Abstract
Tea flavonoids bind to variety of enzymes and inhibit their activities. In the present study, binding and inhibition of catalase activity by catechins with respect to their structure-affinity relationship has been elucidated. Fluorimetrically determined binding constants for (−)-epigallocatechin gallate (EGCG) and (−)-epicatechin gallate (ECG) with catalase were observed to be 2.27×106 M−1 and 1.66×106 M−1, respectively. Thermodynamic parameters evidence exothermic and spontaneous interaction between catechins and catalase. Major forces of interaction are suggested to be through hydrogen bonding along with electrostatic contributions and conformational changes. Distinct loss of α-helical structure of catalase by interaction with EGCG was captured in circular dichroism (CD) spectra. Gallated catechins demonstrated higher binding constants and inhibition efficacy than non-gallated catechins. EGCG exhibited maximum inhibition of pure catalase. It also inhibited cellular catalase in K562 cancer cells with significant increase in cellular ROS and suppression of cell viability (IC50 54.5 µM). These results decipher the molecular mechanism by which tea catechins interact with catalase and highlight the potential of gallated catechin like EGCG as an anticancer drug. EGCG may have other non-specific targets in the cell, but its anticancer property is mainly defined by ROS accumulation due to catalase inhibition.
Highlights
Green tea polyphenols have received wide attention for their beneficial health effects
Isothermal titration calorimetry (ITC) can reveal the stoichiometry, enthalpy free energy, and entropy changes that occur over the course of a reaction [45,46]
Data obtained from the titration are presented by the series of peaks corresponding to each injection
Summary
Green tea polyphenols have received wide attention for their beneficial health effects. The major anticancer activities of tea catechins are as antioxidants, pro-oxidants and enzyme inhibitors [4,5,6,7,8]. Antioxidant activity of tea polyphenols has found wide application in radioprotection and chemoprevention by scavenging reactive oxygen species (ROS) [9,10,11,12,13]. Galloylated catechins, especially EGCG, are known to inhibit growth of cancer cells and induce apoptosis in various types of tumor cells due to their pro-oxidant activity [14,15,16,17]. Various mechanisms may be associated with the pro-oxidant behavior of flavonoids in cancer cells, of which enzyme inhibition is a major process
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