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#E. coli expression

3 public questions tagged with this topic.

Gene Cloning Process

What change improves protein solubility in E. coli expression systems?

Lowering post-induction temperature to 16-25°C markedly improves solubility of recombinant proteins expressed in Escherichia coli. Reduced temperature slows transcription and translation rates, decreasing nascent chain concentration and allowing more time for co-translational folding assisted by chaperones GroEL and DnaK. Hydrophobic interactions driving aggregation are temperature dependent and weakened at lower temperatures, thus inclusion body formation is minimized. High IPTG or high temperature exacerbates aggregation, while glucose suppresses induction via catabolite repression but does not enhance folding quality of already induced protein.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Gene Cloning Process

Insoluble expression of protein X at 37°C in E. coli is due to:

High-level expression of heterologous proteins at 37°C in Escherichia coli under strong promoters like T7 drives rapid polypeptide synthesis exceeding the capacity of endogenous chaperone systems such as GroEL-GroES and DnaK. Hydrophobic stretches improperly exposed interact intermolecularly, forming insoluble aggregates termed inclusion bodies sequestered in cytoplasm. Although protein is abundant, it is misfolded and functionally inactive. This aggregation is temperature and induction rate dependent rather than due to promoter absence, inducer failure, or cytotoxicity, and can be mitigated by lowering culture temperature or using solubility tags.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Gene Cloning Process

Why might a eukaryotic protein expressed in E. coli remain non-functional?

Expression of eukaryotic proteins in prokaryotic host Escherichia coli often yields inactive product due to multiple physiological mismatches. Codon bias differs; rare eukaryotic codons cause ribosome stalling, premature termination, and truncation. Prokaryotes lack endoplasmic reticulum machinery for N-glycosylation, disulfide isomerization, and other post-translational modifications essential for stability and activity. Molecular chaperone systems and folding environments also differ, leading to misfolding, aggregation into inclusion bodies, and proteolytic degradation. Combined effects explain multifactorial loss of function requiring eukaryotic hosts or engineered bacterial strains for rescue.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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