Molecular Interactions between Magainin 2 and Model Membranes in Situ

Abstract

In this paper, we investigated the molecular interactions of Magainin 2 with model cell membranes using Sum Frequency Generation (SFG) vibrational spectroscopy and Attenuated Total Reflectance -Fourier Transform Infrared spectroscopy (ATR-FTIR). Symmetric 1-Palmitoyl-2-Oleoyl-snGlycero-3-[Phospho-rac-(1-glycerol)] (POPG) and 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (POPC) bilayers, which model the bacterial and mammalian cell membranes respectively, were used in the studies. It was observed by SFG that Magainin 2 orients relatively parallel to the POPG lipid bilayer surface at low solution concentrations, around 200 nM. When increasing the Magainin 2 concentration to 800 nM, both SFG and ATR-FTIR results indicate that Magainin 2 molecules insert into the POPG bilayer and adopt a transmembrane orientation with an angle of about 20 degrees from the POPG bilayer normal. For the POPC bilayer, even at a much higher peptide concentration of 2.0 µM, no ATR-FTIR signal was detected. For this concentration on POPC, SFG studies indicated that Magainin 2 molecules adopt an orientation nearly parallel to the bilayer surface, with an orientation angle of 75 degrees from the surface normal. This shows that SFG has a much better detection limit than ATR-FTIR and can therefore be applied to study interfacial molecules with much lower surface coverage. This Magainin 2 orientation study and further investigation of the lipid bilayer SFG signals support the proposed toroidal pore model for the antimicrobial activity of Magainin 2.

More Than a Pore: The Interplay of Pore-Forming Proteins and Lipid Membranes

“…As a consequence, toroidal pore formation by PFPs facilitates the free diffusion of lipid molecules between the two leaflets of the bilayer. According to this, increased flip-flop of lipids was observed in vesicles in the presence of cytolytic peptides such as gramicidin (Classen et al 1987), melittin (Rapson et al 2011), and magainin (Nguyen et al 2009). Transbilayer movement of lipids has been also shown for proteins like colicin E1 (Sobko et al 2004), Bax (Epand et al 2002(Epand et al , 2003, actinoporins (Anderluh et al 2003;Valcarcel et al 2001), and perforin (Metkar et al 2015).…”

Spontaneous Buckling of Lipid Bilayer and Vesicle Budding Induced by Antimicrobial Peptide Magainin 2: A Coarse-Grained Simulation Study

“…12,13 At sufficiently high concentrations, a number of these helical rods are believed to enter the membrane interior, inducing pore formation. 14 Neutron in-plane scattering experiments of multilamellar stacks 8 and vesicles 15 suggested that these inserted peptides form toroidal rather than barrel-stave pores, and the mean diameter of these pores was estimated to be ∼8 nm. 15 The structure of equilibrated pores, however, may not completely explain the mechanism of AMP action adequately, since the exact transient route taken by systems during pore formations likely plays important roles in determining the fate of a particular membrane under attack.…”

Effect of Lipid Composition on the Membrane Orientation of the G Protein-Coupled Receptor Kinase 2–Gβ1γ2 Complex

“…39–44 The design and theoretical background of our SFG spectrometer has been reported previously. 45,46 …”

“…SFG spectra from interfacial proteins were collected at room temperature (24 °C) in a near total internal reflection geometry. 23,45–46 SFG ssp (an s-polarized output sum frequency signal collected with an s-polarized input visible beam and a p-polarized input infrared beam) and ppp spectra were collected in this study. 47–52 We have previously reported on the application of this methodology for the determination of the membrane orientation of proteins by using SFG technique.…”