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Cholesterol Surrogates: A Comparison of Cholesterol and 16:0 Ceramide in POPC Bilayers

Sagar A. Pandit ^*, See-Wing Chiu , Eric Jakobsson , Ananth Grama ^* and H. L. Scott 

^* Department of Computer Science, Purdue University, West Lafayette, Indiana; Department of Molecular and Integrative Physiology, Department of Biochemistry, UIUC Programs in Biophysics, Neuroscience, and Bioengineering, National Center for Supercomputing Applications, and Beckman Institute, University of Illinois, Urbana, Illinois; and Department of Biological, Chemical, and Physical Sciences, Illinois Institute of Technology, Chicago, Illinois

Correspondence: Address reprint requests to H. L. Scott Jr., Tel.: 312-567-3730; E-mail: scotth{at}iit.edu.

Experimental evidence indicates that, under some circumstances, "surrogate" molecules may play the same role as cholesterol in ordering membrane lipids. The simplest molecule in this class is Ceramide. In this article, we describe atomic-level molecular dynamics simulations designed to shed light on this phenomenon. We run simulations of hydrated phosphoryl-oleoyl phosphatidylcholine (POPC) bilayers containing cholesterol, and containing ceramide, in concentrations ranging from 5% to 33%. We also perform a simulation of a pure POPC bilayer to verify the simulation force fields against experimental structural data for POPC. Our simulation data are in good agreement with experimental data for the partial molecular volumes, areas, form factors, and order parameters. These simulations suggest that ceramide and cholesterol have a very similar effect on the POPC bilayer, although ceramide is less effective in inducing order in the bilayer compared with cholesterol at the same concentrations.