Conformational Change in a Single Molecular Species, β₃, of β-Conglycinin in Acidic Ethanol Solution

Abstract

Several physicochemical experiments were done to obtain further information on the conformational changes occurring in β-conglycinin in acidic-ethanol solution, using a single molecular species of this protein, β₃. By far-UV circular dichroism (CD), a transition from β-sheet to α-helical structure was observed upon addition of acidic-ethanol, and the α-helix content was found to reach 76% in 70% ethanol (pH 2). From analyses of near-UV CD and difference absorption spectra, it was found that the tertiary structure of the β₃ species was significantly altered at ethanol concentrations between 10 and 20%. The profiles of binding of 1-anilinonaphthalene-8-sulfonic acid to the β₃ species during acidic-ethanol denaturation were indicative of the existence of intermediate conformers in the molten globule-like denaturation state. By measuring Fourier transform infrared spectra and estimating the Stokes radius by dynamic light scattering, the β₃ molecules were found to aggregate with an increase in ethanol concentration.