Hsp20
{{Short description|Protein family}}
{{Pfam_box
| Symbol = HSP20
| Name = Hsp20/alpha crystallin family
| image =
| width =
| caption =
| Pfam= PF00011
| InterPro= IPR002068
| SMART=
| Prosite = PDOC00791
| SCOP = 1shs
| TCDB =
| OPM family=
| OPM protein=
| CDD= cd06464
| PDB=
{{PDB3|2byu}}I:47-137 {{PDB3|1gme}}A:47-150 {{PDB3|1shs}}F:46-147
}}
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).{{cite journal |vauthors=Lindquist S, Craig EA |title=The heat-shock proteins |journal=Annu. Rev. Genet. |volume=22 |pages=631–677 |year=1988 |pmid=2853609 | doi = 10.1146/annurev.ge.22.120188.003215 }} Amongst them is a family of proteins with an average molecular weight of 20 kDa, known as the hsp20 proteins.{{cite journal |vauthors=Merck KB, de Jong WW, Bloemendal H, Groenen PJ |title=Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology |journal=Eur. J. Biochem. |volume=225 |issue=1 |pages=1–9 |year=1994 |pmid=7925426 |doi=10.1111/j.1432-1033.1994.00001.x|doi-access=free }} 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).{{cite journal |vauthors=Maaroufi H, Tanguay RM |title=Analysis and phylogeny of small heat shock proteins from marine viruses and their cyanobacteria host. |journal=PLOS ONE |volume=8 |issue=11 |pages=e81207 |year=2013 |pmid=24265841 |doi=10.1371/journal.pone.0081207 |pmc=3827213|bibcode=2013PLoSO...881207M |doi-access=free }}
Function and regulation
Hsp20, like all heat shock proteins, is in abundance when cells are under stressed conditions.{{cite journal|last1=LI|first1=D.C.|last2=Lan|first2=Fan|last3=Chen|first3=Dian-Fu|last4=Yang|first4=Wei-Jun|last5=Lu|first5=Bo|title=Thermotolerance and molecular chaperone function of the small heat shock protein HSP20 from hyperthermophilic archaeon, Sulfolobus solfataricus P2|pmc=3227843|pmid=21853411|doi=10.1007/s12192-011-0289-z|volume=17|issue=1|journal=Cell Stress & Chaperones|pages=103–8|year=2012}} Hsp20 is known to be expressed in many human tissues, including the brain and heart.{{cite journal|last1=G.C|first1=Fan|last2=G|first2=Chu|last3=EG|first3=Kranies|title=Hsp20 and its cardioprotection|pmid=16099377|doi=10.1016/j.tcm.2005.05.004|volume=15|issue=4|date=May 2005|journal=Trends Cardiovasc. Med.|pages=138–41}} 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.{{cite journal|last1=Yan Sin|first1=Yuan|last2=Currie|first2=Susan|last3=P Martin|first3=Lauren|last4=Wills|first4=Tamara|last5=S Baillie|first5=George|title=Small heat shock protein 20 (Hsp20) facilitates nuclear import of protein kinase D 1 (PKD1) during cardiac hypertrophy|pmc=4356135|pmid=25889640|doi=10.1186/s12964-015-0094-x|volume=13|journal=Cell Commun Signal|pages=16|year=2015 |doi-access=free }} In addition, the phosphorylation of hsp20 has been shown to effect the structure of cells cytoskeletons.{{cite journal|last1=M. Dreiza|first1=Catherine|last2=M. Brophy|first2=Colleen|last3=Komalavilas|first3=Padmini|last4=J. Furnish|first4=Elizabeth|last5=Joshi|first5=Lokesh|last6=A. Pallero|first6=Manuel|last7=E. Murphy-Ullrich|first7=Joanne|last8=von Rechenberg|first8=Moritz|last9=J. Ho|first9=Yew-Seng|last10=Richardson|first10=Bonnie|last11=Xu|first11=Nafei|last12=Zhen|first12=Yuejun|last13=M. Peltier|first13=John|last14=Panitch|first14=Alyssa|title=Transducible heat shock protein 20 (HSP20) phosphopeptide alters cytoskeletal dynamics|journal=The FASEB Journal|volume=19|issue=2|pages=261–263|doi=10.1096/fj.04-2911fje|pmid=15598710|year=2005|doi-access=free |s2cid=28781928}} Due to hsp20 commonly forming dimers with itself when heated, its function of chaperoning can be greatly affected.{{cite journal|last1=van Montfort|first1=RL|last2=Basha|first2=E|last3=Friedrich|first3=KL|last4=Slingsby|first4=C|last5=Vierling|first5=E|title=Crystal structure and assembly of a eukaryotic small heat shock protein|journal=Nature Structural Biology|volume=8|issue=12|pages=1025–1030|doi=10.1038/nsb722|pmid=11702068|year=2001|s2cid=618916}}