Solution Structure and Membrane Interactions of the Antimicrobial Peptide Fallaxidin 4.1a: An NMR and QCM Study

Abstract

The solution structure of fallaxidin 4.1a, a C-terminal amidated analogue of fallaxidin 4.1, a cationic antimicrobial peptide isolated from the amphibian Litoria fallax, has been determined by nuclear magnetic resonance (NMR). In zwitterionic dodecylphosphocholine (DPC) micelles, fallaxidin 4.1a adopted a partially helical structure with random coil characteristics. The flexibility of the structure may enhance the binding and penetration upon interaction with microbial membranes. Solid-state (31)P and (2)H NMR was used to investigate the effects of fallaxidin 4.1a on the dynamics of phospholipid membranes, using acyl chain deuterated zwitterionic dimyristoylphosphatidylcholine (DMPC-d(54)) and anionic dimyristoylphosphatidylglycerol (DMPG) multilamellar vesicles. In DMPC-d(54) vesicle bilayers, fallaxidin 4.1a caused a decrease in the (31)P chemical shift anisotropy (CSA), and a decrease in deuterium order parameters from the upper acyl chain region, indicating increased lipid motion about the phosphate headgroups. Conversely, for DMPC-d(54)/DMPG, two (31)P CSA were observed due to a lateral phase separation of the two lipids and/or differing headgroup orientations in the presence of fallaxidin 4.1a, with a preferential interaction with DMPG. Little effect on the deuterated acyl chain order parameters was observed in the d(54)-DMPC/DMPG model membranes. Real time quartz crystal microbalance analyses of fallaxidin 4.1a addition to DMPC and DMPC/DMPG supported lipid bilayers together with the NMR results indicated transmembrane pore formation in DMPC/DMPG membranes and peptide insertion followed by disruption at a threshold concentration in DMPC membranes. The different interactions observed with "mammalian" (DMPC) and "bacterial" (DMPC/DMPG) model membranes imply fallaxidin 4.1a may be a useful antimicrobial peptide, with preferential cytolytic activity toward prokaryotic organisms at low peptide concentrations (<5 microM).

Mechanism of Four de Novo Designed Antimicrobial Peptides

“…1B I-IV ) changes in the properties of the bilayer during AMP flow and subsequent buffer wash. These changes are quantified by the change in frequency (⌬F) and change in dissipation (⌬D) of an oscillating silica sensor, which is a technique commonly reported in the literature (15,(27)(28)(29)(30)(31)(32). Here, kinetic information is generally used to determine the rates and number of observable stages involved in each mode of action of the AMPs, whereas equilibrium data are related to the final mechanistic changes of the SLB.…”

Specific uptake and interactions of peptide nucleic acid derivatives with biomimetic membranes

“…[23][24][25][26][27][28] Changes in the oscillation frequency of chip (∆f) in QCM-D give information about the mass deposited on the surface, according to the Sauerbrey relationship, for tightly coupled material, the change in frequency (-∆f ) is 110 directly correlated with mass (∆m), where ∆m corresponds to the mass attached to the sensor surface. 48 In addition, the viscoelastic properties of the chip surface can be measured using the change in energy dissipation, ∆D.…”

“…[23][24][25][26][27][28] QCM- 55 D is a highly sensitive, convenient tool for the quantitative and qualitative analysis of biomolecular interactions. [29][30] It allows for real time monitoring of mass and structural changes in the lipid membrane upon their interaction with biomolecules providing unique fingerprints for each peptide.…”

Histidine‐containing host‐defence skin peptides of anurans bind Cu2+. An electrospray ionisation mass spectrometry and computational modelling study

“…Only one of these, the antibiotic peptide fallaxidin 4.1, has had its 3D structure determined by 2D NMR in membrane-mimicking solvents. [50] That unusual structure is shown in Fig. 6, where it can be seen that although K 8 14 Cu loss (which of course does not exclude the possibility of K 14 involvement in the complex).…”

“…We first examined the complexation of caerin 1.8, caerin 1.2 and the Ala 15 synthetic modification of maculatin 1.1 (see Table 1 These peptides were chosen because they are all amphipathic peptides which have helix-hinge-helix structures in membrane-mimicking solvents like trifluoroethanol/water and model lipids. [2,50] The three cations, Cu 2+ , Mg 2+ and Zn 2+ , have very similar ionic radii (namely 74, 72 and 74 pm, respectively [51] ). In principle, caerins 1.8 and 1.2 might bind metals between the two central histidines with the overall structures remaining helix-hinge-helix, but if caerin 1.2 binds metal cations between one of the central His and the Cterminal His, it cannot do this within a helical structure.…”