Soybean trypsin inhibitor (STI)

Soybean trypsin inhibitors (STIs) are a group of proteins found in the seeds of the soybean plant (Glycine max) that function as potent inhibitors of serine proteases, specifically trypsin and chymotrypsin [1.3.1, 1.5.1]. The two primary types are the Kunitz trypsin inhibitor (KTI), which is a ~21 kDa protein that primarily targets trypsin, and the Bowman-Birk inhibitor (BBI), a ~8 kDa protein with distinct binding sites for both trypsin and chymotrypsin [1.4.1, 1.5.1]. Biologically, these inhibitors serve as a defense mechanism for the plant against herbivorous insects by disrupting their digestive processes [1.5.1]. While traditionally classified as anti-nutritional factors due to their ability to impair protein digestion and induce pancreatic hypertrophy in animal models, STIs have demonstrated significant therapeutic potential [1.1.2, 1.3.5]. Bowman-Birk Inhibitor Concentrate (BBIC) has been extensively studied in clinical trials for its chemopreventive properties against various cancers and its anti-inflammatory effects in conditions such as ulcerative colitis [1.1.2, 1.4.1]. Additionally, recent research suggests that STIs may inhibit viral entry, including SARS-CoV-2, by blocking host cell surface proteases like TMPRSS2 [1.1.3, 1.2.1]. Despite these benefits, safety concerns remain regarding their anti-nutritional effects and potential to cause pancreatic changes upon chronic high-level exposure [1.3.5].

Other names

Kunitz trypsin inhibitorBowman-Birk inhibitorSBTISKTIBBTITrypsin inhibitor A

Soybean trypsin inhibitors act as competitive, reversible inhibitors of serine proteases, such as trypsin and chymotrypsin. They form stable, stoichiometric, enzymatically inactive complexes with the active sites of these enzymes, thereby preventing the cleavage of substrate proteins [1.5.1, 1.3.5].