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

Abstract

Alpha-2-macroglobulin (α₂M) 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 α₂M using various technique such as antiproteinase activity assay, spectroscopy. Changes in the secondary structure of α₂M following interaction with curcumin was investigated by CD and FT-IR spectroscopy. Thermodynamics of curcumin-α₂M 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 α₂M 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.

Keywords: Alpha-2-macroglobulin; Antiproteinase activity; Circular dichroism; Curcumin; Fourier transform infrared spectroscopy.