soybean trypsin inhibitor (STI)-like domain, beta-trefoil fold, found in Psophocarpus tetragonolobus chymotrypsin inhibitor 3 (WCI-3) and similar proteins
This subfamily includes Psophocarpus tetragonolobus WCI-3, trypsin inhibitor 1 (WTI-1), and trypsin inhibitor DE-3 from Erythrina caffra (ETI). WTI-1 is a Kunitz type protease inhibitor that inhibits bovine trypsin stoichiometrically, but not bovine alpha-chymotrypsin. WCI-3 is a Kunitz-type winged bean chymotrypsin inhibitor (WbCI) that inhibits alpha-chymotrypsin at the molar ratio of 1:2 instead of 1:1, the usual ratio of 1:1 common to other members of the family. ETI is a trypsin inhibitor that shows high homology to other Kunitz trypsin protease inhibitors, but has the unique ability to bind and inhibit tissue plasminogen activator. Members of this subfamily contain an STI-like domain with a beta-trefoil fold, which is characterized by 12 beta strands folded into three similar trefoil subdomains (alpha, beta, and gamma) associated to give an overall structure with pseudo-3-fold symmetry.
Jiyao W et al.(2023). "The conserved domain database in 2023.",