All-D amino acid-containing channel-forming antibiotic peptides.

Abstract

The D enantiomers of three naturally occurring antibiotics-cecropin A, magainin 2 amide, and melittin-were synthesized. In addition, the D enantiomers of two synthetic chimeric cecropin-melittin hybrid peptides were prepared. Each D isomer was shown by circular dichroism to be a mirror image of the corresponding L isomer in several solvent mixtures. In 20% hexafluoro-2-propanol the peptides contained 43-75% a-helix. The all-D peptides were resistant to enzymatic degradation. The peptides produced single-channel conductances in planar lipid bilayers, and the D and L enantiomers caused equivalent amounts of electrical conductivity. All of the peptides were potent antibacterial agents against representative Gram-negative and Gram-positive species. The D and L enantiomers of each peptide pair were equally active, within experimental error. Sheep erythrocytes were lysed by both D-and L-melittin but not by either isomer of cecropin A, magainin 2 amide, or the hybrids cecropin A-(1-13)-melittin-(1-13)-NH2 or cecropin A-(1-8)-melittin-(1-18)-NH2. The infectivity of the bloodstream form of the malaria parasite Plasmodium falciparum was also inhibited by the D and L hybrids. It is suggested that the mode of action of these peptides on the membranes of bacteria, erythrocytes, plasmodia, and artificial lipid bilayers may be similar and involves the formation of ion-channel pores spanning the membranes, but without specific interaction with chiral receptors or enzymes.The cecropins (1, 2) and several other antibiotic peptides of the animal kingdom, including defensins (3), magainins (4), and the bee venom toxin melittin (5), are thought to function through the formation of ion channels in lipid membranes. This idea has been based on recent studies of electrical conductivity in artificial lipid bilayers (3,(6)(7)(8), where activity is a function of the structure of the peptide and the composition of the membrane lipids. The bilayer lipids and cell membranes are chiral and contain many asymmetric centers. It has been generally assumed that the chirality of the membrane would require a specific chirality ofthe peptide for it to be active, in much the same way that peptide hormones are required to fit with the conformation of their natural receptors or for a substrate and enzyme to form a tight stereospecific complex. However, we have suggested that these peptide antibiotics can exert their effect without requiring a specific target receptor on the cell membrane (7, 9).The purpose of the present study was to test this assumption by the synthesis of the all-D enantiomers of several natural, all-L peptide antibiotics and some of their active analogs. These D stereoisomers would be expected to assume equivalent, but mirror image, conformations when placed in the same environment as the all-L peptides. If a close molecular contact with the chiral components of the cell membrane is required, the D enantiomers would be expected to be inactive. However, if the interaction of the peptide with the membrane is only between achiral...

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

“…Enantiomeric forms of AMPs with D-amino acids only were used to investigate this membrane-binding mechanism (Wade et al, 1990;De Lucca et al, 2000;Bland et al, 2001). However, many studies illustrated that D-amino acid peptides have equal activities with their L-enantiomers (Wade et al, 1990;Hong et al, 1999;Wakabayashi et al, 1999;De Lucca et al, 2000;Bland et al, 2001;Hamamoto et al, 2002;Elmquist and Langel, 2003), suggesting that the antimicrobial mechanism of these peptides does not involve a stereoselective interaction with a chiral enzyme, lipid or protein receptor. However, some data indicate that the D-form AMPs have enhanced antimicrobial activity in vitro and in vivo due to higher stability against proteolysis degradation, which suggests higher clinical therapeutic potential (Vunnam et al, 1998;Chen et al, 2006;Jung et al, 2007).…”

Interaction and Lipid-Induced Conformation of Two Cecropin−Melittin Hybrid Peptides Depend on Peptide and Membrane Composition

“…46 Results are in good agreement with those previously reported for these peptides under similar conditions (HFIP 12% (v/v) in buffer). 8,47 Spectra showed that CA(1-7)M(2-9) adopted a randomcoil structure in buffer, characterized by a minimum at ∼198 nm. In the presence of DMPC liposomes ( Figure 4A), there was a gradual red shift of the λ max of this negative band, which increased with lipid concentration.…”

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

“…Nevertheless, the precise mode of action of these antibacterial peptides is not yet fully understood. It has been suggested that the antibacterial activity appears to be due to the permeation of membranes via peptide-lipid interaction, rather than to receptor-mediated recognition [28,29]. To understand the structural requirements for this antibacterial activity, the enianto, retro, and retroenianto isomers of hybrid analogs of cecropin were synthesized [30].…”