SARS-CoV-2 (2019nCoV, novel Coronavirus) Spike protein, S1 Protein, Spike S1-NTD, Spike S1-CTD, Spike-RBD and Spike trimer protein.

1. SARS-CoV-2 (2019nCoV) Spike protein: SARS-CoV-2, a newly emerged pathogen spreading worldwide. The transmembrane spike (S) glycoprotein of SARS-CoV-2 that forms homotrimers protruding from the viral surface is known to mediate coronavirus entry into host cells. It has been reported that spike protein can bind with high affinity to human ACE2 and uses it as an entry receptor to invade target cells.

2. SARS-CoV-2 (2019nCoV) spike S1 protein: The spike protein is a large type I transmembrane glycoprotein comprises two functional subunits, S1 and S2. S1 subunit of spike protein is responsible for binding to the host cell receptor. S2 subunit is responsible for fusion of the viral and cellular membranes.

3. SARS-CoV-2 (2019nCoV) spike S1-NTD and S1-CTD: For most coronaviruses, the N-terminal domain (NTD) of the S1 subunit attaches to cellular carbohydrates and the C-terminal domain of S1 (S1-CTD) binds to a cellular protein receptor. Carbohydrate binding by the S1 N-terminal domain is thought to keep the virus in close proximity to the host cell surface, whereas engagement of specific protein receptors by the S1-CTD is thought to initiate a series of conformational changes in the spike that ultimately result in membrane fusion and delivery of the viral genome to the cytosol.

4. SARS-CoV-2 (2019nCoV) Spike RBD: S1 subunit of spike protein contains a receptor binding domain (RBD), which is responsible for recognizing the cell surface receptor.

5. SARS-CoV-2 (2019nCoV) Spike trimer protein: The transmembrane spike (S) glycoprotein of SARS-CoV-2 usually forms homotrimers protruding from the viral surface. S trimers are extensively decorated with N-linked glycans that are important for proper folding and for modulating accessibility to host proteases and neutralizing Abs. It has been found that S glycoprotein trimers in highly pathogenic human coronaviruses appear to exist in partially opened states, while they remain largely closed in human coronaviruses associated with common colds.