Fusion expression, purification, and characterization of cytokeratin 19 fragments in E. coli for enhanced stability in diagnostic applications

Cytokeratin 19 fragment (CYFRA21-1) serves as a crucial tumor marker in the context of lung cancer patients, playing a pivotal role as a calibrator in the realm of in vitro diagnostics. Nevertheless, during practical application, it has come to light that the recombinantly synthesized full-length CYFRA21-1 antigen exhibits suboptimal stability at the requisite concentration, while the utilization of natural antigens incurs a substantial cost. To address this issue, our investigation harnessed a strategic approach whereby the soluble fragment of cytokeratin 19 (Aa244-400) was integrated into the pET32a vector, subsequently being expressed within E. coli through a fusion with the TrxA protein. This process involved induction of protein expression through 0.2 mM IPTG at 16 °C for a duration of 16 h. After induction, the target protein was purified through Ni affinity and ion exchange chromatography. Subsequent characterization of the targeted protein was executed through the SEC-HPLC technique. The attained CYFRA21-1 antigen, as generated within this study, was effectively incorporated into a chemiluminescence-based in vitro diagnostic detection kit. The results indicate that the fusion protein exhibited commendable reactivity and stability, manifesting a deviation of less than 10 % following incubation at 37 °C for 7 days. Importantly, the production yield achieved a notable magnitude of 300 mg/L, thus rendering it a cost-effective and scalable alternative to natural antigens for clinical diagnostic applications.