MSI-78, an Analogue of the Magainin Antimicrobial Peptides, Disrupts Lipid Bilayer Structure via Positive Curvature Strain

Abstract

In this work, we present the first characterization of the cell lysing mechanism of MSI-78, an antimicrobial peptide. MSI-78 is an amphipathic alpha-helical peptide designed by Genaera Corporation as a synthetic analog to peptides from the magainin family. (31)P-NMR of mechanically aligned samples and differential scanning calorimetry (DSC) were used to study peptide-containing lipid bilayers. DSC showed that MSI-78 increased the fluid lamellar to inverted hexagonal phase transition temperature of 1,2-dipalmitoleoyl-phosphatidylethanolamine indicating the peptide induces positive curvature strain in lipid bilayers. (31)P-NMR of lipid bilayers composed of MSI-78 and 1-palmitoyl-2-oleoyl-phosphatidylethanolamine demonstrated that the peptide inhibited the fluid lamellar to inverted hexagonal phase transition of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine, supporting the DSC results, and the peptide did not induce the formation of nonlamellar phases, even at very high peptide concentrations (15 mol %). (31)P-NMR of samples containing 1-palmitoyl-2-oleoyl-phosphatidylcholine and MSI-78 revealed that MSI-78 induces significant changes in the bilayer structure, particularly at high peptide concentrations. At lower concentrations (1-5%), the peptide altered the morphology of the bilayer in a way consistent with the formation of a toroidal pore. Higher concentrations of peptide (10-15%) led to the formation of a mixture of normal hexagonal phase and lamellar phase lipids. This work shows that MSI-78 induces significant changes in lipid bilayers via positive curvature strain and presents a model consistent with both the observed spectral changes and previously published work.

Alpha-helical cationic antimicrobial peptides: relationships of structure and function

“…With the tilt of lipid molecules, the membrane also curves inside to form a hole lined by the lipid head groups and covered by peptides (Yeaman and Yount, 2003;Giuliani et al, 2007). The toroidalpore model is supported by recent studies, which confirmed that these pores are formed by peptides, such as maganins, mellitin and LL-37 (Hallock et al, 2003;Wildman et al, 2003). .…”

Structure, Topology, and Tilt of Cell-Signaling Peptides Containing Nuclear Localization Sequences in Membrane Bilayers Determined by Solid-State NMR and Molecular Dynamics Simulation Studies

“…2D PISEMA experiments were performed on mechanically aligned lipid bilayers containing a 15 N labeled peptide as mentioned in our previous publication (40). A 50 kHz RF field was used in the 1 H channel at on-resonance during the preparation 90° pulse and CP, and a 35.355 kHz offset during the Lee-Goldburg (46) sequence in the SEMA (spin exchange at the magic angle) (39,40) sequence (or the t 1 period).…”

“…All aligned 15 N chemical shift spectra were interpreted with reference to a powder pattern spectrum obtained from MLVs. A spectrum of MLVs containing 3 mole % SKP peptide labeled with 15 N-Leu-11 is given in Figure 6.…”

“…A spectrum of MLVs containing 3 mole % SKP peptide labeled with 15 N-Leu-11 is given in Figure 6. All aligned 15 N spectra showed a single narrow peak suggesting that the embedded peptides have a unique orientation in bilayers; some representative spectra are given in Figures 7 and 8. The measured chemical shift values and the line widths are given in Table 2.…”

“…Since most of the 15 N labeled residues are most likely located in the hydrophobic regions of the bilayer, providing considerably less conformational or dynamic disorder, narrow lines are observed in the spectra of aligned samples. On the other hand, some amphipathic peptides oriented near the surface of bilayers could result in broad lines due to heterogeneous orientation (12,15,58) or narrow lines due to motion (59). The observed line widths range from 1.8 to 6 ppm and did not depend on the RF power of proton decoupling.…”