Fig. 2.

Schematic of the virion, the genome and the spike protein of SARS-CoV-2 that causes COVID-19, a human respiratory syndrome. A) The viral surface, spike, envelope, and membrane proteins are embedded in a lipid bilayer and the single-stranded positive-sense viral RNA is associated with the nucleocapsid protein. The SARS-CoV-2 genome encompasses the 5′-untranslated region (5′-UTR), open reading frame (ORF) 1a/b encoding non-structural proteins for replication, ORFs encoding structural proteins including spike, envelop, membrane, and nucleocapsid proteins, ORFs encoding accessory proteins such as ORF 3a, 6, 7a, 7b, 8 and 10, and the 3′-UTR. B) Genome organization of SARS-CoV-2. C) SARS-CoV-2 spike glycoprotein. The S1/S2 cleavage sites are indicated by dotted lines. In the S protein, the S1 subunit is comprised of signal peptide (SP), receptor (ACE2)-binding motif (RBM), and receptor-binding domain (RBD); the S2 subunit is comprised of fusion peptide (FP), heptad repeat (HR), transmembrane domain (TM), and cytoplasm domain (CP).