Side effects of chaperone gene co-expression in recombinant protein production

Abstract

Insufficient availability of molecular chaperones is observed as a major bottleneck for proper protein folding in recombinant protein production. Therefore, co-production of selected sets of cell chaperones along with foreign polypeptides is a common approach to increase the yield of properly folded, recombinant proteins in bacterial cell factories. However, unbalanced amounts of folding modulators handling folding-reluctant protein species might instead trigger undesired proteolytic activities, detrimental regarding recombinant protein stability, quality and yield. This minireview summarizes the most recent observations of chaperone-linked negative side effects, mostly focusing on DnaK and GroEL sets, when using these proteins as folding assistant agents. These events are discussed in the context of the complexity of the cell quality network and the consequent intricacy of the physiological responses triggered by protein misfolding.

Figure 1

Aimed to increase recombinant quality and solubility, co-production of individual chaperones or chaperone sets has been a common strategy since the role of these proteins in quality control has been solved, mainly involving protein holding to prevent aggregation, folding or refolding activities and disaggregation from inclusion bodies. Many studies report on the positive effects of chaperone gene co-expression, regarding solubility, yield, secretion ability and specific activity (green box). However, it is also true that this strategy has been largely controversial and the eventual success seen as highly product- and/or process-dependent. Also, more recent studies reveal that an excess of certain chaperones has negative effects on protein yield and other parameters related to protein quality (red box), mainly due to the role of chaperones in promoting proteolysis of folding reluctant proteins. This promotion of proteolysis seems to be mechanistically linked to the disaggregation activities ruled by DnaK [21,77].