InterPro domain: 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) [ 1 ]. Amongst them is a family of proteins with an average molecular weight of 20 Kd, known as the hsp20 proteins [ 2 ]. 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 [ 3 ]. 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 [ 4 , 4 ]. Other related proteins include certain surface antigens [ 5 ].

This entry represents a conserved C-terminal domain of about 100 residues characteristic of this group of proteins [ 6 ].

1. The heat-shock proteins. Annu. Rev. Genet. 22, 631-77
2. Structure and modifications of the junior chaperone alpha-crystallin. From lens transparency to molecular pathology. Eur. J. Biochem. 225, 1-19
3. Four small Drosophila heat shock proteins are related to each other and to mammalian alpha-crystallin. Proc. Natl. Acad. Sci. U.S.A. 79, 2360-4
4. Acetylation of αA-crystallin in the human lens: effects on structure and chaperone function. Biochim. Biophys. Acta 1822, 120-9
5. The 14,000-molecular-weight antigen of Mycobacterium tuberculosis is related to the alpha-crystallin family of low-molecular-weight heat shock proteins. J. Bacteriol. 174, 1352-9
6. The expanding small heat-shock protein family, and structure predictions of the conserved "alpha-crystallin domain". J. Mol. Evol. 40, 238-48