Biophysical analysis of interaction between curcumin and alpha-2-macroglobulin.

Alpha-2-macroglobulin (αM) is large glycoprotein present in the body fluids of vertebrates. It is an antiproteinase that inhibits a broad spectrum of proteases without the direct blockage of the protease active site. Curcumin, a yellow spice commonly used in India and several Asian countries, is reported to have anti-tumor and anti-inflammatory effects because of its antioxidant properties. In the present study, we have explored the interaction of curcumin with αM using various technique such as antiproteinase activity assay, spectroscopy. Changes in the secondary structure of αM following interaction with curcumin was investigated by CD and FT-IR spectroscopy. Thermodynamics of curcumin-αM binding were also analyzed by isothermal titration calorimetry to identify the number of binding sites, changes in enthalpy, entropy and Gibbs free energy changes for this interaction. Thermodynamics parameters reveal that the binding is exothermic in nature. Our results suggest that the binding of curcumin with αM induces a conformational change in the native form of protein that compromises its anti-proteinase activity. This exothermic and spontaneous interaction leads to alteration in the β-sheet content of the protein leading to subtle changes in conformational status of the protein leading possibly to loss in the antiproteinase potential of the inhibitor.