Mechanism of Interaction of Different Classes of Cationic Antimicrobial Peptides with Planar Bilayers and with the Cytoplasmic Membrane ofEscherichia coli

Abstract

Antimicrobial cationic peptides are prevalent throughout nature as part of the intrinsic defenses of most organisms, and have been proposed as a blueprint for the design of novel antimicrobial agents. They are known to interact with membranes, and it has been frequently proposed that this represents their antibacterial target. To see if this was a general mechanism of action, we studied the interaction, with model membranes and the cytoplasmic membrane of Escherichia coli, of 12 peptides representing all 4 structural classes of antimicrobial peptides. Planar lipid bilayer studies indicated that there was considerable variance in the interactions of the peptides with model phospholipid membranes, but generally both high concentrations of peptide and high transmembrane voltages (usually -180 mV) were required to observe conductance events (channels). The channels observed for most peptides varied widely in magnitude and duration. An assay was developed to measure the interaction with the Escherichia coli cytoplasmic membrane employing the membrane potential sensitive dye 3,5-dipropylthiacarbocyanine in the outer membrane barrier-defective E. coli strain DC2. It was demonstrated that individual peptides varied widely in their ability to depolarize the cytoplasmic membrane potential of E. coli, with certain peptides such as the loop peptide bactenecin and the alpha-helical peptide CP26 being unable to cause depolarization at the minimal inhibitory concentration (MIC), and others like gramicidin S causing maximal depolarization below the MIC. We discuss the mechanism of interaction with the cytoplasmic membrane in terms of the model of Matsuzaki et al. [(1998) Biochemistry 37, 15144-15153] and the possibility that the cytoplasmic membrane is not the target for some or even most cationic antimicrobial peptides.

De novo design and in vivo activity of conformationally restrained antimicrobial arylamide foldamers

“…We examined the abilities of the arylamide foldamers, 4d, 4e, and 5b, to depolarize S. aureus membranes, using the membrane potentialsensitive dye DiSC 3 (5). The distribution of this dye between the cell interior and the medium depends on the membrane potential gradient (34,35), leading to an increase in fluorescence intensity in response to a loss of membrane potential. The potassium-selective ionophore valinomycin was used as a positive control.…”

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

“…Another mechanism, similar to the toroidal-pore model and known as the aggregate model, was first proposed by Wu et al (Wu et al, 1999). In this model, AMPs reorient without particular orientation, insert into the membrane, and associate with lipids to form micelle-like complexes.…”

Coordination and transport of alkali metal cations through phospholipid bilayer membranes by hydraphile channels

“…Additional support for this inference was obtained by studying membrane depolarization. This was done by using the membrane dye, 3,3′-dipropylthiadicarbocyanine [DiSC 3 (5)], DiSC, is sensitive to polarized versus depolarized bilayers as reflected in its fluorescence emission [70]. Thus, membrane depolarization was observed when both the hydraphile and a source of cations were present but not when one of these elements was missing.…”