Heterologous Expression, Purification, and Immune-Based Assay Application of Soluble SARS-CoV-2 Nucleocapsid Protein

Abstract

The serological monitoring of SARS-CoV-2 infection using the measurement of IgG is an important tool to determine the number of infected people in a population, and the disease spreading. One of the most important proteins from SARS-CoV-2 applied to immune-based assays is the nucleocapsid protein, also known as N protein. This is an abundant protein in the pathogen and exerts important functions in viral viability and replication. Moreover, protein N is highly immunogenic. The use of N protein as a recombinant protein is difficult since this biomolecule is mainly produced inside inclusion bodies in Escherichia coli. In this work, we present a simple and easy method for the expression and purification of soluble his-tagged N protein, suitable for serological assays, such as ELISA. ELISA assays using this recombinant protein presented 100% of specificity and 86% of sensitivity. The protocol for expression and purification of this recombinant protein can be applied in low infrastructure laboratories, without equipment dedicated to protein expression. This work may help other research groups to develop serological assays to monitor antibody production against SARS-CoV-2.