Acidic residue modifications restore chaperone activity of beta-casein interacting with lysozyme
An important factor in medicine and related industries is the use of chaperones to reduce protein aggregation. Here we show that chaperone ability is induced in beta-casein by modification of its acidic residues using Woodward's Reagent K (WRK). Lysozyme at pH 7.2 was used as a target protein to study beta-casein chaperone activities. The mechanism for chaperone activity of the modified beta-casein was determined using UV-vis absorbencies, fluorescence spectroscopy, differential scanning calorimetry and theoretical calculations. Our results indicated that the beta-casein destabilizes the lysozyme and increases its aggregation rate. However, WRK-ring sulfonate anion modifications enhanced the hydrophobicity of beta-casein resulting in its altered net negative charge upon interactions with lysozyme. The reversible stability of lysozyme increased in the presence of WRK-modified beta-casein, and hence its aggregation rate decreased. These results demonstrate the enhanced chaperone activity of modified beta-casein and its protective effects on lysozyme refolding. (C) 2011 Elsevier B.V. All rights reserved.