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 (alpha M-2). alpha M-2 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-alpha M-2 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 alpha M-2-tannic acid complex. The thermodynamic signatures of this interaction reveals hydrogen bonding played a major role in the binding of alpha M-2-tannic acid. Analysis of CD and FTIR results suggest a minor conformational change in alpha M-2 on tannic acid binding. Overall, tannic acid induces subtle conformation change in alpha M-2 structure resulting the loss of its proteinase inhibitory activity. (C) 2018 Published by Elsevier B.V.