Heterologous expression, purification and single step efficient refolding of recombinant tissue plasminogen activator...

Reteplase (recombinant plasminogen activator, rPA) is a mutant non-glycosylated tissue-type plasminogen activator (tPA) containing 355 amino acids with longer half-life and promising thrombolytic activity than its original counterpart, full length tPA. In this study, we aimed to produce and optimize the purification process of recombinant tissue-type plasminogen activator (tPA) known as Reteplase (rPA). Reteplase cDNA synthesized from total mRNA isolated from human placenta was PCR amplified, cloned into a pET-28a(+) E. coli expression vector and expressed in Rosetta-gami 2 E. coli (Novagen^Ⓡ) host. rPA was expressed as an inclusion body in E. coli and its biological activity was achieved after single step solubilization, purification and refolding. We exploited the strategy of Slow Refolding using Gradual Dialysis (SRGD) in which a refolding buffer containing glutathione oxidized (1 mM GSSG) and glutathione reduced (3 mM GSH) and pH 9.0 was used. Using the SRGD method, we were able to successfully obtain the protein in its active form. We obtained 4.26 mg of active refolded protein from a 50 mL culture that was scaled up in a bioreactor. The purity and homogeneity of rPA was evaluated by SDS-PAGE, Western blotting and mass spectrometry. Circular dichroism spectroscopy was conducted to evaluate the refolding and stability of the refolded rPA in comparison to reference standard rPA. The thrombolytic potential of rPA was assessed by fibrin plate assay and In Vitro clot lysis assay. The presented protocol offers a viable approach for enhancing both the yield and refolding efficiency of reteplase, potentially resulting in an increase in yield.