Theoretical studies of membranes at different thermotropic phases in salts solutions by molecular dynamics

FERNANDO E. HERRERA; M. MILAGROS SALES; DANIEL E. RODRIGUES

Oro Verde, Entre Ríos

Congreso; 3er. Congreso de Bioinformática y Biología Computacional; 2012

Asociación Argentina de Bioinformática y Biología Computacional

Biological membranes are very complex systems since their structure and dynamic characteristics are affected by different conditions such as temperature or the ionic composition of aqueous buffers around them. The temperature determines the thermotropic phases and ordering of the lipids, like the ordered Gel (G) or the Liquid crystalline (LC). The ionic concentration on the other hand affects the membrane fluidity. Therefore, theoretical studies of the interplay between these two factors are necessary to understand the molecular mechanisms of their interactions. Molecular dynamics have proven to be a reliable tool to study biomembranes in detail. In this context, we have performed Molecular Dynamics simulations of DPPC (Dipalmitoylphosphatidylcholine) hydrated bilayers at Gel (T=22°C) and Liquid Crystalline (T=50°C) phases, at different ionic concentration of NaCl in order to rationalize the effect of the ionic forces on different thermotropic phases of the same system. In this work, we have developed several tools to analyze in detail the structural and dynamical properties affected by the ionic concentration (area per lipid, atomic density profiles, thickness fluctuations 2Dmaps, ion depth profiles, ion solvation depth profiles, diffusion coefficients, etc).The results, that are in agreement with previous reports, show that the ionic absorption and the effects of the ions on many membrane properties depend primarily on the phase of the membranes. The area per lipid and the diffusion coefficients in the LC phase is reduced when the ionic concentration increase while they remain unchanged in G phase. Additionally, it was found that the bilayer thickness in LC phase increase with the salt concentration. Furthermore, the absorbed Na ions interact principally with the carbonyl oxigens in both phases (see Figure 1). This work has finally contributed to emphasize that salt concentration and temperature are important factors to take into account in the design of any kind of experiments.