The Antimicrobial Peptide Gramicidin S Permeabilizes Phospholipid Bilayer Membranes Without Forming Discrete Ion Channels

Abstract

We examined the permeabilization of lipid bilayers by the β-sheet, cyclic antimicrobial decapeptide gramicidin S (GS) in phospholipid bilayers formed either by mixtures of zwitterionic diphytanoylphosphatidylcholine and anionic diphytanoylphosphatidylglycerol or by single zwitterionic unsaturated phosphatidylcholines having various hydrocarbon chain lengths, with and without cholesterol. In the zwitterionic bilayers formed by the phosphatidylcholines, without or with cholesterol, the peptide concentrations and membrane potentials required to initiate membrane permeabilization vary little as function of bilayer thickness and cholesterol content. In all the systems tested, the GS-induced transient ion conductance events exhibit a broad range of conductances, which are little affected by the bilayer composition or thickness. In the zwitterionic phosphatidylcholine bilayers, the effect of GS does not depend on the polarity of the transmembrane potential; however, in bilayers formed from mixtures of phosphatidylcholines and anionic phospholipids, the polarity of the transmembrane potential becomes important, with the GS-induced conductance events being much more frequent when the GS-containing solution is positive relative to the GS-free solution. Overall, these results suggest that GS does not form discrete, well-defined, channel-like structures in phospholipid bilayers, but rather induces a wide variety of transient, differently sized defects which serve to compromise the bilayer barrier properties for small electrolytes.

Minor sequence modifications in temporin B cause drastic changes in antibacterial potency and selectivity by fundamentally altering membrane activity

“…49-51 Previous works have applied this technique to investigate the mode of action of AMPs. [52][53][54][55][56][57][58][59] In particular, the three main membrane-activity models described in the introduction can be distinguished. 52 This protocol involved the use of a microperfusion system on a standard pipette patch-clamp set up and mammalian cells.…”

Chemotherapy Drugs Form Ion Pores in Membranes Due to Physical Interactions with Lipids

“…The point count plot (presented in Figure S2.A) shows that the conductance events do not correspond to discrete current levels with discrete conductance values. These current levels appeared with various possible conductance values, similarly to events observed due to GS (24). Although no major qualitative difference between TCC-and TXL-induced membrane permeabilization was observed, TXL-induced current levels covered a relatively lower conductance range than those for TCC.…”

“…The time-dependent change in the TCC ⁄ TXL pore conductance rules out the possibility of channel formation of the types represented by linear b-helix gA or barrel-stave Alm channels (19,20). Although the point count plots (see the right-hand panel of Figure S2.A) resemble random events observed for GS, which represent defects (24), fine tuning of the conductance events (see Figure 1) suggests that they are long-lived, not just transient (24) but with no fixed conductance. No such time-dependent transitions between non-zero current levels as observed in CD-induced discrete conductance events (see Figure 1) are found in GS-induced defects.…”

“…In a high-resolution plot (shown on the right-hand side of the arrow) of a single event only showing individual points (in Origin 8.5 plot), we observe all points (open circle) with increasing ⁄ decreasing corresponding values of conductance, respectively, at both left and right lateral sides of the chemotherapy drug-induced triangular conductance events. The lower panel (A) illustrates rectangular-shape conductance events in gA and Alm channels [see e.g.,(24)]. gA channel activity was recorded at 200 mV and Alm at 150 mV.…”

In vitro study of the antibacterial effect of the bacteriophage T5 thermostable endolysin on Escherichia coli cells

“…The authors of the publication (Liou et al 2015) believe that the increased size of the pores is a result of the antibiotic-induced formation of hydroxyl radicals and the subsequent oxidation of membrane components. It was shown earlier that gramicidin S, a cyclic gramicidin derivative, did not form discrete channels in the lipid bilayer as well; instead, it gave rise to defects of various sizes, which were hardy influenced by the composition and thickness of the membrane (Ashrafuzzaman et al 2008). The concentrations of gramicidin S used in those experiments were in the range of 0Á1-10 lmol l À1 , which is a hundred times lower than its lytic concentration.…”