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55  structures 124  species 3  interactions 766  sequences 4  architectures

Family: Kunitz_legume (PF00197)

Summary: Trypsin and protease inhibitor

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This is the Wikipedia entry entitled "Kunitz STI protease inhibitor". More...

Kunitz STI protease inhibitor Edit Wikipedia article

Trypsin and protease inhibitor
1TIE.png
Structure of a Kunitz-type trypsin inhibitor.[1]
Identifiers
Symbol Kunitz_legume
Pfam PF00197
InterPro IPR002160
PROSITE PDOC00255
SCOP 1tie
SUPERFAMILY 1tie

Kunitz soybean trypsin inhibitor is a type of protein contained in legume seeds which functions as a protease inhibitor.[2] Kunitz-type Soybean Trypsin Inhibitors are usually specific for either trypsin or chymotrypsin. They are thought to protect seeds against consumption by animal predators.

Background[edit]

Two types of trypsin inhibitors are found in soy: the Kunitz trypsin inhibitor (KTI) and the Bowman-Birk inhibitor (BBI). KTI is a large (20,100 daltons), strong inhibitor of trypsin, while BBI is much smaller (8,000 daltons) and inhibits both trypsin and chymotrypsin.[3] Both inhibitors have significant anti-nutritive effects in the body, affecting digestion by hindering protein hydrolysis and activation of other enzymes in the gut. In soy, KTI is found in much larger concentrations than BBI is soy, however, to achieve the highest nutritional value from this ingredient, both of these inhibitors must be denatured in some way. Whole soybeans have been reported to contain 17–27 mg of trypsin inhibitor per gram.

Structure[edit]

Proteins from the Kunitz family contain from 170 to 200 amino acid residues and one or two intra-chain disulfide 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)[1] and the bifunctional proteinase K/alpha-amylase inhibitor from wheat (PK13) have been solved, showing them to share the same 12-stranded beta sheet structure as those of interleukin 1 and heparin-binding growth factors.[4] The beta-sheets are arranged in 3 similar lobes around a central axis, 6 strands forming an anti-parallel beta 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 beta-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.

Action and Consequences of Trypsin Inhibitors[edit]

Trypsin inhibitors require a specific three-dimensional structure in order to follow through with inactivation of trypsin in the body. They bind strongly to trypsin, blocking its active site and instantly forming an irreversible compound and halting digestion of certain proteins. Trypsin, a serine protease, is responsible for cleaving peptide bonds containing carbonyl groups from arginine or lysine. After a meal, trypsin is stimulated by cholecystokinin and undergoes specific proteolysis for activation. Free trypsin is then able to activate other serine proteases, such as chymotrypsin, elastase, and more trypsin (by autocatalysis), or continue breaking down proteins.[5] However, if trypsin inhibitors (specifically KTI) are present, the majority of trypsin in the cycle of digestion is inactivated and ingested proteins remain whole. Effects of this occurrence include gastric distress, and pancreatic hyperplasia (proliferation of cells) or hypertrophy (enlargement of cells).[6] The amount of soy inhibitors is directly related to the amount of trypsin it will inhibit, therefore a product with high concentration of soy is suspect to produce large values of inhibition. In a rat model, animals were fed either soy protein concentrate or direct concentrate of the Kunitz trypsin inhibitor. In both instances, after a week the rats showed a dose-related increase in pancreas weight due to both hyperplasia and hypertrophy.[6] This indicates that long-term consumption of a diet high in soy with strong trypsin inhibitor activity may produce unwanted effects in humans as well.

Inactivation of Trypsin Inhibitors[edit]

A significant amount of research is being done to determine the best method of inhibitor inactivation. The most successful methods found so far include:

  • Heat
  • Freezing
  • Addition of Sulfites

Cancer Research[edit]

While trypsin inhibitors have been widely regarded as anti-nutritive factors in soy, research is currently being done on the inhibitors’ possible anti-carcinogenic characteristics. Some research has shown that protease inhibitors can cause irreversible suppressive effect on carcinogenic cell growth. However, the mechanism is still unknown. The cancers showing positive results for this new development are colon, oral, lung, liver, and esophageal cancers. Further research is still necessary to determine things such as the method of delivery for this natural anti-carcinogen, as well as performing extensive clinical trials in this area.[7]

References[edit]

  1. ^ a b PDB 1tie; Onesti S, Brick P, Blow DM (January 1991). "Crystal structure of a Kunitz-type trypsin inhibitor from Erythrina caffra seeds". J. Mol. Biol. 217 (1): 153–76. doi:10.1016/0022-2836(91)90618-G. PMID 1988676. 
  2. ^ Rawlings ND, Tolle DP, Barrett AJ (March 2004). "Evolutionary families of peptidase inhibitors". Biochem. J. 378 (Pt 3): 705–16. doi:10.1042/BJ20031825. PMC 1224039. PMID 14705960. 
  3. ^ [Soybean Protease Inhibitors in Foods], DiPietro CM, Liener IE, 1989. J Food Sci.
  4. ^ Murzin AG, Lesk AM, Chothia C (January 1992). "beta-Trefoil fold. Patterns of structure and sequence in the Kunitz inhibitors interleukins-1 beta and 1 alpha and fibroblast growth factors". J. Mol. Biol. 223 (2): 531–43. doi:10.1016/0022-2836(92)90668-A. PMID 1738162. 
  5. ^ [Principles of Biochemistry], Horton HR, Moran, LA, Scrimgeour KG, Perry MD, Rawn JD, 2006.
  6. ^ a b [Hypertrophy and hyperplasia of the rat pancreas produced by short-term dietary administration of soya-derived protein and soybean trypsin inhibitor], Smith JC, Wilson Fd, Allen PV, Berry DL, 1989. J Appl Toxic.
  7. ^ [The Role of Soy Products in Reducing Risk of Cancer], Messina M, Barnes S, 1991. J Natl Cancer Institute.

External links[edit]

This article incorporates text from the public domain Pfam and InterPro IPR002160

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

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Trypsin and protease inhibitor Provide feedback

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External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR002160

Peptide proteinase inhibitors can be found as single domain proteins or as single or multiple domains within proteins; these are referred to as either simple or compound inhibitors, respectively. In many cases they are synthesised as part of a larger precursor protein, either as a prepropeptide or as an N-terminal domain associated with an inactive peptidase or zymogen. This domain prevents access of the substrate to the active site. Removal of the N-terminal inhibitor domain either by interaction with a second peptidase or by autocatalytic cleavage activates the zymogen. Other inhibitors interact direct with proteinases using a simple noncovalent lock and key mechanism; while yet others use a conformational change-based trapping mechanism that depends on their structural and thermodynamic properties.

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, INTERPRO) and subtilisin (MEROPS peptidase family S8, INTERPRO), thiol proteinases (MEROPS peptidase family C1, INTERPRO) and aspartic proteinases (MEROPS peptidase family A1, INTERPRO) [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 beta-sheet structure as those of interleukin-1 and heparin-binding growth factors [PUBMED:1738162]. The beta-sheets are arranged in 3 similar lobes around a central axis, 6 strands forming an anti-parallel beta-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 beta-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.

Gene Ontology

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Domain organisation

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Pfam Clan

This family is a member of clan Trefoil (CL0066), which has the following description:

This family corresponds to a large set of related beta-trefoil proteins [1]. The beta-trefoil is formed by six two-stranded hairpins [2]. Three of these form a barrel structure and the other three are in a triangular array that caps the barrel. The arrangement of the secondary structures gives the molecules a pseudo 3-fold axis.

The clan contains the following 15 members:

AbfB Agglutinin Botulinum_HA-17 CDtoxinA DUF569 Fascin FGF FRG1 IL1 Ins145_P3_rec Kunitz_legume MIR Ricin_B_lectin RicinB_lectin_2 Toxin_R_bind_C

Alignments

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  Seed
(17)
Full
(766)
Representative proteomes NCBI
(793)
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(7)
RP35
(91)
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(97)
RP75
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  Seed
(17)
Full
(766)
Representative proteomes NCBI
(793)
Meta
(0)
RP15
(7)
RP35
(91)
RP55
(97)
RP75
(109)
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  Seed
(17)
Full
(766)
Representative proteomes NCBI
(793)
Meta
(0)
RP15
(7)
RP35
(91)
RP55
(97)
RP75
(109)
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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

External links

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Trees

This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

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Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

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Seed source: Prosite
Previous IDs: none
Type: Domain
Author: Finn RD
Number in seed: 17
Number in full: 766
Average length of the domain: 164.40 aa
Average identity of full alignment: 31 %
Average coverage of the sequence by the domain: 83.53 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.7 20.7
Trusted cut-off 21.3 21.1
Noise cut-off 20.1 20.1
Model length: 176
Family (HMM) version: 13
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Species distribution

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Interactions

There are 3 interactions for this family. More...

Alpha-amylase Thioredoxin Kunitz_legume

Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Kunitz_legume domain has been found. There are 55 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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