Conformational changes of β-lactoglobulin in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles -: A fluorescence and CD study

The effect of beta-lactoglobulin encapsulation in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles on the environment of protein and on Trp was analysed at different water contents (omega(0)). CD data underlined the distortion of the beta-sheet and a less constrained tertiary structure as the omega(0) increased, in agreement with a concomitant red shift and a decrease in the signal intensity obtained in steady-state fluorescence measurements. Fluorescence lifetimes, evaluated by biexponential analysis, were tau(1) = 1.28 ns and tau(2) = 3.36 ns in neutral water. In reverse micelles, decay-associated spectra indicated the occurrence of important environmental changes associated with omega(0). Bimolecular fluorescence quenching by CCl4 and acrylamide was employed to analyse alterations in the accessibility of the two Trp residues in beta-lactoglobulin, induced by changes in omega(0). The average bimolecular quenching constant increases with omega(0). The drastic decrease with omega(0) of k(q), associated with the longest lifetime, k(q2)(CCl4), comparatively to the increase of > k(q2)(acrylamide) (water) also confirms the important conformational changes of encapsulated beta-lactoglobulin.