Summary: Squash family serine protease inhibitor
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Squash family serine protease inhibitor Provide feedback
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External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000737
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 squash inhibitors form one of a number of serine proteinase inhibitor families. They belong to MEROPS inhibitor family I7, clan IE. They are generally annotated as either trypsin or elastase inhibitors (MEROPS peptidase family S1, INTERPRO). The proteins, found exclusively in the seeds of the cucurbitaceae, e.g. Citrullus lanatus (watermelon), Cucumis sativus (cucumber), Momordica charantia (balsam pear), are approximately 30 residues in length and contain 6 Cys residues, which form 3 disulphide bonds [PUBMED:2914611]. The inhibitors function by being taken up by a serine protease (such as trypsin), which cleaves the peptide bond between Arg/Lys and Ile residues in the N-terminal portion of the protein [PUBMED:1731946, PUBMED:2914611]. Structural studies have shown that the inhibitor has an ellipsoidal shape, and is largely composed of beta-turns [PUBMED:2914611]. The fold and Cys connectivity of the proteins resembles that of potato carboxypeptidase A inhibitor [PUBMED:1731946].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||serine-type endopeptidase inhibitor activity (GO:0004867)|
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The members of this clan are all cystine rich domains, which form a knottin scaffold. This clan should also contain alpha-amylase but currently this family is a singleton and can not be put into Pfam. Also see .
The clan contains the following 2 members:CarbpepA_inh Squash
We make a range of alignments for each Pfam-A family:
- the curated alignment from which the HMM for the family is built
- the alignment generated by searching the sequence database using the HMM
- Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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Curation and family details
|Number in seed:||12|
|Number in full:||37|
|Average length of the domain:||28.70 aa|
|Average identity of full alignment:||64 %|
|Average coverage of the sequence by the domain:||90.24 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||13|
|Download:||download the raw HMM for this family|
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There are 2 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
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 Squash domain has been found. There are 32 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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