Structure of the Kunitz-Type Soybean Trypsin Inhibitor (STI): Implication for the Interactions Between Members of the STI Family and Tissue-Plasminogen Activator

Abstract

The Kunitz-type soybean trypsin inhibitor (STI) has played a key role in the early study of proteinases, having been used as the main substrate in the biochemical and kinetic work that led to the de®nition of the standard mechanism of action of proteinase inhibitors. A partial structure of STI complexed with porcine trypsin has previously been reported, in which the ®rst 93 residues of the inhibitor, including the region of contact with trypsin, were relatively well de®ned, whereas for the remaining part of the peptide chain only some C atoms were located. The structure of the inhibitor in its free form has now been determined by molecular replacement to 2.5 A Ê , using the coordinates of the homologous Erythrina trypsin inhibitor as a search model. When the re®ned atomic coordinates of STI are compared with the partial model previously available, the conformation of the reactive-site loop and its position with respect to the main body of the molecule does not change when the inhibitor interacts with trypsin. There are instead, despite the high similarity in the overall tertiary structure, signi®cant differences between STI and Erythrina trypsin inhibitor (ETI) in the region which is in contact with the enzyme in the STI:trypsin crystal structure. Some of these differences can explain the unique speci®city of ETI and its ability to inhibit the ®brinolytic enzyme tissue-type plasminogen activator.

Changes in gene expression during germination reveal pea genotypes with either “quiescence” or “escape” mechanisms of waterlogging tolerance

“…The downregulation of UDP‐glucosyltransferase might have negative effect on seed germination in sensitive BM‐3 as its down expression contributed to delay in seed germination in Arabidopsis by increasing abscisic acid level (Z. Liu et al, ). Moreover, the top upregulated genes such as Kunitz type trypsin inhibitor contained in legume seeds function as a protease inhibitor resulting in a complex resistance to proteolysis and protein metabolism (Meester, Brick, Lloyd, Blow, & Onesti, ). In the shortage of protein metabolism under waterlogging stress, the sensitive genotype may be employing the alternate fat metabolism which can be supported by GO enrichment analysis.…”

Poplar defense against insects: genome analysis, full‐length cDNA cloning, and transcriptome and protein analysis of the poplar Kunitz‐type protease inhibitor family

“…The composition of amino acids at the reactive loop is known to strongly influence the inhibitory function of protease inhibitors (Song & Suh, 1998;Ravichandran et al, 1999). Within this loop, the P1 and P1¢ residues (aa 86 and aa 87 of PtiKPI-F6) are considered the most critical for PI function (de Meester et al, 1998;Song & Suh, 1998). The P1 and P1¢ residues appear to be more strongly conserved in subfamilies A, B and C compared with subfamilies D, F and especially E. This sequence divergence is perhaps indicative of functional divergence between these subfamilies.…”

Kunitz trypsin inhibitor polymorphism in the Korean wild soybean (Glycine soja Sieb. & Zucc.)

“…Two major classes of proteinase inhibitors, antinutritional factors, namely Kunitz trypsin inhibitor (KTi) and Bowman-Birk trypsin inhibitor (BBTi) occupy about 6% of total seed storage protein in soybean (Wang et al 2004). Those of the KTi protein has an Mr (mass relative) of about 20 kDa with two disulphide bridges, while BBTi protein has an Mr of about 8 kDa with seven disulphide bridges (Meester et al 1998). KTi protein from G. max was first isolated and characterized by Kunitz (1947a,b) and was named after him as Kunitz trypsin inhibitor.…”