Phylogenetic analysis revealed that like SARS-CoV-1 and bat-derived SARS-like coronaviruses (SL-CoVs), SARS-CoV-2 belongs to lineage B of the betacoronavirus genus [8,9]. A study of 56 complete and partial SARS-CoV-2 genomes isolated from COVID-19 patients showed very high sequence conservation of more than 99%, indicating a recent introduction of the virus into the human population [10]. Although the animal source of SARS-CoV-2 is not clear, SARS-CoV-1 is believed to have originated from SL-CoVs residing in bats [11-14]. For the majority of SL-CoVs, the S1 subunit has low sequence identity to that of SARS-CoV-1, which suggests species-dependent receptor binding [14,15]. On the other hand, the high amino acid sequence identity of more than 90% in the S2 subunit suggests that the fusion mechanism during virus infection is well-conserved [14,15].