Monitoring of genes that respond to overproduction of an insoluble recombinant protein in Escherichia coli glucose-limited fed-batch fermentations.

The cellular response of Escherichia coli to overproduction of the insoluble heterologous protein α-glucosidase of Saccharomyces cerevisiae during a glucose-limited fed-batch fermentation was analyzed on the transcriptional and the translational levels. After the induction of the tac-regulated overexpression of the recombinant model protein, a significant but transient increase of the mRNA levels of the heat shock genes lon and dnaK could be observed. The mRNA level of the gene coding for the inclusion body-associated protein IbpB showed the strongest increase and remained at a clearly higher level until the end of the fermentation. By contrast, the mRNA levels of htrA and ppiB were decreased after induction of the α-glucosidase overexpression. Analysis of the soluble cytoplasmic protein fraction 3 h after induction revealed increased levels of the chaperones GroEL, DnaK, and Tig and a decrease in the protein levels of the two ribosomal proteins S6 and L9, the peptidylprolyl-cis-trans-isomerase PpiB, and the σ38-dependent protein Dps. Analysis of the aggregated protein fraction revealed a remarkably inhomogeneous composition of the α-glucosidase inclusion bodies. N-terminal sequencing and MALDI-TOF mass spectrometry identification showed that most of these spots are fragments of the heterologous α-glucosidase. Host stress proteins, like DnaK, GroEL, IbpA, IbpB, and OmpT, have been found to be associated with the α-glucosidase protein aggregates. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 217–224, 2000.