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

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 ß-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.

Binding interaction of sheep alpha-2-macroglobulin and tannic acid: A spectroscopic and thermodynamic study.

Tannic acid is a polyphenol found in plant species commonly consumed by ruminants. It works as an important molecule in plant defense system to fight against environmental stressors. Tannic acid has number of effects on animals and humans. An attempt has been made to study the interaction of tannic acid with alpha-2-macroglobulin (α2M). α2M is a large tetrameric glycoprotein which function as a key serum anti-proteinase under physiological conditions. In the present study we explored the tannic acid-α2M interaction by number of spectroscopic techniques such as UV, fluorescence, CD and FTIR along with isothermal titration calorimetry. CD and FT-IR spectroscopy were mainly used to study the secondary structural change induced in the antiproteinase. Analysis of activity shows the antiproteolytic potential of protein was compromised. Data of UV spectroscopy shows formation of α2M-tannic acid complex. The thermodynamic signatures of this interaction reveals hydrogen bonding played a major role in the binding of α2M-tannic acid. Analysis of CD and FTIR results suggest a minor conformational change in α2M on tannic acid binding. Overall, tannic acid induces subtle conformation change in α2M structure resulting the loss of its proteinase inhibitory activity.