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381  structures 7235  species 0  interactions 28946  sequences 216  architectures

Family: HSP20 (PF00011)

Summary: Hsp20/alpha crystallin family

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Hsp20 Edit Wikipedia article

Hsp20/alpha crystallin family

The heat shock protein Hsp20 family, also known as small heat shock proteins (sHSPs), 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).[1] Amongst them is a family of proteins with an average molecular weight of 20 kDa, known as the hsp20 proteins.[2] 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).[3]

Function and regulation

Hsp20, like all heat shock proteins, is in abundance when cells are under stressed conditions.[4] Hsp20 is known to be expressed in many human tissues, including the brain and heart.[5] 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.[6] In addition, the phosphorylation of hsp20 has been shown to effect the structure of cells cytoskeletons.[7] Due to hsp20 commonly forming dimers with itself when heated, its function of chaperoning can be greatly affected.[8]

Human small heat shock proteins


  1. ^ Lindquist S, Craig EA (1988). "The heat-shock proteins". Annu. Rev. Genet. 22: 631–677. doi:10.1146/ PMID 2853609.
  2. ^ 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.
  3. ^ 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. Bibcode:2013PLoSO...881207M. doi:10.1371/journal.pone.0081207. PMC 3827213. PMID 24265841.
  4. ^ LI, D.C.; Lan, Fan; Chen, Dian-Fu; Yang, Wei-Jun; Lu, Bo (2012). "Thermotolerance and molecular chaperone function of the small heat shock protein HSP20 from hyperthermophilic archaeon, Sulfolobus solfataricus P2". Cell Stress Chaperones. 17 (1): 103–8. doi:10.1007/s12192-011-0289-z. PMC 3227843. PMID 21853411.
  5. ^ G.C, Fan; G, Chu; EG, Kranies (May 2005). "Hsp20 and its cardioprotection". Trends Cardiovasc. Med. 15 (4): 138–41. doi:10.1016/j.tcm.2005.05.004. PMID 16099377.
  6. ^ Yan Sin, Yuan; Currie, Susan; P Martin, Lauren; Wills, Tamara; S Baillie, George (2015). "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 4356135. PMID 25889640.
  7. ^ 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 (2005). "Transducible heat shock protein 20 (HSP20) phosphopeptide alters cytoskeletal dynamics". The FASEB Journal. 19 (2): 261–263. doi:10.1096/fj.04-2911fje. PMID 15598710.
  8. ^ van Montfort, RL; Basha, E; Friedrich, KL; Slingsby, C; Vierling, E (2001). "Crystal structure and assembly of a eukaryotic small heat shock protein". Nature Structural Biology. 8 (12): 1025–1030. doi:10.1038/nsb722. PMID 11702068.
This article incorporates text from the public domain Pfam and InterPro: IPR002068

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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 [2].

Literature references

  1. Kim KK, Kim R, Kim SH , Nature 1998;394:595-599.: Crystal structure of a small heat-shock protein. PUBMED:9707123 EPMC:9707123

  2. Maaroufi H, Tanguay RM;, PLoS One. 2013;8:e81207.: Analysis and phylogeny of small heat shock proteins from marine viruses and their cyanobacteria host. PUBMED:24265841 EPMC:24265841

Internal database links

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 and transparency of the lens. It is also found in other tissues where it seems to act as a chaperone [ PUBMED:7925426 , PUBMED:22120592 ]. 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 ].

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan HSP20 (CL0190), which has the following description:

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 [1]. The CS family (Pfam:PF04969) includes proteins that are known to bind HSP90 [2], as well as p23 (Swiss:Q15185), which is an HSP90 co-chaperone [3].

The clan contains the following 6 members:

ArsA_HSP20 CS GvpH HSP20 PIH1_CS Pih1_fungal_CS


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...

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Curation and family details

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Seed source: Prosite
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Sonnhammer ELL
Number in seed: 25
Number in full: 28946
Average length of the domain: 97.20 aa
Average identity of full alignment: 23 %
Average coverage of the sequence by the domain: 53.70 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.8 20.8
Trusted cut-off 20.8 20.8
Noise cut-off 20.7 20.7
Model length: 102
Family (HMM) version: 23
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Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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 381 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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