Estudo estrutural de membranas modelo que contem proteinas extrinsecas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1979

RESUMO

Protein free lipid bilayers have been intensely studied during the past few years due to the striking similarities between these systems and natural membranes. In recent years, with the purpose of attaining a better simulation with the natural systems, proteins have been incorporated into the bi1ayers. It is a fact that the location and tributiori of the protein in the plane of the membrane has not been completely determined for a number of membrane systems. Extrinsec proteins, like cytochrome C, seem to be superficially bound to the membrane by electrostatic forces and remain a1most completely on the aqueous side defined by the polar groups of the lipids (11, 15). More recently been proposed that extrinsec proteins might also have some hidrofobic interaction with the lipid hydrocarbon chains or even with the intrinsec proteins. Furthermore, the existence of some seem to indicate a slight penetration of Cyt.C in the 1ipid bilayes (18,28), have motivated the structural work undertaken by us. Preparation of X-ray samples of three phospholipid systems was done following the usual techniques. Low angle X-ray diffraction diagrams were obtained for wet rnultilayers of Dipalmitoyl Phosphatidyl Choline (DPL), Cardiolipin / DPL (1 : 4) and Cardiolipin / DPL / Cytochrome C. (5 : 20 : 1). The molar ratios here specified proved to be the ones that produced better diffraction patterns. Analysis of the lamellar diffraction using one of the usual phasing techniques for this kind of problem, allowed us to obtain the electron density profile of the model membrane systems under study, with a resolution of approximately 5 A. A close examination of the electron density profiles showed some perturbation in the membrane surface region upon introduction of the Cytochrome C. The hydrofobic central region seemed to remain practically unaltered. Both these results agree with the outcome of recent NMR and EPR experiments(18). A model proposed for the DPL / Card / Cyt C membrane is confirmed by our experiments.

ASSUNTO(S)

biologia molecular biofisica

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