Designing next generation recombinant protein expression platforms by modulating the cellular stress response in Escheri
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Microbial Cell Factories Open Access
RESEARCH
Designing next generation recombinant protein expression platforms by modulating the cellular stress response in Escherichia coli Richa Guleria1†, Priyanka Jain1†, Madhulika Verma2 and Krishna J. Mukherjee1,3*
Abstract Background: A cellular stress response (CSR) is triggered upon recombinant protein synthesis which acts as a global feedback regulator of protein expression. To remove this key regulatory bottleneck, we had previously proposed that genes that are up-regulated post induction could be part of the signaling pathways which activate the CSR. Knocking out some of these genes which were non-essential and belonged to the bottom of the E. coli regulatory network had provided higher expression of GFP and L-asparaginase. Results: We chose the best performing double knockout E. coli BW25113ΔelaAΔcysW and demonstrated its ability to enhance the expression of the toxic Rubella E1 glycoprotein by 2.5-fold by tagging it with sfGFP at the C-terminal end to better quantify expression levels. Transcriptomic analysis of this hyper-expressing mutant showed that a significantly lower proportion of genes got down-regulated post induction, which included genes for transcription, translation, protein folding and sorting, ribosome biogenesis, carbon metabolism, amino acid and ATP synthesis. This down-regulation which is a typical feature of the CSR was clearly blocked in the double knockout strain leading to its enhanced expression capability. Finally, we supplemented the expression of substrate uptake genes glpK and glpD whose down-regulation was not prevented in the double knockout, thus ameliorating almost all the negative effects of the CSR and obtained a further doubling in recombinant protein yields. Conclusion: The study validated the hypothesis that these up-regulated genes act as signaling messengers which activate the CSR and thus, despite having no casual connection with recombinant protein synthesis, can improve cellular health and protein expression capabilities. Combining gene knockouts with supplementing the expression of key down-regulated genes can counter the harmful effects of CSR and help in the design of a truly superior host platform for recombinant protein expression. Keywords: Cellular stress response, Escherichia coli, Knockouts, Recombinant protein expression, Signaling, Transcriptome
*Correspondence: [email protected]; [email protected] † Richa Guleria and Priyanka Jain equally contributed to this work 1 School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India Full list of author information is available at the end of the article
Background Protein synthesis is an energy intensive process and the diversion of metabolites and energy for recombinant protein production elicits a cellular stress response (CSR) [1, 2], which combines the features of the generalized stress response, the heat shock, oxidative stress and the stringent response [3–6]. This CSR can be perceived as a defense mechanism by which the cell sa
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