Fig. 1.

Sequence and structural properties of the SARS-CoV-2 spike protein NTD. (A) Schematic representation of the SARS-CoV-2 spike protein domains. (B) Evolutionary relationship between different β-coronaviruses based on protein alignment of the NTD spike sequence. (C) β-coronaviruses NTD sequence alignment. Secondary structure of the SARS-CoV NTD (PDB ID: 5X4S) has been mapped to alignment indicating structural differences among the different members. (D) Cryo-EM structures of the SARS-CoV spike protein (left; PDB ID: 5X4S) and SARS-CoV-2 (right; PDB ID: 6VYB) indicating the β3-β4 (turquoise color), β9-β10 (blue color) and β14-β15 (red color) loop regions. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)