Oxadiargyl induced conformational transition of cystatin isolated from yellow mustard seeds: Biophysical and biochemical approach

Phytocystatins are thiol proteinase inhibitors crucial due to their inhibitory activity in plants. These play important roles in improving crop yield, protection against insects and pathogens and modulation of apoptosis. In this chemical era, various pesticides are being used globally to increase the crop biomass. These pesticides accumulate in plant body and produce harmful effects on plants itself by interacting with essential proteins. In this present study, we have monitored the interaction of a herbicide; oxadiargyl, with phytocystatin isolated from yellow mustard seeds (YMP) by employing spectroscopic techniques viz. UV, fluorescence, FTIR and CD spectroscopy and Isothermal titration calorimetry (ITC). UV and fluorescence spectroscopy shows YMP transformation from native to non-native form apparent by decreased absorbance and decreased fluorescence. FTIR and CD spectroscopy further confirmed secondary structural disruption of YMP. Anti-papain activity assay was also carried out; a reduction in activity was observed in presence of oxadiargyl. Thermodynamic parameters obtained from ITC and stern-volmer plot shows affinity of oxadiargyl towards phytocystatin. Oxadiargyl was also found to induce ROS generation in YMP as evident by DNPH assay. Thus oxadiargyl binds to phytocystatin causing structural alterations reducing its physiological benefits and altering its functionality and ultimately leading to reduced crop yield.