Insights into ligand binding to a glutathione S-transferase from mango: Structure, thermodynamics and kinetics

We studied a mango glutathione S-transferase (GST) (Mangifera indica) bound to glutathione (GSH) and S-hexyl glutathione (GSX). This GST Tau class (MiGSTU) had a molecular mass of 25.5 kDa. MiGSTU Michaelis-Menten kinetic constants were determined for their substrates obtaining a Km, Vmax and kcat for CDNB of 0.792 mM, 80.58 mM min−1 and 68.49 s−1 respectively and 0.693 mM, 105.32 mM min−1 and 89.57 s−1, for reduced GSH respectively. MiGSTU had a micromolar affinity towards GSH (5.2 μM) or GSX (7.8 μM). The crystal structure of the MiGSTU in apo or bound to GSH or GSX generated a model that explains the thermodynamic signatures of binding and showed the importance of enthalpic-entropic compensation in ligand binding to Tau-class GST enzymes. •Plant Tau-class of GST enzymes are less understood compared to their mammalian counterparts.•Enzymatic, thermodynamic and crystallographic studies of mango Tau GST are presented.•Binding of GSH is mediated by enthalpic effects and hydrogen bonds to the G-site.•Alkylated GSH analogues like GSX is tightly bound by entropic compensation and hydrophobic interactions to the H-site.•Overall the calorimetric and crystallographic data explain the conformational changes that led to an efficient enzyme that bind and process xenobiotics.