The mammalian small heat-shock protein Hsp20 forms dimers and is a poor chaperone.
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, alpha B-crystallin, but was less heat stable, denaturing upon heating to 50 degrees 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 alpha B-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.
van de Klundert
F A
FA
Department of Biochemistry, University of Nijmegen, The Netherlands.
Smulders
R H
RH
Gijsen
M L
ML
Lindner
R A
RA
Jaenicke
R
R
Carver
J A
JA
de Jong
W W
WW
D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000096:biosynthesis / Q000302:isolation & purification; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D050886:HSP20 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D051379:Mice; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism