The mammalian small heat‐shock protein Hsp20 forms dimers and is a poor chaperone

• Published in: European journal of biochemistry Vol. 258; no. 3; pp. 1014 - 1021
• Main Authors: van de Klundert, Francy A. J. M., Smulders, Ronald H. P. H., Gijsen, Mariken L. J., Lindner, Robyn A., Jaenicke, Rainer, Carver, John A., de Jong, Wilfried W.
• Format: Journal Article
• Language: English
• Published: Berlin & Heidelberg Springer‐Verlag 15.12.1998
• Subjects: Amino Acid Sequence; Animals; chaperone‐like activity; dimer; Dimerization; DNA, Complementary - biosynthesis; DNA, Complementary - isolation & purification; Escherichia coli - genetics; Heat-Shock Proteins - chemistry; Heat-Shock Proteins - genetics; Heat-Shock Proteins - isolation & purification; HSP20 Heat-Shock Proteins; Humans; Mice; Molecular Chaperones - chemistry; Molecular Chaperones - genetics; Molecular Chaperones - isolation & purification; Molecular Sequence Data; Myocardium - chemistry; Nuclear Magnetic Resonance, Biomolecular; oligomer; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Phosphoproteins - chemistry; Phosphoproteins - genetics; Phosphoproteins - isolation & purification; protein structure; Rats; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; small heat‐shock protein
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1046/j.1432-1327.1998.2581014.x

Hsp20 is one of the newly described members of the mammalian small heat‐shock protein (sHsp) family. It occurs most abundantly in skeletal muscle and heart. We isolated clones for Hsp20 from a rat heart cDNA library, and expressed the protein in Escherichia coli to characterize this little known sHsp. Recombinant Hsp20 displayed similar far‐ultraviolet circular dichroism spectra as the most closely related sHsp, αB‐crystallin, but was less heat stable, denaturing upon heating to 50 +C. While other mammalian recombinant sHsps form large multimeric complexes, Hsp20 occurs in two complex sizes, 43‐kDa dimers and 470‐kDa multimers. The ratio between the two forms depends on protein concentration. Moreover, Hsp20 has a much lower chaperone‐like activity than αB‐crystallin, as indicated by its relatively poor capacity to diminish the reduction‐induced aggregation of insulin B chains. Hsp20 is considerably shorter at the C‐terminus and less polar than other sHsps, but 1H‐NMR spectroscopy reveals that the last 10 residues are flexible, as in the other sHsps. Our findings suggest that Hsp20 is a special member of the sHsp family in being less heat stable and tending to form dimers. These properties, together with the shorter and less polar C‐terminal extension, may contribute to the less effective chaperone‐like activity.