Evaluation of Immunogenic Response of Recombinant Nucleocapsid Protein of SARS-CoV-2

Abstract

The outbreak of SARS-CoV-2 posed a great peril to humans worldwide. One critical requirement for controlling this disease is a rapid and reliable diagnostic procedure. RT-PCR is the widely used test for detecting SARS-CoV-2 but this method has several drawbacks. An automated ELISA platform has a greater testing ability as compared to PCR assays. Nucleocapsid (N) is a highly immunogenic protein, which is expressed abundantly during infection, and it has fewer mutations as compared to the other structural proteins of SARS-CoV-2. In this study, N-protein was PCR amplified, cloned, and expressed in E. coli BL21-CodonPlus-RIPL cells. The protein, expressed as inclusion bodies, was solubilized in 8 M tris-urea buffer (pH 6.8) and purified through Ni⁺² affinity chromatography. Validation of the protein against 319 COVID-19 patient plasma samples by using quantitative ELISA, showed a sensitivity of 30.7% with a specificity of 98%. 3-D modeling and C-PORT analysis were performed, which showed that the epitopes were generally accessible for interaction. This protein when used in combination with other epitope-rich constructs can produce results of acceptable sensitivity level for diagnosis of COVID-19.