Cloning and Expression of SARS COV-2 Surface Protein and its Use in Detecting Corona Viral Infections

The main aim of this study was to develop indirect enzyme linked immune sorbent assay based on the use of bacterial cloned SARS CoV-2 spike protein as a cheap and continuously available source of antigen. This test was proved to be useful for a quantitative measurement and evaluation of antibody immune response among SARS-CoV-2 infected individuals. Standard cloning procedures had been used in cloning two different segments of the spike gene and its expression. The size of the two cloned segments were of 700 base pair and of 500 base pair, which were named clone 8 and clone 105, respectively. These DNA segments were cloned in pET28a plasmid and then expressed in Bl21 E. coli. Different serum samples were tested from: current, previous infection, vaccinated and non-vaccinated patients using the amplified expressed proteins in enzyme linked immune sorbent assay. The expressed proteins from each clone were responded with varying degrees of sensitivity against COVID-19 positive human sera, and we attempted to validate which of the two recombinant proteins is the best to be used in Corona IgG and IgM antibody detection. Based on the results of indirect enzyme linked immunoassay, most of the tested samples had greater antibody titers with clone 8, which was found to have a higher similarity (99% resemblance) to the severe acute respiratory syndrome coronavirus 2 surface protein using BLAST search. We recommend clone 8 with high potential to be used for large-scale screening for COVID-19 outbreak; nevertheless, it requires greater sensitivity and specificity validation