SARS-CoV-2 Spike Protein S1 (RBD):Fc (human) (rec.) (B.1.617 Variant, IND)

SARS-CoV-2 shares 79.5% sequence identity with SARS-CoV and is 96.2% identical at the genome level to the bat coronavirus BatCoV RaTG133, suggesting it had originated in bats. The coronaviral genome encodes four major structural proteins: the Spike (S) protein, Nucleocapsid (N) protein, Membrane/Matrix (M) protein and the Envelope (E) protein. The SARS Envelope (E) protein contains a short palindromic transmembrane helical hairpin that seems to deform lipid bilayers, which may explain its role in viral budding and virion envelope morphogenesis. The SARS Membrane/Matrix (M) protein is one of the major structural viral proteins. It is an integral membrane protein involved in the budding of the viral particles and interacts with SARS Spike (S) protein and the Nucleocapsid (N) protein. The N protein contains two domains, both of them bind the virus RNA genome via different mechanisms. The CoV Spike (S) protein assembles as trimer and plays the most important role in viral attachment, fusion and entry. It is composed of a short intracellular tail, a transmembrane anchor and a large ectodomain that consists of a receptor binding S1 subunit (RBD domain) and a membrane-fusing S2 subunit. The S1 subunit contains a receptor binding domain (RBD), which binds to the cell surface receptor angiotensin-converting enzyme 2 (ACE2) present at the surface of epithelial cells. Recently, a new variant of SARS-CoV-2, called B.1.617 was detected in India. Three sublineages have been found, B.1.617.1 (variant Kappa) and B.1.617.3 containing 4 mutations in the Spike protein with a double mutations in the Receptor Binding Region (L452R, E484Q) and B.1.617.2 (variant Delta) that is different since it contains the mutation T478K instead of E484Q. These variants (especially the B.1.617.1 & B.1.617.2) of the SARS-CoV-2 coronavirus have evolved as fast-growing variants outspacing other variants. Protein function: [Spike protein S1]: attaches the virion to the cell membrane by interacting with host receptor, initiating the infection. Binding to human ACE2 receptor and internalization of the virus into the endosomes of the host cell induces conformational changes in the Spike glycoprotein (PubMed:32142651, PubMed:32221306, PubMed:32075877, PubMed:32155444). Binding to host NRP1 and NRP2 via C-terminal polybasic sequence enhances virion entry into host cell (PubMed:33082294, PubMed:33082293). This interaction may explain virus tropism of human olfactory epithelium cells, which express high level of NRP1 and NRP2 but low level of ACE2 (PubMed:33082293). The stalk domain of S contains three hinges, giving the head unexpected orientational freedom (PubMed:32817270). Uses human TMPRSS2 for priming in human lung cells which is an essential step for viral entry (PubMed:32142651). Can be alternatively processed by host furin (PubMed:32362314). Proteolysis by cathepsin CTSL may unmask the fusion peptide of S2 and activate membranes fusion within endosomes. [The UniProt Consortium]