Summary: Kazal-type serine protease inhibitor domain
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Kazal domain Edit Wikipedia article
|Kazal-type serine protease inhibitor domain|
the structure of the follistatin:activin complex
|SCOPe||3sgb / SUPFAM|
|Kazal-type serine protease inhibitor domain|
structure of fs1, the heparin-binding domain of follistatin
|SCOPe||3sgb / SUPFAM|
The Kazal domain is an evolutionary conserved protein domain usually indicative of serine protease inhibitors. However, kazal-like domains are also seen in the extracellular part of agrins, which are not known to be protease inhibitors.
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.
This family of Kazal inhibitors, belongs to MEROPS inhibitor family I1, clan IA. They inhibit serine peptidases of the S1 family (INTERPRO). The members are primarily metazoan, but includes exceptions in the alveolata (apicomplexa), stramenopiles, higher plants and bacteria.
Kazal inhibitors, which inhibit a number of serine proteases (such as trypsin and elastase), belong to family of proteins that includes pancreatic secretory trypsin inhibitor; avian ovomucoid; acrosin inhibitor; and elastase inhibitor. These proteins contain between 1 and 7 Kazal-type inhibitor repeats.
The structure of the Kazal repeat includes a large quantity of extended chain, 2 short alpha-helices and a 3-stranded anti-parallel beta sheet. The inhibitor makes 11 contacts with its enzyme substrate: unusually, 8 of these important residues are hypervariable. Altering the enzyme-contact residues, and especially that of the active site bond, affects the strength of inhibition and specificity of the inhibitor for particular serine proteases. The presence of this Pfam domain is usually indicative of serine protease inhibitors, however, Kazal-like domains are also seen in the extracellular part of agrins which are not known to be proteinase inhibitors.
Human proteins with Kazal 1 domains:
- AGRIN, CPAMD8
- FST, FSTL3, FSTL4, FSTL5
- SMOC1, SPARC, SPARCL1, SPINK1, SPINK2, SPINK4, SPINK5, SPINK5L2, SPINK5L3, SPINK6, SPINK7, SPINK9
- TMEFF1, TMEFF2
This domain is usually indicative of serine protease inhibitors that belong to Merops inhibitor families: I1, I2, I17 and I31. However, kazal-like domains are also seen in the extracellular part of agrins, which are not known to be protease inhibitors. Kazal domains often occur in tandem arrays and have a central alpha-helix, a short two-stranded antiparallel beta-sheet and several disulphide bonds. The amino terminal segment of this domain binds to the active site of its target proteases, thus inhibiting their function.
Human proteins with Kazal 2 domains:
- C6, CFI
- FSTL1, FSTL3
- HTRA1, HTRA3, HTRA4
- IGFBP7, KAZALD1, LST3, RECK
- SLC21A8, SLCO1A2, SLCO1B1, SLCO1B3, SLCO1C1, SLCO2A1, SLCO3A1, SLCO4A1, SLCO4C1, SLCO5A1, SLCO6A1, SMOC2, SPINK5, SPOCK1, SPOCK2, SPOCK3
- WFIKKN1, WFIKKN2
- MEROPS family I1
- InterPro: IPR001239
- Rawlings ND, Tolle DP, Barrett AJ (March 2004). "Evolutionary families of peptidase inhibitors". Biochem. J. 378 (Pt 3): 705â€“16. doi:10.1042/BJ20031825. PMC 1224039. PMID 14705960.
- Williamson MP; Marion D; WÃ¼thrich K (March 1984). "Secondary structure in the solution conformation of the proteinase inhibitor IIA from bull seminal plasma by nuclear magnetic resonance". J. Mol. Biol. 173 (3): 341â€“59. doi:10.1016/0022-2836(84)90125-6. PMID 6699915.
- Laskowski M, Kato I, Ardelt W, Cook J, Denton A, Empie MW, Kohr WJ, Park SJ, Parks K, Schatzley BL (January 1987). "Ovomucoid third domains from 100 avian species: isolation, sequences, and hypervariability of enzyme-inhibitor contact residues". Biochemistry. 26 (1): 202â€“21. doi:10.1021/bi00375a028. PMID 3828298.
- Empie MW, Laskowski M (May 1982). "Thermodynamics and kinetics of single residue replacements in avian ovomucoid third domains: effect on inhibitor interactions with serine proteinases". Biochemistry. 21 (10): 2274â€“84. doi:10.1021/bi00539a002. PMID 7046785.
- Schlott B, WÃ¶hnert J, Icke C, Hartmann M, Ramachandran R, GÃ¼hrs KH, Glusa E, Flemming J, GÃ¶rlach M, Grosse F, OhlenschlÃ¤ger O (April 2002). "Interaction of Kazal-type inhibitor domains with serine proteinases: biochemical and structural studies". J. Mol. Biol. 318 (2): 533â€“46. doi:10.1016/S0022-2836(02)00014-1. PMID 12051857.
- Stubbs MT, Morenweiser R, StÃ¼rzebecher J, Bauer M, Bode W, Huber R, Piechottka GP, Matschiner G, Sommerhoff CP, Fritz H, Auerswald EA (August 1997). "The three-dimensional structure of recombinant leech-derived tryptase inhibitor in complex with trypsin. Implications for the structure of human mast cell tryptase and its inhibition". J. Biol. Chem. 272 (32): 19931â€“7. doi:10.1074/jbc.272.32.19931. PMID 9242660.
- van de Locht A, Lamba D, Bauer M, Huber R, Friedrich T, KrÃ¶ger B, HÃ¶ffken W, Bode W (November 1995). "Two heads are better than one: crystal structure of the insect derived double domain Kazal inhibitor rhodniin in complex with thrombin". EMBO J. 14 (21): 5149â€“57. PMC 394622. PMID 7489704.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Kazal-type serine protease inhibitor domain Provide feedback
Usually indicative of serine protease inhibitors. However, kazal-like domains are also seen in the extracellular part of agrins, which are not known to be protease inhibitors. Kazal domains often occur in tandem arrays. Small alpha+beta fold containing three disulphides.
Internal database links
|SCOOP:||Kazal_1 MFS_1 OATP|
|Similarity to PfamA using HHSearch:||Kazal_1|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR002350
Canonical serine proteinase inhibitors are distributed in a wide range of organisms from all kingdoms of life and play crucial role in various physiological mechanisms [ PUBMED:6996568 ]. They interact from the canonical proteinase-inhibitor binding loop, where P1 residue has a predominant role (the residue at the P1 position contributing the carbonyl portion to the reactive-site peptide bond). These so-called canonical inhibitors bind to their cognate enzymes in the same manner as a good substrate, but are cleaved extremely slowly. Kazal-type inhibitors represent the most studied canonical proteinase inhibitors. Kazal inhibitors are extremely variable at their reactive sites. However, some regularity prevails such as the presence of lysine at position P1 indicating strong inhibition of trypsin [ PUBMED:10708867 ].
The Kazal inhibitor has six cysteine residues engaged in disulfide bonds arranged as shown in the following schematic representation:
+------------------+ | | *******************|*** xxxxxxxxCxxxxxxCx#xxxxxCxxxxxxxxxxCxxCxxxxxxxxxxxxxxxxxC | | | | | +-------------|-----------------+ +----------------------------+ 'C': conserved cysteine involved in a disulfide bond. '#': active site residue. '*': position of the pattern.
The structure of classical Kazal domains consists of a central alpha helix, which is inserted between two beta-strands and a third that is toward the C terminus [ PUBMED:6752426 ]. The reactive site P1 and the conformation of the reactive site loop is structurally highly conserved, similar to the canonical conformation of small serine proteinase inhibitors.
This entry represents the Kazal domain.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||protein binding (GO:0005515)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
The graphic that is shown by default represents the longest sequence with a given architecture. Each row contains the following information:
- the number of sequences which exhibit this architecture
a textual description of the architecture, e.g. Gla, EGF x 2, Trypsin.
This example describes an architecture with one
Gladomain, followed by two consecutive
EGFdomains, and finally a single
- a link to the page in the Pfam site showing information about the sequence that the graphic describes
- the UniProt description of the protein sequence
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Note that you can see the family page for a particular domain by clicking on the graphic. You can also choose to see all sequences which have a given architecture by clicking on the Show link in each row.
Finally, because some families can be found in a very large number of architectures, we load only the first fifty architectures by default. If you want to see more architectures, click the button at the bottom of the page to load the next set.
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Kazal domains are found in both serine protease inhibitors and extracellular regions of agrins. The structure of the Kazal domain is a small alpha/beta fold. Typically the Kazal domain consists of 2 short-helices and a 3-stranded anti-parallel sheet. The fold is contains several disulphide bonds.
The clan contains the following 3 members:Kazal_1 Kazal_2 Kazal_3
We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets and the UniProtKB sequence database. More...
There are various ways to view or download the sequence alignments that we store. We provide several sequence viewers and a plain-text Stockholm-format file for download.
We make a range of alignments for each Pfam-A family:
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- 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 UniProtKB sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
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We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
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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.
Note: You can also download the data file for the tree.
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.
|Number in seed:||40|
|Number in full:||20608|
|Average length of the domain:||47.20 aa|
|Average identity of full alignment:||30 %|
|Average coverage of the sequence by the domain:||13.52 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||17|
|Download:||download the raw HMM for this family|
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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.
Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.
If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.
For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
You can use the tree controls to manipulate how the interactive tree is displayed:
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Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
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 Kazal_2 domain has been found. There are 49 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 sequence.
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AlphaFold Structure Predictions
The list of proteins below match this family and have AlphaFold predicted structures. Click on the protein accession to view the predicted structure.