The epidemic severe respiratory disease COVID-19 also known as nCOV, SARS-CoV-2 is an enveloped virus containing a positive ssRNA genome. SARS-CoV-2 belongs to the family of beta-Corona virus that also includes other life threatening viruses like SARS and MERS. This large family of potential viruses has become the major pathogens for emerging respiratory disease outbreaks and can be isolated from different animal species.

The structural proteins of coronavirus include the spike protein (S), the envelope (E) protein, the membrane (M) protein, and the nucleocapsid protein (N) Out of these proteins the spike (S) protein and nucleocapsid protein (N) play an important role in viral pathogenesis.

The COVID-19 spike protein (S) facilitates its entry to the target cells. S protein consists of two subunits, S1 and S2. The spike S1 subunit contains a stretch conserved amino acid, called Receptor Binding Domain (RBD), which facilitates viral attachment to a cell surface receptor, angiotensin-converting enzyme 2 (ACE2). The viral entry also requires spike protein S2 of the S protein for fusion of viral and cellular membranes. COVID-19 uses angiotensin-converting enzyme 2 (ACE2) as the entry receptor. It has also been demonstrated that initial spike protein priming by transmembrane protease serine 2 (TMPRSS2) is essential for entry and viral spread of SARS-CoV-2 through interaction with the ACE2 receptor. A number of studies has shown that antibody against RBD can interfere with binding of virus to the surface ACE2 receptor, thus preventing viral entry in to the cell. Blocking TMPRSS2 with inhibitors like Camostat (mesylate) and E-64d is also an option for inhibition of viral entry.

Nucleocapsid (N) protein has multiple functions involving nuclear-import signal, interfering cell process, virus replication and RNA package. In addition, N protein is highly immunogenic and abundantly expressed during infection, which makes it an ideal candidate for raising neutralizing antibodies and diagnostic applications.