Influence of the atomic charges assignment in molecular dynamics simulation of model phospholipid bilayers: a conformational study of the polar heads toward a MD with varying atomic charges

GARAY, ALBERTO S.; NICASTRO, ALCIDES; RODRIGUES, DANIEL E.

Buzios, Río de Janeiro, Brasil

Congreso; Biophysics 2009, VII Congreso Iberoamericano de Biofísica; 2009

Sociedad de Biofísica de Brasil y Argentina, IUPAB

Based on a Molecular Dynamics (MD) simulation of the liquid crystalline phase of a fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer, we performed a cross correlation statistical analysis of the dihedral conformations adopted by the lipid polar heads. We determined the most populated conformations that have lifetimes of the order of 1ns. We assign point atomic charges for each of these conformations by fitting the electric potential to quantum mechanical calculations. The atomic charges assignments obtained are in agreement with other force field parameters obtained by fitting hydration free energies of small esther compounds. We performed new MD simulations using each of the atomic charges assignments obtained for different conformations of the polar head to analyze the relevance of their differences for the MD results. The simulations were performed in the ensemble of constant surface tension (g) and the values of g were adjusted to fit the experimental Deuterion order parameter profiles. The results show that atomic charge differences as small as 0.1|e| among the carbonyl oxygens of the acyl chains are enough to shift the atomic density profiles peaks of these moieties by ~1 Å. Also the hydration level of the different polar moieties of the head are affected by the various charge assignments corresponding to different conformations. Based on this study we propose a MD simulation algorithm that implements atomic charge temporal variation for each lipid that follows the conformational changes in the polar head.