Fermentation optimization of maltose-binding protein fused to neutrophil-activating protein from Escherichia coli TB1

Development of clone with novel TrpE fusion tag in E. coli for overexpression of trypsin in a bench-scale bioreactor

Trypsin is a key enzyme under the serine proteases that is found in the pancreas which plays a key role in protein digestion. It cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine. This enzyme has received greater attention mainly due to its increased use in the removal of fusion tags during protein purification and its role in the processing of biosimilars like insulin. The present study was carried out to develop a clone with Novel TrpLE1413(TrpE) Fusion Tag for enhanced expression of trypsin which helps in cost reduction of biosimilar processing. In our experiment we have used a synthetic bovine trypsin gene containing a novel fusion tag TrpE at its N terminus, which was cloned into the pET41b (+) vector and expressed in E. coli BL21 (DE3) in a lab-scale bioreactor. Using the optimized fermentation process with TrpE Fusion Tag, 27.8 g/L inclusion bodies were produced at the end of fermentation, of which 209 mg/L of active trypsin was obtained after purification. In contrast, previous reports have claimed to produce a maximum of 60 mg/L of the enzyme without the fusion tag. Thus based on our findings, the small size (less than 2 kDa) of TrpE tag and its hydrophobicity may reduce the loss incurred during the purification process. Hence, it could be discerned that the use of the TrpE fusion tag along with a robust fermentation process led to 3- 4 fold higher yield making it a commercially viable process facilitating an improved recovery of the enzyme.

Generation of novel trimeric fragments of human SP-A and SP-D after recombinant soluble expression in E. coli

Surfactant treatment for neonatal respiratory distress syndrome has dramatically improved survival of preterm infants. However, this has resulted in a markedly increased incidence of sequelae such as neonatal chronic inflammatory lung disease. The current surfactant preparations in clinical use lack the natural lung defence proteins surfactant proteins (SP)-A and D. These are known to have anti-inflammatory and anti-infective properties essential for maintaining healthy non-inflamed lungs.

Supplementation of currently available animal derived surfactant therapeutics with these anti-inflammatory proteins in the first few days of life could prevent the development of inflammatory lung disease in premature babies. However, current systems for production of recombinant versions of SP-A and SP-D require a complex solubilisation and refolding protocol limiting expression at scale for drug development.

Using a novel solubility tag, we describe the expression and purification of recombinant fragments of human (rfh) SP-A and SP-D using Escherichia coli without the need for refolding. We obtained a mean (± SD) of 23.3 (± 5.4) mg and 86 mg (± 3.5) per litre yield of rfhSP-A and rfhSP-D, respectively. rfhSP-D was trimeric and 68% bound to a ManNAc-affinity column, giving a final yield of 57.5 mg/litre of highly pure protein, substantially higher than the 3.3 mg/litre obtained through the standard refolding protocol. Further optimisation of this novel lab based method could potentially make rfhSP-A and rfhSP-D production more commercially feasible to enable development of novel therapeutics for the treatment of lung infection and inflammation.