A Kunitz-type serine protease inhibitor from Butea monosperma seed and its influence on developmental physiology of Helicoverpa armigera

Abstract

A protease inhibitor from the seeds of Butea monosperma (BmPI) was purified, characterized and studied for its influence on developmental physiology of Helicoverpa armigera. BmPI on two-dimensional separations indicated the presence of a 14kDa protein with an isoelectric point in the acidic region (pI 5.6). Multiple Sequence Analysis data suggested that the BmPI contains a sequence motif which is conserved in various trypsin and chymotrypsin inhibitors of Kunitz-type. The inhibitor exhibited trypsin inhibitory activity in a broad range of pH (4–10) and temperature (10–80°C). The enzyme kinetic studies revealed BmPI as a competitive inhibitor with a Ki value of 1.2×10−9M.In vitro studies with BmPI indicated measurable inhibitory activity on total gut proteolytic enzymes of H. armigera (IC50 2.0μg/ml) and bovine trypsin. BmPI supplemented artificial diet caused dose dependent mortality and reduction in growth and weight. The fertility and fecundity of H. armigera, declined whereas the larval–pupal duration of the insect life cycle extended. These detrimental effects on H. armigera suggest the usefulness of BmPI in insect pest management of food crops.