Conformational and binding properties of chicken liver basic fatty acid binding protein in solution

Abstract

The conformation of basic fatty acid binding protein from chicken liver and the binding properties of the apo protein toward 11-dansylamino-undecanoic acid were investigated by CD and fluorescence spectroscopy. In one set of experiments the binding process was followed by the appearance of induced optical activity in the absorption region of the dansyl chromophore. In a second set of experiments the binding process was followed by the large enhancement of emission fluorescence of the dansyl fluorophore. From the saturation curves, the stoichiometry of the complex and the binding constant of the fatty acid to the protein were precisely determined. The values of the dissociation constant determined with the two methods were in excellent agreement: we obtained KD = (1.0 +/- 0.1) x 10(-6) M in a 0.9: 1 stoichiometry. The native conformation of the protein is remarkably stable in a variety of solvent systems, including acetonitrile-water, ethylene glycol-water, and dioxane-water of various compositions. The CD results also showed that the binding of the fatty acid does not induce any appreciable change in the protein conformation. In a mixture of water and 2,2,2-trifluoroethanol 1:9 (v/v), the native conformation collapses and a new ordered structure is formed, characterized by a high amount of alpha-helix.