Inhibitory specificity and insecticidal selectivity of α-amylase inhibitor from Phaseolus vulgaris

Abstract

The primary structure and proteolytic processing of the α-amylase isoinhibitor α AI-1 from common bean ( Phaseolus vulgaris cv. Magna) was determined by protein chemistry techniques. The inhibitory specificity of αAI-1 was screened with a panel of the digestive α-amylases from 30 species of insects, mites, gastropod, annelid worm, nematode and fungal phytopathogens with a focus on agricultural pests and important model species. This in vitro analysis showed a selective inhibition of α-amylases from three orders of insect (Coleoptera, Hymenoptera and Diptera) and an inhibition of α-amylases of the annelid worm. The inhibitory potential of αAI-1 against several α-amylases was found to be modulated by pH. To understand how αAI-1 discriminates among closely related α-amylases, the sequences of the α-amylases sensitive, respectively, insensitive to αAI-1 were compared, and the critical determinants were localized on the spatial α-amylase model. Based on the in vitro analysis of the inhibitory specificity of αAI-1, the in vivo activity of the ingested αAI-1 was demonstrated by suppression of the development of the insect larvae that expressed the sensitive digestive α-amylases. The first comprehensive mapping of αAI-1 specificity significantly broadens the spectrum of targets that can be regulated by α-amylase inhibitors of plant origin, and points to potential application of these protein insecticides in plant biotechnologies.