosphatidylethanolamine. These results suggest that the peptide imposes positive curvature strain, facilitating the formation of a torus-type pore, and that the presence of negative curvature-inducing lipids inhibits pore formation.

Mechanism of Lipid Bilayer Disruption by the Human Antimicrobial Peptide, LL-37

“…Peptide and lipids were mixed in 2:1 CHCl 3 /MeOH using 2 mg of lipid for 31 P samples and 100 mg of lipid for 15 N samples. The lipid/peptide mixture was dried under nitrogen and resuspended in 2:1 CHCl 3 /MeOH with a 5:1 mole ratio of naphthalene to lipid/peptide.…”

“…The raw data were converted to molar heat capacity using the CPCalc program provided with the calorimeter and the lipid concentration and molecular weight of each sample along with a partial specific volume of 0.988 mL/g (30). 31 P, 13 C, and 15 N NMR. 31 P, 13 C, and 15 N NMR spectra were acquired using a Varian/Chemagnetics 400 MHz spectrometer with 1 H, 31 P, 13 C, and 15 N frequencies of 400.139, 161.978, 100.618, and 40.551 MHz, respectively.…”

“…31 P, 13 C, and 15 N NMR. 31 P, 13 C, and 15 N NMR spectra were acquired using a Varian/Chemagnetics 400 MHz spectrometer with 1 H, 31 P, 13 C, and 15 N frequencies of 400.139, 161.978, 100.618, and 40.551 MHz, respectively. Home-built, double-resonance, flat-coil probes were used for the mechanically aligned samples with a coil just large enough to hold the samples.…”

“…15 N spectra were referenced as above, and the 13 C spectra were referenced with respect to TMS via adamantane at 29.5 and 38.6 ppm.…”

“…The oriented chemical shift spectra were simulated using the principal values of the chemical shift tensor obtained from the powder pattern to determine the angles θ and φ. The 1-D dipolar-shift powder spectrum was simulated to determine the orientation of the principal axes of the 15 where D NH ) µ o hγ N γ H /8π 2 r NH 3 , and , R, θ, and φ are as defined in Figure 3F. Gaussian line broadening was used in all the simulations.…”