Refolding of substrates bound to small Hsps relies on a disaggregation reaction mediated most efficiently by ClpB/DnaK.
Small heat shock proteins (sHsps) are ubiquitous molecular chaperones that bind denatured proteins in vitro, thereby facilitating their subsequent refolding by ATP-dependent chaperones. The mechanistic basis of this refolding process is poorly defined. We demonstrate that substrates complexed to sHsps from various sources are not released spontaneously. Dissociation and refolding of sHsp bound substrates relies on a disaggregation reaction mediated by the DnaK system, or, more efficiently, by ClpB/DnaK. While the DnaK system alone works for small, soluble sHsp/substrate complexes, ClpB/DnaK-mediated protein refolding is fastest for large, insoluble protein aggregates with incorporated sHsps. Such conditions reflect the situation in vivo, where sHsps are usually associated with insoluble proteins during heat stress. We therefore propose that sHsp function in cellular protein quality control is to promote rapid resolubilization of aggregated proteins, formed upon severe heat stress, by DnaK or ClpB/DnaK.
Mogk
Axel
A
ZMBH, Universität Heidelberg, Im Neuenheimer Feld 282, Heidelberg D-69120, Germany. a.mogk@zmbh.uni-heidelberg.de
Schlieker
Christian
C
Friedrich
Kenneth L
KL
Schönfeld
Hans-Joachim
HJ
Vierling
Elizabeth
E
Bukau
Bernd
B
D000818:Animals; D049071:Endopeptidase Clp; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006358:Hot Temperature; D008291:Malate Dehydrogenase / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D012995:Solubility
D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D008291:Malate Dehydrogenase; D049071:Endopeptidase Clp; C063842:dnaK protein, E coli; C069775:ClpB protein, E coli