title: The molecular structure of a phosphatidylserine bilayer determined by scattering and molecular dynamics simulations.
abstract: Phosphatidylserine (PS) lipids play essential roles in biological processes, including enzyme activation and apoptosis. We report on the molecular structure and atomic scale interactions of a fluid bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS). A scattering density profile model, aided by molecular dynamics (MD) simulations, was developed to jointly refine different contrast small-angle neutron and X-ray scattering data, which yielded a lipid area of 62.7 Å(2) at 25 °C. MD simulations with POPS lipid area constrained at different values were also performed using all-atom and aliphatic united-atom models. The optimal simulated bilayer was obtained using a model-free comparison approach. Examination of the simulated bilayer, which agrees best with the experimental scattering data, reveals a preferential interaction between Na(+) ions and the terminal serine and phosphate moieties. Long-range inter-lipid interactions were identified, primarily between the positively charged ammonium, and the negatively charged carboxylic and phosphate oxygens. The area compressibility modulus KA of the POPS bilayer was derived by quantifying lipid area as a function of surface tension from area-constrained MD simulations. It was found that POPS bilayers possess a much larger KA than that of neutral phosphatidylcholine lipid bilayers. We propose that the unique molecular features of POPS bilayers may play an important role in certain physiological functions.
authors.affiliation: Department of Physics, University of South Florida, Tampa, FL 33620, USA. panj@usf.edu.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Pan
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Cheng
authors.forename: Luca
authors.initials: L
authors.lastname: Monticelli
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Heberle
authors.forename: Norbert
authors.initials: N
authors.lastname: Kučerka
authors.forename: D Peter
authors.initials: DP
authors.lastname: Tieleman
authors.forename: John
authors.initials: J
authors.lastname: Katsaras
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D033363:Neutron Diffraction; D010718:Phosphatidylserines / Q000737:chemistry*; D053838:Scattering, Small Angle; D012964:Sodium / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D007477:Ions; D008051:Lipid Bilayers; D010718:Phosphatidylserines; D014867:Water; C050294:1-palmitoyl-2-oleoylglycero-3-phosphoserine; D012964:Sodium; D017666:Deuterium Oxide