An effective approach for recombinant production of select SARS-CoV-2 proteins in Escherichia coli

Agah, Sayeh; Thorpe, Catherine; Chapman, Martin; Wuenschmann, Sabina

Rationale: Individuals with asthma may be at higher risk of becoming severely ill from COVID-19 which targets the respiratory tract and may cause asthma exacerbations. Serological testing can be useful to assess the true spread of COVID-19 and help protect vulnerable individuals. The SARS-CoV-2 spike and nucleocapsid proteins are the primary viral antigens against which antibodies are raised. We developed an efficient method for production of select SARS-CoV-2 proteins in E. coli to facilitate the development of diagnostics, research, and drug discovery. Methods: SARS-CoV-2 Spike-RBD, full-length Nucleocapsid, and Nucleocapsid RNA binding domain (BD), were expressed in E. coli under IPTG induction. The proteins were purified using multi-step chromatography techniques. The purity of the SARS-CoV-2 proteins was assessed by LC-MS/MS, and their IgG reactivity tested using COVID-19 positive patients’ sera by ELISA. Results: The Spike-RBD and Nucleocapsid proteins were expressed with high yields. The purified proteins had a relative abundance of >95% as assessed by LC-MS/MS with only trace contamination of host cell proteins. All three proteins showed high IgG reactivity (titers >1/10,000) against COVID-19 sera (n=50), with Spike-RBD and Nucleocapsid RNA-BD exhibiting the highest sensitivity. Conclusions: Production of high quality SARS-CoV-2 proteins is feasible in E.coli and the purified proteins will provide useful tools to study the immune responses involved in COVID-19 including antibody and T cell responses, epitope mapping, diagnostics and drug discovery.