title: Alamethicin in lipid bilayers: combined use of X-ray scattering and MD simulations.
abstract: We study fully hydrated bilayers of two di-monounsaturated phospholipids diC18:1PC (DOPC) and diC22:1PC with varying amounts of alamethicin (Alm). We combine the use of X-ray diffuse scattering and molecular dynamics simulations to determine the orientation of alamethicin in model lipids. Comparison of the experimental and simulated form factors shows that Alm helices are inserted transmembrane at high humidity and high concentrations, in agreement with earlier results. The X-ray scattering data and the MD simulations agree that membrane thickness changes very little up to 1/10 Alm/DOPC. In contrast, the X-ray data indicate that the thicker diC22:1PC membrane thins with added Alm, a total decrease in thickness of 4 A at 1/10 Alm/diC22:1PC. The different effect of Alm on the thickness changes of the two bilayers is consistent with Alm having a hydrophobic thickness close to the hydrophobic thickness of 27 A for DOPC; Alm is then mismatched with the 7 A thicker diC22:1PC bilayer. The X-ray data indicate that Alm decreases the bending modulus (K(C)) by a factor of approximately 2 in DOPC and a factor of approximately 10 in diC22:1PC membranes (P/L approximately 1/10). The van der Waals and fluctuational interactions between bilayers are also evaluated through determination of the anisotropic B compressibility modulus.
authors.affiliation: Biological Physics Group, Physics Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Pan
authors.forename: D Peter
authors.initials: DP
authors.lastname: Tieleman
authors.forename: John F
authors.initials: JF
authors.lastname: Nagle
authors.forename: Norbert
authors.initials: N
authors.lastname: Kucerka
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tristram-Nagle
mesh_terms: D000408:Alamethicin / Q000737:chemistry* / Q000528:radiation effects; D008051:Lipid Bilayers; D008055:Lipids / Q000737:chemistry*; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000737:chemistry*; D011487:Protein Conformation; D012542:Scattering, Radiation; D012997:Solvents; D014965:X-Rays
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D010713:Phosphatidylcholines; D012997:Solvents; D000408:Alamethicin; C017251:1,2-oleoylphosphatidylcholine