The small heat-shock proteins IbpA and IbpB reduce the stress load of recombinant Escherichia coli and delay degradation of inclusion bodies -: art. no. 6

Background: The permanently impaired protein folding during recombinant protein production resembles the stress encountered at extreme temperatures, under which condition the putative holding chaperones, IbpA/IbpB, play an important role. We evaluated the impact of ibpAB deletion or overexpression on stress responses and the inclusion body metabolism during production of yeast alpha-glucosidase in Escherichia coli. Results: Deletion of ibpAB, which is innocuous under physiological conditions, impaired culture growth during alpha-glucosidase production. At higher temperatures, accumulation of stress proteins including disaggregation chaperones ( DnaK and ClpB) and components of the RNA degradosome, enolase and PNP, was intensified. Overexpression of ibpAB, conversely, suppressed the heat-shock response under these conditions. Inclusion bodies of alpha-glucosidase started to disaggregate after arrest of protein synthesis in a ClpB and DnaK dependent manner, followed by degradation or reactivation. IbpA/IbpB decelerated disaggregation and degradation at higher temperatures, but did hardly influence the disaggregation kinetics at 15 degrees C. Overexpression of ibpAB concomitant to production at 42 degrees C increased the yield of alpha-glucosidase activity during reactivation. Conclusions: IbpA/IbpB attenuate the accumulation of stress proteins, and - at high temperatures - save disaggregated proteins from degradation, at the cost, however, of delayed removal of aggregates.