Orientation of cecropin A helices in phospholipid bilayers determined by solid-state NMR spectroscopy.
The orientation of the insect antibiotic peptide cecropin A (CecA) in the phospholipid bilayer membrane was determined using (15)N solid-state NMR spectroscopy. Two peptide samples, each specifically labeled with (15)N at Val(11) or Ala(27), were synthesized by solid phase techniques. The peptides were incorporated into phospholipid bilayers, prepared from a mixture of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol, and oriented on glass slides. The (15)N chemical shift solid-state NMR spectra from these uniaxially oriented samples display a single (15)N chemical shift frequency for each labeled residue. Both frequencies are near the upfield end of the (15)N chemical shift powder pattern, as expected for an alpha-helix with its long axis in the plane of the membrane and the NH bonds perpendicular to the direction of the magnetic field. These results support a mechanism of action in which CecA binds to and covers the membrane surface, thereby causing a general destabilization and leakiness of the lipid bilayer membrane. The data are discussed in relation to a proposed mechanism of membrane lysis and bacterial killing via an ion channel activity of CecA.
Marassi
F M
FM
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Opella
S J
SJ
Juvvadi
P
P
Merrifield
R B
RB
D000595:Amino Acid Sequence; D000818:Animals; D000890:Anti-Infective Agents / Q000737:chemistry; D023181:Antimicrobial Cationic Peptides; D055592:Biophysical Phenomena; D001703:Biophysics; D066298:In Vitro Techniques; D019476:Insect Proteins / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D019476:Insect Proteins; D008051:Lipid Bilayers; D010455:Peptides; C031161:cecropin A