The isolation and partial characterization of a cystatin class cysteine proteinase inhibitor from soybean seeds and its potential to control digestive proteolysis of insect larvae dependent on cysteine proteinases for digestion
Abstract
Cysteine proteinase activity in the midgut of larval Acanthoscelides obtectus (Common bean weevil) was found to be necessary for normal growth and development of the insect. Inhibition of the cysteine proteinase activity resulted in significantly delayed developmental time and increased mortality. Of 44 species and varieties of legume seeds screened for cysteine proteinase inhibitor activity, soybean seeds were found to be the highest. The specific activity of cysteine proteinase inhibitor activity was found to be highest in the hypocotyl of the soybean seed. A 12,000 dalton proteinaceous cysteine proteinase inhibitor was isolated from Century soybeans seeds, using a series of chromatography columns. The cysteine proteinase inhibitor inhibited papain, ficin, and crude gut extracts of the following insect larvae dependent on cysteine proteinases for digestion: Callosobruchus maculatus (cowpea weevil), Tribolium castaneum (red flour beetle), Epilachna varivestis (Mexican bean beetle), Zabrotes subfaciatus (Mexican bean weevil), and A. obtectus. The cysteine proteinase inhibitor was most effective against papain, ficin, and gut extracts of C. maculatus and T. castaneum. The cysteine proteinase inhibitor did not inhibit bovine trypsin, bovine $\alpha$-chymotrypsin, porcine pepsin, or bromelain. A partial N-terminal amino acid sequence showed that the protein is homologous to two members of the cystatin superfamily of cysteine proteinase inhibitors, namely rice oryzacystatin and chicken egg white cystatin. The inhibitory activity of the protein was similar in strength to two well-characterized cysteine proteinase inhibitors, the low molecular weight inhibitor E-64, and chicken egg white cystatin. The soybean inhibitor was heat-labile, with all inhibitory activity destroyed after heating for 30 minutes at 100$\sp\circ$C.
Degree
Ph.D.
Advisors
Nielsen, Purdue University.
Subject Area
Food science|Entomology
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