Coarse-Grain
Simulations of Skin Ceramide NS with Newly Derived Parameters Clarify Structure
of Melted Phase
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Abstract
Ceramides are lipids that are involved
in numerous biologically
important structures (e.g., the stratum corneum and ceramide-rich
platforms) and processes (e.g., signal transduction and membrane fusion),
but their behavior is not fully understood. We report coarse-grain
force field parameters for <i>N</i>-lignocerylsphingosine
(ceramide NS, also known as ceramide 2) that are consistent with the
Martini force field. These parameters were optimized for simulations
in the gel phase and validated against atomistic simulations. Coarse-grained
simulations with our parameters provide areas per lipid, membrane
thicknesses, and electron density profiles that are in good agreement
with atomistic simulations. Properties of the simulated membranes
are compared with available experimental data. The obtained parameters
were used to model the phase behavior of ceramide NS as a function
of temperature and hydration. At low water content and above the main
phase transition temperature, the bilayer melts into an irregular
phase, which may correspond to the unstructured melted-chain phase
observed in X-ray diffraction experiments. The developed parameters
also reproduce the extended conformation of ceramide, which may occur
in the stratum corneum. The parameters presented herein will facilitate
studies on important complex functional structures such as the uppermost
layer of the skin and ceramide-rich platforms in phospholipid membranes