title: Soyacystatin N inhibits proteolysis of wheat alpha-amylase inhibitor and potentiates toxicity against cowpea weevil.
abstract: Genetic engineering may be used to introduce multiple insect resistance genes with different modes of action into crop plants. We explored the possible interactions of two differing gene products fed in the diet of cowpea weevil, Callosobruchus maculates (F.), a stored grain pest. The soybean cysteine protease inhibitor soyacystatin N (scN) and alpha-amylase inhibitor (alphaAI) from wheat have defensive function against this coleopteran. When artificial seeds containing both scN and alpha(AI) were infested with eggs of C. maculatus, the delays in larval development were longer than was predicted by summing the developmental delays seen when larvae were fed a diet containing the individual proteins, indicating that the effects of scN and alpha(AI) are synergistic. Alpha(AI) was readily hydrolyzed when incubated with insect gut extract. This proteolytic degradation was inhibited by scN, but not by Kunitz inhibitor (a serine protease inhibitor). Thus, degradation of alpha(AI) was due to proteolysis by insect digestive cysteine proteases. These data suggest that C. maculatus uses digestive enzymes not only to function in food protein digestion but also to defend the insects themselves by helping reduce the concentration of a toxic dietary protein.
authors.affiliation: Indonesia Agricultural Biotechnology and Genetic Resources Research Institute, Jalan Tentara Pelajar 3A, Bogor 16111, Indonesia.
authors.forename: Bahagiawati
authors.initials: B
authors.lastname: Amirhusin
authors.forename: Richard E
authors.initials: RE
authors.lastname: Shade
authors.forename: Hisashi
authors.initials: H
authors.lastname: Koiwa
authors.forename: Paul M
authors.initials: PM
authors.lastname: Hasegawa
authors.forename: Ray A
authors.initials: RA
authors.lastname: Bressan
authors.forename: Larry L
authors.initials: LL
authors.lastname: Murdock
authors.forename: Keyan
authors.initials: K
authors.lastname: Zhu-Salzman
mesh_terms: D000818:Animals; D015891:Cystatins / Q000494:pharmacology*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004357:Drug Synergism; D010940:Plant Proteins / Q000378:metabolism* / Q000494:pharmacology*; D011480:Protease Inhibitors / Q000494:pharmacology*; D030262:Soybean Proteins; D048889:Weevils / Q000201:enzymology / Q000254:growth & development*
chemical_list: D015891:Cystatins; D010940:Plant Proteins; D011480:Protease Inhibitors; D030262:Soybean Proteins; C060586:WDAI-3 protein, Triticum aestivum; C414109:scN protein, soybean; D003546:Cysteine Endopeptidases