Size-dependent Disaggregation of Stable Protein Aggregates by the DnaK Chaperone Machinery

Abstract

Classic in vitro studies show that the Hsp70 chaperone system from Escherichia coli (DnaK-DnaJ-GrpE, the DnaK system) can bind to proteins, prevent aggregation, and promote the correct refolding of chaperone-bound polypeptides into native proteins. However, little is known about how the DnaK system handles proteins that have already aggregated. In this study, glucose-6-phosphate dehydrogenase was used as a model system to generate stable populations of protein aggregates comprising controlled ranges of particle sizes. The DnaK system recognized the glucose-6-phosphate dehydrogenase aggregates as authentic substrates and specifically solubilized and refolded the protein into a native enzyme. The efficiency of disaggregation by the DnaK system was high with small aggregates, but the efficiency decreased as the size of the aggregates increased. High folding efficiency was restored by either excess DnaK or substoichiometric amounts of the chaperone ClpB. We suggest a mechanism whereby the DnaK system can readily solubilize small aggregates and refold them into active proteins. With large aggregates, however, the binding sites for the DnaK system had to be dynamically exposed with excess DnaK or the catalytic action of ClpB and ATP. Disaggregation by the DnaK machinery in the cell can solubilize early aggregates that formed accidentally during chaperone-assisted protein folding or that escaped the protection of "holding" chaperones during stress.

The yeast prion protein Ure2: Structure, function and folding

“…This is consistent with the cellular role of Hsp104 in disassembly of existing protein aggregates, in cooperation with the Hsp70 chaperone system [87,88].…”

Firefly luciferase mutants as sensors of proteome stress

“…Hsp70 members are highly multifunctional proteins that have been shown to play a key role in proteome maintenance, such as in de novo protein folding (co-or post-translational), protein translocation across membranes (Lyman and Schekman, 1997;Matlack et al, 1999;Young et al, 2003), refolding of stress damaged proteins (Ben-Zvi et al, 2004;Schroder et al, 1993;Sharma et al, 2010), in preventing protein aggregation (Auluck et al, 2002;Broadley and Hartl, 2009;Klucken et al, 2004;Sakahira et al, 2002;Warrick et al, 1999), disaggregation (Ben-Zvi and Goloubinoff, 2001;Diamant et al, 2000;Liberek et al, 2008;Shorter, 2011) and degradation of irreparable misfolded proteins (Bercovich et al, 1997;Fisher et al, 1997;Urushitani et al, 2004). These essential and diverse cellular functions of Hsp70 are attributed to its physical interaction with various co-chaperones such as Hsp40, NEFs and with proteins such as HIP, HOP and CHIP.…”

Controlled Expression of Recombinant Proteins in Physcomitrella patens by a Conditional Heat-shock Promoter: a Tool for Plant Research and Biotechnology

“…The GUS activity of the purified fraction was correlated on SDS-PAGE with a standard curve of Coomassie blue-stained GUS bands and of a known amount of the G6PDH enzyme (Diamant et al, 2000).…”