Channel-Forming Activity of Cecropins in Lipid Bilayers: Effect of Agents Modifying the Membrane Dipole Potential

Abstract

Cecropin A (CecA) and cecropin B (CecB) added to one side of a bilayer formed from equimolar mixtures of DOPS and DOPE, DPhPS and DPhPE, or DOPS, DOPE, and Chol leads to the formation of well-defined and well-reproducible ion channels of different conductance levels while cecropin P1 (CecP1) does not induce pore formation at micromolar concentrations. We found three populations of CecA channels: pores with weak cationic selectivity, pores with weak anionic selectivity, and pores that were nonselective. The dipole modifiers, flavonoids and styryl dyes, were used to modulate the channel-forming activity of CecA and CecB. The mean conductance of single CecA channels is affected by the influence of dipole modifiers on the lipid packing in the membrane. A decrease in the membrane dipole potential is accompanied by a decrease in the steady-state transmembrane current induced by CecA and CecB in cholesterol-free and cholesterol-containing bilayers. The observed changes in the channel-forming activity might be caused by an increase in the energy barrier for the interfacial accumulation of cecropin monomers. This finding indicates that the negative pole of the cecropin dipole is inserted into the membrane.

The structure and behavior of the NA-CATH antimicrobial peptide with liposomes

“…The region encompassing these charged residues adopts a helical confirmation. The NA-CATH structure appears to be similar to previous straight α-helical AMPs and there is strong evidence supporting a membrane disruption behavior via membrane thinning, defects, transient pores, and carpet model dissolution [20,23,32,88]. Our fluorescence and microscopy data indicate that NA-CATH functions in a similar manner.…”

“…(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) 0.27 ± 0.08 All heavy atoms (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) 0.92 ± 0. We anticipate that if the peptide were binding strongly with the surface of the liposome or were buried within the membrane, the line-width of the peptide 1 H signals would be substantially broadened due to increased anisotropy.…”

“…According to Lad et al [24] and Gazit et al [87], the helix-break/bend-helix structures allow for the flexibility required to penetrate the bilayer. In contrast, long straight helical AMPs show parallel binding to the membrane leading to its disruption [20,87]. Therefore, the carpet mechanism or transient pores are likely leakage mechanisms for such AMPs.…”

Novel anionic cecropins from the spruce budworm feature a poly-L-aspartic acid C-terminus

“…These two amino acid residues are conserved in Cfcec + but not in Cfcec - (Fig.1D). In addition, the hinge region of cecropins (Gly-Pro) is conserved in Cfcec + 2 and Cfcec - 2 as described by Efimova et al (2014) and provides conformational flexibility (Oh et al, 2000) (Fig.1D). Analysis of amino acid residues of both types of C. fumiferana cecropins suggests that Cfcec + shares many characteristics with HccecA (Table 1).…”

Antimicrobial peptides: a new class of antimalarial drugs?

“…The exact molecular mechanisms of membrane activity of cecropins have been under debate for more than 30 years, with two general models being proposed: formation of transmembrane pores, and the carpet model ( Melo et al, 2009 ). A recent study demonstrates that cecropins A and B produce well-defined ion channels of different conductance levels in bilayer lipid membranes; further increase in peptide concentration causes destabilization and subsequent breakdown of the bilayer, showing that formation of pores is a first stage of membrane destabilization by these two cecropins, while accumulation of a dense peptide carpet precedes complete bilayer disintegration ( Efimova et al, 2014 ).…”