Comparison of the properties of Gel and Liquid Crystalline phases of DPPC through molecular dynamic simulation of an unified atomistic model

DANIEL E. RODRIGUES; A. SERGIO GARAY; FERNANDO SILVERA

Salta

Congreso; 3rd.Latinamerican Protein Society Meeting-XXXIX Biophysical Soc. Meeting; 2010

SAB y Sociedad Latinoamericana de Proteinas

Molecular Dynamic (MD) simulations of hydrated phospholipid bilayers have probed to be important to understand the properties of biomembranes and their interactions with water. The Liquid Crystalline (LC) phase of DPPC has been among the most studied systems due to its claimed biological relevance. The more compact phases that appear at low temperature (e.g. Gel) have been less studied by MD partially because they were considered not biologically relevant, but also because it is difficult to obtain equilibrated systems starting from crystalline structures. The relevance acquired by compact lipid domains in biomembranes claims for a deeper understanding of this model phases. We present here MD-simulations of hydrated DPPC bilayers of 480 lipids at 50°C (LC) and 22°C (Gel) using the same forcefield and ensemble. At variance with previous works the Gel phase is obtained from the LC structure to avoid being trapped in local minima of the crystal structure during the equilibration stage. We start fitting only the surface tension parameter to obtain order parameter profiles at 50°C in agreement with experiments. No further parameter modification is performed when changing the temperature and therefore the calculated properties can be meaningfully contrasted with experimental information. The calculated structure factor shows that Gel-phase orders in a two dimensional oblique lattice and the acyl chains are tilted 30.4° , conversely the LC-phase does not show orientational order. The area/lipid are 46.6A² (Gel) and 61.2A² (LC). The dihedral-angle- , acylic-plane-orientational- and tilt distributions are compared between phases along with rotational correlation times.