INTEC   05402
INSTITUTO DE DESARROLLO TECNOLOGICO PARA LA INDUSTRIA QUIMICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
A Molecular Dynamics characterization of the structure and dynamics of the spin label doxyl cholestane in DPPC model membrane in fluid phase
Autor/es:
A. SERGIO GARAY; DANIEL E. RODRIGUES; SOFÍA A. GEGENSCHATZ
Lugar:
Buenos Aires
Reunión:
Congreso; Reunión conjunta de Sociedades de Biociencias, XLVI Reunión anual de la Sociedad Argentina de Biofísica (SAB); 2017
Institución organizadora:
Sociedad Argentina de Biofísica
Resumen:
The sterol 3-beta-Doxyl-5-alpha-Cholestane (DC) is used in Electronic Paramagnetic Resonance spectroscopy (EPR) as a spin label to study the dynamics of biological and model membranes. DC merges into the lipid bilayers due to its structural similarity with the cholesterol molecule, becoming a local sensor of the dynamics of its environment. The EPR spectra are interpreted assuming that the sterol moiety of the DC molecules locates at the hydrophobic region of the membrane and its doxyl ring sites around the polar heads. Nevertheless, there are no additional experimental results that confirm these assumptions. We performed long molecular dynamics simulations (~ 0.8μs) of DC in molar concentrations lower than 0.5%, in Dipalmitoyl PhosPhatidyl Choline (DPPC) membranes at 50oC (fluid phase) to characterize the dynamics of this sterol. The evolution of the systems toward the equilibrium state were followed by analyzing the atomic density depth profiles of the phospholipids and DC atoms in consecutive intervals of simulation time along the trajectory. We observe many events of the DC molecule switching hemi-layer (flip-flop) along the simulated time with a mean time between them of the order of 100ns. This value between flip-flop events is 3 orders of magnitude smaller than those observed for cholesterol in lipid membranes with 30% molar of this sterol. In time intervals between flip-flop events, the doxyl ring moiety of DC distributes mainly at depths among the carbonyl oxygens and the phosphate groups of the phospholipids. From the analysis of the order parameters associated to the orientations of the nitroxide and the sterol rings, we conclude that the orientational dynamics of the normal to the doxyl ring, which determines the EPR spectrum, closely follows that of the sterol rings. The sterol ring moiety locates within the hydrophobic region bellow the deepest carbonyl oxygen of DPPC.