The impact of dnaKJ overexpression on recombinant protein solubility results from antagonistic effects on the control of protein quality

We have produced increasing levels of DnaK and its co-chaperone DnaJ along with the model VP1LAC misfolding-prone protein, to explore the role of DnaK on the management of Escherichia coli inclusion bodies. While relative solubility of VP1LAC is progressively enhanced, the heat-shock response is down-regulated as revealed by decreasing levels of GroEL. This is accompanied by an increasing yield of VP1LAC and a non-regular evolution of its insoluble fraction, at moderate levels of DnaK resulting in more abundant inclusion bodies. Also, the impact of chaperone co-expression is much more pronounced in wild type cells than in a DnaK- mutant, probably due to the different background of heat shock proteins in these cells. The involvement of DnaK in the supervision of misfolding proteins is then pictured as a dynamic balance between its immediate holding and folding activities, and the side-effect downregulation of the heat shock response though the limitation of other chaperone and proteases activities.