Alamethicin aggregation in lipid membranes.
X-ray scattering features induced by aggregates of alamethicin (Alm) were obtained in oriented stacks of model membranes of DOPC(diC18:1PC) and diC22:1PC. The first feature obtained near full hydration was Bragg rod in-plane scattering near 0.11 A(-1) in DOPC and near 0.08 A(-1) in diC22:1PC at a 1:10 Alm:lipid ratio. This feature is interpreted as bundles consisting of n Alm monomers in a barrel-stave configuration surrounding a water pore. Fitting the scattering data to previously published molecular dynamics simulations indicates that the number of peptides per bundle is n = 6 in DOPC and n >or= 9 in diC22:1PC. The larger bundle size in diC22:1PC is explained by hydrophobic mismatch of Alm with the thicker bilayer. A second diffuse scattering peak located at q(r) approximately 0.7 A(-1) is obtained for both DOPC and diC22:1PC at several peptide concentrations. Theoretical calculations indicate that this peak cannot be caused by the Alm bundle structure. Instead, we interpret it as being due to two-dimensional hexagonally packed clusters in equilibrium with Alm bundles. As the relative humidity was reduced, interactions between Alm in neighboring bilayers produced more peaks with three-dimensional crystallographic character that do not index with the conventional hexagonal space groups.
Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Jianjun
J
Pan
Stephanie
S
Tristram-Nagle
John F
JF
Nagle
D000408:Alamethicin / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007473:Ion Channels / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry; D012542:Scattering, Radiation; D014961:X-Ray Diffraction
D007473:Ion Channels; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D000408:Alamethicin; C017251:1,2-oleoylphosphatidylcholine