Extended Data Fig. 1: Schematic representations of the full-length SARS-CoV-2 and SARS-CoV spike proteins.

Segments of S1 and S2 include: NTD, N-terminal domain; RBD, receptor-binding domain; CTD1, C-terminal domain 1; CTD2, C-terminal domain 2; S1/S2, the furin cleavage site at the S1/S2 boundary; S2’, S2’ cleavage site; FP, fusion peptide; FPPR, fusion peptide proximal region; HR1, heptad repeat 1; CH, central helix region; CD, connector domain; HR2, heptad repeat 2; TM, transmembrane segment; CT, cytoplasmic tail; and tree-like symbols for glycans. Based on studies of the SARS-CoV S protein, three membranotropic regions in the SARS-CoV S2 have been suggested as putative fusion peptides, including a segment of residues 770–788, equivalent of the N-terminal FP in SARS-CoV S; a segment of residues 798–816 or 798–835, widely accepted as the “bona fide” FP; and a segment of residues 858–886, also equivalent of the internal FP in SARS-CoV S. A segment of residues 1190–1203 is called the pretransmembrane domain (pre-TM).