nCOV-2019 shares 76% sequence similarity with SARS-2002 spike protein, 73% sequence identity for RBD and 50% for the RBM.1 Bat coronavirus RaTG13 seems to be the closest relative of nCOV-2019 sharing about 93% sequence identity in the spike protein.6 The sequence alignment of SARS-2002 (accession number: AFR58742), SARS-civet (accession number: AY304486.1), Bat RaTG13 (accession number: MN996532.1), and nCOV-2019 (accession number: MN908947.1) is shown in Figure 2.6 To investigate the roles of critical mutations on the complex stability of nCOV-2019 with ACE2, mCSM-PPI2 webserver32 was used to find the residues in nCOV-2019 that are at the interface with ACE2.