Spike protein functions

The S protein is a highly glycosylated and large type I transmembrane fusion protein that is made up of 1,160 to 1,400 amino acids, depending upon the type of virus.As compared to the M and E proteins that are primarily involved in virus assembly, the S protein plays a crucial role in penetrating host cells and initiating infection.Notably, the presence of S proteins on the coronaviruses is what gives rise to the spike-shaped protrusions found on their surface.S proteins of coronaviruses can be divided into two important functional subunits, which include the N-terminal S1 subunit, which forms the globular head of the S protein, and the C-terminal S2 region that forms the stalk of the protein and is directly embedded into the viral envelope.Upon interaction with a potential host cell, the S1 subunit will recognize and bind to receptors on the host cell, whereas the S2 subunit, which is the most conserved component of the S protein, will be responsible for fusing the envelope of the virus with the host cell membrane.