Solubility and Refolding
In E coli, recombinant proteins usually accumulate in the cytoplasm, and examples where recombinant protein constitutes up to 30 percent of total cellular protein can be found in the literature. However, excessive production is not without drawbacks, as the recombinant protein will sometimes misfold and aggregate into so-called inclusion bodies. While inclusion body formation might be advantageous in some cases due to resistance to proteolytic degradation, the subsequent solubilisation and refolding of the inclusion bodies is expensive and results in reduced yield.
Low solubility and inclusion bodies are the main problems when proteins are expressed in the cytoplasm. To circumvent them, you may lower the temperature, substitute amino acids, co-express chaperones, use a large, hydrophilic fusion partner (such as GST), change culture conditions, e.g. pH, or change the bacterial strain. from all these possible approaches, low the temperature from 37°C to 25°C or even 16°C and reduction of inducer IPTG from 1mM to 0.05 mM are used as a routine protocol at Exon BioSystems. Alternatively, inclusion bodies may be solubilized and refolded to get functionality and active products. Inclusion body induction and purification has some advantages, such as high protein induction level, better purification and less protein degradation. The down side is the difficulty of protein refolding. Protein refolding is often inefficiently refolded, and most of the protein will be aggregated. At the same time, the folded protein will have low activity or no activity at all.
Suggestion: avoid protein refolding if possible.
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