title: Utilizing ESEEM spectroscopy to locate the position of specific regions of membrane-active peptides within model membranes.
abstract: Membrane-active peptides participate in many cellular processes, and therefore knowledge of their mode of interaction with phospholipids is essential for understanding their biological function. Here we present a new methodology based on electron spin-echo envelope modulation to probe, at a relatively high resolution, the location of membrane-bound lytic peptides and to study their effect on the water concentration profile of the membrane. As a first example, we determined the location of the N-terminus of two membrane-active amphipathic peptides, the 26-mer bee venom melittin and a de novo designed 15-mer D,L-amino acid amphipathic peptide (5D-L9K6C), both of which are antimicrobial and bind and act similarly on negatively charged membranes. A nitroxide spin label was introduced to the N-terminus of the peptides and measurements were performed either in H2O solutions with deuterated model membranes or in D2O solutions with nondeuterated model membranes. The lipids used were dipalmitoyl phosphatidylcholine (DPPC) and phosphatidylglycerol (PG), (DPPC/PG (7:3 w/w)), egg phosphatidylcholine (PC) and PG (PC/PG (7:3 w/w)), and phosphatidylethanolamine (PE) and PG (PE/PG, 7:3w/w). The modulation induced by the 2H nuclei was determined and compared with a series of controls that produced a reference "ruler". Actual estimated distances were obtained from a quantitative analysis of the modulation depth based on a simple model of an electron spin situated at a certain distance from the bottom of a layer with homogeneously distributed deuterium nuclei. The N-terminus of both peptides was found to be in the solvent layer in both the DPPC/PG and PC/PG membranes. For PE/PG, a further displacement into the solvent was observed. The addition of the peptides was found to change the water distribution in the membrane, making it "flatter" and increasing the penetration depth into the hydrophobic region.
authors.affiliation: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot, Israel 76100.
authors.forename: Raanan
authors.initials: R
authors.lastname: Carmieli
authors.forename: Niv
authors.initials: N
authors.lastname: Papo
authors.forename: Herbert
authors.initials: H
authors.lastname: Zimmermann
authors.forename: Alexey
authors.initials: A
authors.lastname: Potapov
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Shai
authors.forename: Daniella
authors.initials: D
authors.lastname: Goldfarb
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry; D001703:Biophysics / Q000379:methods; D003545:Cysteine / Q000737:chemistry; D003903:Deuterium / Q000737:chemistry; D017666:Deuterium Oxide; D004578:Electron Spin Resonance Spectroscopy; D008055:Lipids / Q000737:chemistry; D008280:Magnetics; D008956:Models, Chemical; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000737:chemistry; D010063:Ovum; D010455:Peptides / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D017434:Protein Structure, Tertiary; D013113:Spin Labels; D013696:Temperature; D013997:Time Factors
chemical_list: D023181:Antimicrobial Cationic Peptides; D008055:Lipids; D010455:Peptides; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010715:Phosphatidylglycerols; D013113:Spin Labels; D015060:1,2-Dipalmitoylphosphatidylcholine; D009569:Nitric Oxide; C483858:phosphatidylethanolamine; D003903:Deuterium; D017666:Deuterium Oxide; D003545:Cysteine