Activity of α-amylase inhibitors from Phaseolus coccineus on digestive α-amylases of the coffee berry borer

Seeds of scarlet runner bean (Phaseolus coccineus L.) were analyzed for alpha-amylase inhibitor (alpha-AI) activity. By using polyclonal antibodies raised against pure alpha-AI-1 from common bean (Phaseolus vulgaris L.), we detected the typical alpha-AI polypeptides (Mr 14 -18 kDa) as well as a large polypeptide of Mr 32,000 Da, usually referred to as amylase inhibitor like. We examined the inhibitor activity present in four accessions of P. coccineus, both in semiquantitative zymograms allowing the separation of different isoforms and in quantitative assays against human salivary amylase, porcine pancreatic amylase and coffee berry borer, Hypothenemus hampei Ferrari (Coleoptera: Scolytidae), amylase. Differential inhibition curves lead us to suggest that the gene encoding one of the inhibitors in P. coccineus (in accession G35590) would be a good candidate for genetic engineering of coffee resistance towards the coffee berry borer. An in vitro proteolytic digestion treatment of pure alpha-AI resulted in a rapid loss of the inhibitory activity, seriously affecting its natural capacity to interact with mammalian alpha-amylases.