Electronic Paramagnetic Resonance spectra calculated from Molecular Dynamics simulations of pure stearic acid and stearic acid/cholesterol (70:30) bilayers, dopped with 10-doxyl-stearic acid

GARAY, ALBERTO S.; RODRIGUES, DANIEL E.

Rosario, Argentina

Congreso; XXXV Reunión Anual de la Sociedad Argentina de Biofísica; 2006

SAB

The use of Electronic Paramagnetic Resonance (EPR) spectra of spin-labeled-lipids has become an important experimental tool in the study of biological membranes and model bilayers. The analysis and interpretation of the EPR results in these systems are complex and usually based on the use of simplified mathematical models to describe the motion of the spin-label. The aim of this work is to perform a detailed study of the correlation among the spectral features of EPR, and the structure and dynamics of the lipids in which the spin-labeled-molecule is inserted. A generalization of the Steinhoff and Hubbell´s method [Steinhoff H. (1996)] is proposed to obtain the EPR spectra using the spin-label-molecule trajectory obtained from a Molecular Dynamic simulation of the system. First, we study the behavior of the proposed generalization for several angular distributions of the spin-labeled-molecule under conditions of rapid, slow and intermediate label movements. Then, we applied the proposed model to the simulation of the EPR spectra of stearic acid bilayers, and stearic acid-cholesterol compound (70/30) bilayers, doped with 10-doxyl-stearic acid labels at several temperatures (285-330 K). Our results(test) over different angular distribution models showed an interesting point of view of the EPR experiment. In the limit of slow movements, the amplitude of the cone did not affect the spectra obtained. In this regime we always obtained a powder spectra. But in the fast movement limit as the cone amplitude increased the spectra showed more characteristic of a “Marker in solution” behavior. The spectra obtained for each cone with intermediate movements showed to be between their own spectra limits. The apparent order parameters (Sapp) calculated from the spectra is similar to the O.P. of C10 of the labeled molecule. This fact shows that one is able to derive the features of the molecular behavior of the labeled molecule from the spectra. Moreover, the Sapp estimated from the cholesterol simulation was significantly lower than the simulation of pure Stearic Acid indicating that cholesterol diminished the order of the system.