DnaK, Hsp70-protein complexes

Early attempts to determine the stoichiometry of hsp70-protein complexes by a correlation between Kj and log MM were unsuccessful because the substrate proteins are substantially unfolded in their complexes with hsp70. and hsp70s themselves probably deviate from a spherical shape to illustrate this point it should suffice to say that DnaK and DnaK-RCMLA complex behave as if they had apparent moleculcu masses of 93 and 156 kDa, respectively, when a correlation of log MM vs. Kd (using the same five standard proteins mentioned above plus bovine serum albumin dimer) was used to estimate moleculcir masses. 

Hsp70 proteins with their co-chaperones and cooperating chaperones thus constitute a complex network of folding machines. This chapter describes the molecular basis of this network. Particular emphasis is given to the DnaK system of Escherichia coli as it is the best understood Hsp70 system, and to the mechanistic differences between Hsp70 family members. 

Fig. 5. Model for sHsp chaperone activity. The sHsp oligomer (T Hspl6.9 shown here) is in rapid equilibrium with a smaller species (possibly a dimer). Heat-denatured substrates bind hydrophobic sites exposed on the sHsp subunits to form soluble sHsp/substrate complexes, preventing formation of insoluble aggregates of denatured proteins. The sHsp/substrate complexes may also be in rapid equilibrium, and when dissociated, the denatured substrate can be picked up and refolded in an ATP-dependent fashion by the Hsp70 or DnaK (plus cochaperone) machinery. Note that sHsp/substrate complexes can also become larger and insoluble, and the fate of these latter complexes is unknown.

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