Identification of an a-Amylase inhibitor from pterodon pubescens with ability to inhibit cowpea weevil digestive enzymes

Cowpea seeds (Vigna ungiculata) are widely cultivated by poor farmers in Latin America and Africa and are often severely damaged by the cowpea weevil Callosobruchus maculatus. A proteinaceous inhibitor of cowpea weevil digestive enzymes, PpAI, was purified from white sucupira seeds (Pterodon pubescens) and biochemically characterized in this study. Proteins were extracted from seeds and precipitated with ammonium sulfate at 100% saturation. This fraction was applied onto a Redsepharose CL-6B column, and the retained peak showed 70% inhibitory activity toward larval C. maculatus digestive R-amylases. The retained peak was then purified using an analytical reversedphase HPLC column. Purified PpAI showed 65% inhibitory activity against larval C. maculatus enzymes. Enzymatic assays also showed that the purified P. pubescens inhibitor was unable to reduce the activity of mammalian R-amylases, suggesting specificity toward insect enzymes. Moreover, artificial seeds containing PpAI were able to reduce larval weight by 36% and cause 55% mortality. Mass spectrometry and SDS-PAGE analyses indicated that PpAI showed a molecular mass of approximately 5.0 kDa. This R-amylase inhibitor, coming from a native Cerrado plant, could be used to construct a genetically engineered cowpea with enhanced resistance against weevil pests