STI Soybean trypsin inhibitor (Kunitz) family of protease inhibitors
SMART ACC:	SM000452
Description:	-
InterPro ACC:	IPR002160
InterPro abstract:	The Kunitz-type soybean trypsin inhibitor (STI) family consists mainly of proteinase inhibitors from Leguminosae seeds [ PUBMED:14705960 ]. They belong to MEROPS inhibitor family I3, clan IC. They exhibit proteinase inhibitory activity against serine proteinases; trypsin (MEROPS peptidase family S1, expand The Kunitz-type soybean trypsin inhibitor (STI) family consists mainly of proteinase inhibitors from Leguminosae seeds [ PUBMED:14705960 ]. They belong to MEROPS inhibitor family I3, clan IC. They exhibit proteinase inhibitory activity against serine proteinases; trypsin (MEROPS peptidase family S1, IPR001254 ) and subtilisin (MEROPS peptidase family S8, IPR000209 ), thiol proteinases (MEROPS peptidase family C1, IPR000668 ) and aspartic proteinases (MEROPS peptidase family A1, IPR001461 ) [ PUBMED:14705960 ]. Inhibitors from cereals are active against subtilisin and endogenous alpha-amylases, while some also inhibit tissue plasminogen activator. The inhibitors are usually specific for either trypsin or chymotrypsin, and some are effective against both. They are thought to protect the seeds against consumption by animal predators, while at the same time existing as seed storage proteins themselves - all the actively inhibitory members contain 2 disulphide bridges. The existence of a member with no inhibitory activity, winged bean albumin 1, suggests that the inhibitors may have evolved from seed storage proteins. Proteins from the Kunitz family contain from 170 to 200 amino acid residues and one or two intra-chain disulphide bonds. The best conserved region is found in their N-terminal section. The crystal structures of soybean trypsin inhibitor (STI), trypsin inhibitor DE-3 from the Kaffir tree Erythrina caffra (ETI) [ PUBMED:1988676 ] and the bifunctional proteinase K/alpha-amylase inhibitor from wheat (PK13) have been solved, showing them to share the same 12-stranded β-sheet structure as those of interleukin-1 and heparin-binding growth factors [ PUBMED:1738162 ]. The β-sheets are arranged in 3 similar lobes around a central axis, 6 strands forming an anti-parallel β-barrel. Despite the structural similarity, STI shows no interleukin-1 bioactivity, presumably as a result of their primary sequence disparities. The active inhibitory site containing the scissile bond is located in the loop between β-strands 4 and 5 in STI and ETI. The STIs belong to a superfamily that also contains the interleukin-1 proteins, heparin binding growth factors (HBGF) and histactophilin, all of which have very similar structures, but share no sequence similarity with the STI family. collapse
GO function:	endopeptidase inhibitor activity (GO:0004866)
Family alignment:	View the Family alignment or the Alignment consensus sequence
There are 1 624 STI domains in 1 614 proteins in SMART's NRDB database.

Taxonomic distribution of proteins containing STI domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing STI domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Relevant references for this domain

Primary literature for the STI domain is listed below. Automatically-derived, secondary literature is also available.

KEGG pathways involving proteins which contain this domain

This information is based on the mapping of SMART genomic protein database to KEGG orthologous groups. Percentages are related to the number of proteins containing a STI domain which could be assigned to a KEGG orthologous group, and not all proteins containing STI domains. Please note that proteins can be included in multiple pathways, ie. the numbers below will not add to 100%.

KEGG pathways

KEGG orthologous groups

3D structures in PDB containing this domain

Links to other resources describing this domain

InterPro	IPR002160
PROSITE	SOYBEAN_KUNITZ
Pfam	Kunitz_legume