Orientational and Aggregational States of Magainin 2 in Phospholipid Bilayers

Abstract

Magainins from Xenopus skin are antimicrobial peptides with broad spectra, and their action mechanisms are considered to be the permeabilization of bacterial membranes. To elucidate their molecular mechanisms, three analog peptides of magainin 2, each having a Trp residue substituted for Phe at the 5th, 12th, or 16th position, were synthesized, and their interactions with acidic phospholipid membranes were investigated by fluorescence. The Trp substitution did not significantly affect the properties of the parent peptide. The binding isotherms of these peptides to the membranes, which were obtained on the basis of fluorescence changes upon membrane binding of the peptides, were sigmoidal, suggesting the association of the bound peptide molecules. A quantitative analysis indicated that the formed aggregate is a dimer. The observation that the initial rate constant of magainin 2 induced leakage of calcein from liposomes was dependent on the fourth power of the peptide concentration demonstrates the formation of a tetrameric pore. A blue shift and intensity enhancement of Trp fluorescence in the presence of the membranes indicate that those Trp residues are buried in the hydrophobic region of the bilayers. Furthermore, the depths of the Trp residues, which were determined using the n-doxylphosphatidylcholine quenching technique, were about 10 A from the bilayer center irrespective of the peptide aggregational state. Thus, it was concluded that the orientation of the magainin 2 alpha-helix is parallel to the membrane surface. A model of the pore formation will be proposed on the basis of these observations.

Translocation of Analogues of the Antimicrobial Peptides Magainin and Buforin across Human Cell Membranes

“…The peptides preferentially bind to negatively charged phospholipids, forming amphipathic helices (28). Their affinities for mammalian cells, on the surface of which anionic phospholipids are not exposed, have been considered to be low, although weak hydrophobic interaction drives peptide binding (34).…”

“…Peptide Synthesis-The peptide was synthesized by a standard fluoren-9-ylmethoxycarbonyl (Fmoc)-based solid phase method on an Applied Biosystems Model 433A peptide synthesizer, as previously described (28). Fluorescent labeling of the peptides was performed as follows.…”

Release of FGF1 and p40 synaptotagmin 1 correlates with their membrane destabilizing ability

“…Liposomes loaded with fluorescent molecules represent an established model for studying the membrane destabilizing activity of proteins [37]. FGF1 destabilized mixed pG/pC liposomes [29].…”

Antibacterial activity of secretolytin, a chromogranin B‐derived peptide (614–626), is correlated with peptide structure

“…By using a variety of biophysical methods (e.g. fluorescence spectroscopy, NMR), a non-pore mechanism was suggested as a possible mode of action of magainins [31], dermaseptin [24] and insect cecropins [14]. Further support for non-pore mechanism as the mode of action comes from the finding that cecropin-mellitin hybrids as short as 15 amino acids [32], or the 12 amino acid N-terminal analogue of dermaseptin [33] had antibacterial activity similar to that displayed by their intact parent molecules.…”