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Identification of a New Soybean Kunitz Trypsin Inhibitor Mutation and Its Effect on Bowman−Birk Protease Inhibitor Content in Soybean Seed

Jason D. Gillman, Won-Seok Kim, Hari B. Krishnan
Journal of agricultural and food chemistry 2015 v.63 no.5 pp. 1352-1359
Kunitz-type proteinase inhibitor, weight gain, polyacrylamide gel electrophoresis, antibodies, chymotrypsin, energy, essential amino acids, feed meals, gene overexpression, germplasm, heat treatment, homozygosity, mutants, mutation, proteome, seeds, soy protein, soybean meal, soybeans, trypsin
Soybean seed contains antinutritional compounds that inactivate digestive proteases, principally corresponding to two families: Kunitz trypsin inhibitors (KTi) and Bowman–Birk inhibitors (BBI). High levels of raw soybean/soybean meal in feed mixtures can cause poor weight gain and pancreatic abnormalities via inactivation of trypsin/chymotrypsin enzymes. Soybean protein meal is routinely heat-treated to inactivate inhibitors, a practice that is energy-intensive and costly and can degrade certain essential amino acids. In this work, we screened seed from 520 soybean accessions, using a combination of sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) and immunoblots with anti-Kunitz trypsin inhibitor antibodies. A soybean germplasm accession was identified with a mutation affecting an isoform annotated as nonfunctional (KTi1), which was determined to be synergistic with a previously identified mutation (KTi3–). We observed significant proteome rebalancing in all KTi mutant lines, resulting in dramatically increased BBI protein levels.