Molecular Structure of Sphingomyelin in Fluid Phase Bilayers Determined by the Joint Analysis of Small-Angle Neutron and X-ray Scattering Data

• DOI: 10.1021/acs.jpcb.0c03389
• Publication Date: 2020-05-29T10:13:50Z
• Authors: Milka Doktorova; Norbert Kučerka; Jacob J. Kinnun; Jianjun Pan; Drew Marquardt; Haden L. Scott; Richard M. Venable; Richard W. Pastor; Stephen R. Wassall; John Katsaras; Frederick A. Heberle
• Keywords: Force Field; Densitometry

We have determined the fluid bilayer structure of palmitoyl sphingomyelin (PSM) and stearoyl (SSM) by simultaneously analyzing small-angle neutron X-ray scattering data. Using a newly developed density profile (SDP) model for lipids, we report structural parameters including area per lipid, total thickness, hydrocarbon in addition to lipid volumes densitometry. Unconstrained all-atom simulations PSM bilayers at 55 °C using C36 CHARMM force field produced 56 Å2, value that is 10% lower than one experimentally SDP analysis (61.9 Å2). Furthermore, form factors calculated from unconstrained were poor agreement with experimental factors, even though segmental order parameter (SCD) profiles relatively good SCD obtained NMR experiments. Conversely, constrained 61.9 Å2 resulted between simulation but not NMR. discuss possible reasons discrepancies these two types data are frequently used as validation metrics molecular dynamics fields.