Calorimetric and Spectroscopic investigations β-lactoglobulin upon interaction with copper ion

The effect of copper(II) ions (Cu+2) on the structure of beta-lactoglobulin (beta-lg) was investigated spectroscopically using UV-visible, fluorescence and circular dichroism (CD) and calorimetrically using isothermal titration calorimetry (ITC), at different temperatures. Results of the UV-visible studies showed that adding Cu+2 to beta-lg solution caused increasing turbidity, indicative of protein aggregation. It was noticeable that the rate of increasing turbidity was directly proportional to increasing temperature. The far-UV CD studies displayed that the Cu+2 cannot induce any significant changes in the secondary structures of beta-lg at different temperatures. Also, the ITC data indicated that the binding process of Cu+2 to beta-lg is mainly entropically driven. The results highlight that copper ions cause the tertiary structure of beta-lg to change and induce a slightly open structure leading to the formation of supramolecular aggregates in beta-lg which may result in the reduced allergenicity of beta-lg and its increased use in industrial applications.