title: 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-sn-glycero-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 microM, 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 about 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 a 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.
authors.affiliation: Department of Chemistry, 930 North University Avenue, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Khoi Tan
authors.initials: KT
authors.lastname: Nguyen
authors.forename: Stéphanie V
authors.initials: SV
authors.lastname: Le Clair
authors.forename: Shuji
authors.initials: S
authors.lastname: Ye
authors.forename: Zhan
authors.initials: Z
authors.lastname: Chen
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry*; D054806:Magainins; D017550:Spectroscopy, Fourier Transform Infrared; D029867:Xenopus Proteins / Q000737:chemistry*
chemical_list: D023181:Antimicrobial Cationic Peptides; D054806:Magainins; D029867:Xenopus Proteins; C053301:magainin 2 peptide, Xenopus