Prevention and reversion of protein aggregation by molecular chaperones in the E. coli cytosol: implications for their applicability in biotechnology.

The amount of a native protein reflects an equilibrium of protein synthesis, de novo folding and protein stability. Stress situations, like heat shock, or overproduction of a protein can cause an imbalance in this equilibrium, resulting in protein aggregation. Molecular chaperones control protein folding processes and protect misfolded proteins from aggregation in all cells. Since protein aggregation is frequently observed upon synthesis of heterologous proteins in E. coli, molecular chaperones have been applied in biotechnology by their co-overproduction with the desired protein. While increasing protein solubility in some cases, this approach has not been generally successful. Recent findings demonstrate, that protein aggregation, even in case of inclusion bodies, must not be a dead end in the life cycle of a protein. Such resolubilization of aggregated proteins is mediated by a bi-chaperone system consisting of ClpB and DnaK, the prokaryotic representatives of the Hsp100 and Hsp70 families. The disaggregation capacity of this bi-chaperone system has now been demonstrated in vitro and in vivo for a wide variety of aggregated proteins and offers a new perspective to increase the solubility of proteins of interest.