4. Possible vaccine candidates for COVID-19
Since the SARS-CoV-2 shares a considerable genetic sequence homology and sequence identity of various essential enzymes with SARS-CoV (Hui et al., 2020; Zhu et al., 2020; Perlman 2020; Zhou et al., 2020), the vaccine strategies already built for SARS could potentially facilitate the early design of COVID-19 vaccine (Morse et al., 2020; Chen et al., 2020). Both SARS-CoV-2 and SARS-CoV bind to similar ACE2 receptors of human lungs (Hoffmann et al., 2020; Zhou et al., 2020). Similar to other CoVs, genome of SARS-CoV-2 translates four major structural proteinsviz . nucleocapsid protein (N), spike glycoprotein (S), membrane glycoprotein (M), and envelop protein (E) (Saif, 2020). The S protein is the major focus in vaccine development because it contains receptor binding domain (RBD), functions in viral attachment via S1 subunit, fuses with host cell via S2 subunit, and strongly induces VN antibodies which blocks binding with the host receptor cells in lungs (Zhou et al., 2020). However, M protein has the ability to induce VN antibodies and N protein contains T-cell epitopes in SARS-CoV, which means they can also act as an efficient vaccine targets (Rauch et al., 2018; Roper and Rehm 2009; Enjuanes et al., 2008).