Summary: Hsp20/alpha crystallin family
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Hsp20 Edit Wikipedia article
|Hsp20/alpha crystallin family|
Heat shock protein Hsp20 is a family of heat shock proteins. Prokaryotic and eukaryotic organisms respond to heat shock or other environmental stress by inducing the synthesis of proteins collectively known as heat-shock proteins (hsp). Amongst them is a family of proteins with an average molecular weight of 20 kDa, known as the hsp20 proteins. These seem to act as protein chaperones that can protect other proteins against heat-induced denaturation and aggregation. Hsp20 proteins seem to form large heterooligomeric aggregates. Structurally, this family is characterised by the presence of a conserved C-terminal domain, alpha-crystallin domain, of about 100 residues. Recently, small heat shock proteins (sHSPs) were found in marine viruses (cyanophages).
Function and regulation
Hsp20, like all heat shock proteins, is in abundance when cells are under stressed conditions. Hsp20 is known to be expressed in many human tissues, including the brain and heart. Hsp20 has been studied extensively in cardiac myocytes and is known to act as a chaperon protein, binding to protein kinase 1 (PDK1) and allowing its nuclear transport. In addition, the phosphorylation of hsp20 has been shown to effect the structure of cells cytoskeletons. Due to hsp20 commonly forming dimers with itself when heated, its function of chaperoning can be greatly affected.
Human proteins containing this domain
- Lindquist S, Craig EA (1988). "The heat-shock proteins". Annu. Rev. Genet. 22: 631–677. doi:10.1146/annurev.ge.22.120188.003215. PMID 2853609.
- Merck KB, de Jong WW, Bloemendal H, Groenen PJ (1994). "Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology". Eur. J. Biochem. 225 (1): 1–9. doi:10.1111/j.1432-1033.1994.00001.x. PMID 7925426.
- Maaroufi H, Tanguay RM (2013). "Analysis and phylogeny of small heat shock proteins from marine viruses and their cyanobacteria host.". PLoS ONE. 8 (11): e81207. doi:10.1371/journal.pone.0081207. PMC . PMID 24265841.
- LI, D.C.; Lan, Fan; Chen, Dian-Fu; Yang, Wei-Jun; Lu, Bo. "Thermotolerance and molecular chaperone function of the small heat shock protein HSP20 from hyperthermophilic archaeon, Sulfolobus solfataricus P2". Cell Stress Chaperones. 17: 103–8. doi:10.1007/s12192-011-0289-z. PMC . PMID 21853411.
- G.C, Fan; G, Chu; EG, Kranies (May 2005). "Hsp20 and its cardioprotection". Trends Cardiovasc. Med. 15: 138–41. doi:10.1016/j.tcm.2005.05.004. PMID 16099377.
- Yan Sin, Yuan; Currie, Susan; P Martin, Lauren; Wills, Tamara; S Baillie, George. "Small heat shock protein 20 (Hsp20) facilitates nuclear import of protein kinase D 1 (PKD1) during cardiac hypertrophy". Cell Commun Signal. 13: 16. doi:10.1186/s12964-015-0094-x. PMC . PMID 25889640.
- M. Dreiza, Catherine; M. Brophy, Colleen; Komalavilas, Padmini; J. Furnish, Elizabeth; Joshi, Lokesh; A. Pallero, Manuel; E. Murphy-Ullrich, Joanne; von Rechenberg, Moritz; J. Ho, Yew-Seng; Richardson, Bonnie; Xu, Nafei; Zhen, Yuejun; M. Peltier, John; Panitch, Alyssa. "Transducible heat shock protein 20 (HSP20) phosphopeptide alters cytoskeletal dynamics". fasebj.org. The FASEB Journal. Retrieved November 6, 2016.
- van Montfort, RL; Basha, E; Friedrich, KL; Slingsby, C; Vierling, E. "Crystal structure and assembly of a eukaryotic small heat shock protein". http://europepmc.org. Europe PMC. Retrieved November 6, 2016. External link in
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.
Hsp20/alpha crystallin family Provide feedback
Not only do small heat-shock-proteins occur in eukaryotes and prokaryotes but they have also now been shown to occur in cyanobacterial phages as well as their bacterial hosts .
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR002068
Prokaryotic and eukaryotic organisms respond to heat shock or other environmental stress by inducing the synthesis of proteins collectively known as heat-shock proteins (hsp) [PUBMED:2853609]. Amongst them is a family of proteins with an average molecular weight of 20 Kd, known as the hsp20 proteins [PUBMED:7925426]. These seem to act as chaperones that can protect other proteins against heat-induced denaturation and aggregation. Hsp20 proteins seem to form large heterooligomeric aggregates.
These low-molecular-weight proteins are evolutionarily related to alpha-crystallin [PUBMED:6285380]. Alpha-crystallin is an abundant constituent of the eye lens of most vertebrate species. Its main function appears to be to maintain the correct refractive index of the lens. It is also found in other tissues where it seems to act as a chaperone [PUBMED:7925426]. Other related proteins include certain surface antigens [PUBMED:1370952].
This entry represents a conserved C-terminal domain of about 100 residues characteristic of this group of proteins [PUBMED:7723051].
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
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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.
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The small heat shock proteins (sHSPs) prevent protein aggregation during heat shock and oppose regulated cell death. A conserved arginine residue in the HSP20/alpha-crystallin domain (Pfam:PF00011) has in fact been implicated in the development of cataracts and myopathies . The CS family (Pfam:PF04969) includes proteins that are known to bind HSP90 , as well as p23 (Swiss:Q15185), which is an HSP90 co-chaperone .
The clan contains the following 4 members:CS GvpH HSP20 PIH1
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, the UniProtKB sequence database, the NCBI sequence database, and our metagenomics 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:
- 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 UniProtKB sequence database using the family HMM
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
- a Java applet developed at the University of Dundee. You will need Java installed before running jalview
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- an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.
You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.
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.
HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...
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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:||25|
|Number in full:||9559|
|Average length of the domain:||97.20 aa|
|Average identity of full alignment:||23 %|
|Average coverage of the sequence by the domain:||53.93 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 17690987 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||19|
|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:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
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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.
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 HSP20 domain has been found. There are 280 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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