Escherichia coli ‘TatExpress’ strains super-secrete human growth hormone into the bacterial periplasm by the Tat pathway

Numerous high-value proteins are secreted into the Escherichia coli periplasm by the General Secretory (Sec) pathway, but Sec-based production chassis cannot handle many potential target proteins. The Tat pathway offers a promising alternative because it transports fully folded proteins; however, yields have been too low for commercial use. To facilitate Tat export, we have engineered the TatExpress series of super-secreting strains by introducing the strong inducible bacterial promoter, ptac, upstream of the chromosomal tatABCD operon, to drive its expression in E. coli strains commonly used by industry (e.g. W3110 and BL21). This modification significantly improves the Tat-dependent secretion of human growth hormone (hGH) into the bacterial periplasm, to the extent that secreted hGH is the dominant periplasmic protein after only 1?h induction. TatExpress strains accumulate in excess of 30?mg?L?1 periplasmic recombinant hGH, even in shake flask cultures. A second target protein, an scFv, is also shown to be exported at much higher rates in TatExpress strain

Novel constructs and 1-step chromatography protocols for the production of Porcine Circovirus 2d (PCV2d) and Circovirus 3 (PCV3) subunit vaccine candidates

Porcine circovirus type 2 (PCV2) has been a major problem for the pig production industry worldwide for decades. While the majority of commercially available vaccines are based on the original PCV2a genotype, the current dominant genotype is PCV2d. The notable differences between genotypes could lead to incomplete cross-protection. Moreover, most current subunit PCV2 vaccines are generated from expensive insect cell culture technology. In this work, we present a new workflow for production of an updated and relatively inexpensive PCV2d vaccine candidate. After expression in fed-batch Escherichia coli fermentation systems with a simple one-step ion-exchange chromatography purification protocol, the yield of purified PCV2d-based antigen reached over 1 g per litre bacterial culture. Using similar procedures, we also demonstrated even higher PCV2d-based antigen yields from a chimeric PCV2d-PCV3 capsid construct, which is cleaved during fermentation to release PCV2d- and PCV3-related polypeptides. Although the PCV2d-based recombinant protein from this protocol did not form viral-like particles as analysed by size-exclusion chromatography, it could effectively induce capsid-specific and PCV2d-neutralising antibodies in immunised animals, indicating significant potential as a new vaccine candidate that can be easily manufactured at commercial scale

Evaluation of Methylotrophic Yeast Ogataea thermomethanolica TBRC 656 as a Heterologous Host for Production of an Animal Vaccine Candidate

Multiple yeast strains have been developed into versatile heterologous protein expression platforms. Earlier works showed that Ogataea thermomethanolica TBRC 656 (OT), a thermotolerant methylotrophic yeast, can efficiently produce several industrial enzymes. In this work, we demonstrated the potential of this platform for biopharmaceutical manufacturing. Using a swine vaccine candidate as a model, we showed that OT can be optimized to express and secrete the antigen based on porcine circovirus type 2d capsid protein at a respectable yield. Crucial steps for yield improvement include codon optimization and reduction of OT protease activities. The antigen produced in this system could be purified efficiently and induce robust antibody response in test animals. Improvements in this platform, especially more efficient secretion and reduced extracellular proteases, would extend its potential as a competitive platform for biopharmaceutical industries

Escherichia coli "TatExpress" strains export several g/L human growth hormone to the periplasm by the Tat pathway

Escherichia coli is a heavily used platform for the production of biotherapeutic and other high-value proteins, and a favored strategy is to export the protein of interest to the periplasm to simplify downstream processing and facilitate disulfide bond formation. The Sec pathway is the standard means of transporting the target protein but it is unable to transport complex or rapidly folding proteins because the Sec system can only transport proteins in an unfolded state. The Tat system also operates to transport proteins to the periplasm, and it has significant potential as an alternative means of recombinant protein production because it transports fully folded proteins. Here, we have tested the Tat system's full potential for the production of biotherapeutics for the first time using fed-batch fermentation. We expressed human growth hormone (hGH) with a Tat signal peptide in E. coli W3110 "TatExpress" strains that contain elevated levels of the Tat apparatus. This construct contained four amino acids from TorA at the hGH N-terminus as well as the initiation methionine from hGH, which is removed in vivo. We show that the protein is efficiently exported to the periplasm during extended fed-batch fermentation, to the extent that it is by far the most abundant protein in the periplasm. The protein was shown to be homogeneous, disulfide bonded, and active. The bioassay showed that the yields of purified periplasmic hGH are 5.4 g/L culture whereas an enzyme-linked immunosorbent assay gave a figure of 2.39 g/L. Separate analysis of a TorA signal peptide linked to hGH construct lacking any additional amino acids likewise showed efficient export to the periplasm, although yields were approximately two-fold lower