INVESTIGADORES
RODRIGUES Daniel Enrique
congresos y reuniones científicas
Título:
Study of the behavior of a N-doxyl spin label in a model lipid bilayer in gel-like phases by Molecular Dynamics: Structural and dynamic properties and EPR spectra calculations
Autor/es:
VARTORELLI, MARTIN R.; GARAY, ALBERTO S.; RODRIGUES, DANIEL E.
Lugar:
Montevideo, Uruguay
Reunión:
Congreso; XXXVI Reunión Anual de la Sociedad Argentina de Biofísica, 6th International Conference on Biological Physics y 5th Southern Cone Biophysics Congress; 2007
Institución organizadora:
IUPAP, IUPAB, SAB, SUB
Resumen:
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We
have performed Molecular Dynamics simulations of Stearic Acid (SA)
bilayers in water to study how the insertion of a N-doxyl labeled SA
affects the structure of the lipid assembly and how it senses the
dynamic of the host system. The simulations were carried out at the
NPZ<gama>T ensemble and several values of <gama> are
scanned. The host system present a phase transition between two
ordered phases at <gama>=1900 bar.nm for T=27°C (and
<gama>=1850 for T=42°C). The analysis of the
Structure Factor of the surface shows that the transition occurs
between a 2D hexagonal phase with tilt-angle toward NN, and an
oblique lattice phase with larger tilting toward the NN neighbors and
areas. The axial autocorrelation functions of the acyl chains have
correlation times typical of a free rotator phase in both cases. To
evaluate the doxyl-labeled effects, the 5D-SA, 12D-SA and 16D-SA, the
most popular labels used in EPR experiments are inserted in the host
systems. At the spin-label concentration used in this work (1:280)
the lipid host systems are only perturbed in the first neighbor shell
closest to the doxyl. An important result of these simulations is the
average positions where spin-labeled at different sites lie. Our
results show a picture very different from the naive vision of a
doxyl ring positioned at the depth of the Cn of the alkyl chains of
the host system. Only 12D-SA presents configurations where the doxyl
ring remains in the middel of each layer. Conversely 5D-SA migrates
to the water-lipid interface, and 16D-SA toward the center of the
bilayer. These facts lead to different mechanism by the which the
spin-label senses the dynamics of the host system. Also there are
other variables that affect the properties surveyed by the EPR
spectra.