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

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.