The spike protein is a protein that forms a large structure known as a spike or peplomer projecting from the surface of an enveloped virus. The spike protein is usually a glycoprotein that forms dimers or trimers and is a membrane protein with typically large external ectodomains, a single transmembrane domain that anchors the protein in the viral envelope, and a short tail in the interior of the virion. The spike protein is highly glycosylated and large type I transmembrane fusion protein that is made up of 1,160 to 1,400 amino acids. The spike protein is found on the surface of SARS-CoV-2, the virus that causes COVID-19, and it latches onto receptors known as angiotensin-converting enzyme 2 (ACE2) on target cells. The spike protein facilitates virus entry into healthy cells, which is the first step in infection. The spike protein is highly antigenic and accounts for most antibodies produced by the immune system in response to infection. The spike protein is unique to SARS-CoV-2 and doesnt look like other proteins the body makes, so antibodies created against the spike protein wont harm the body, they will only target coronavirus. The spike protein is also responsible for mediating viral entry as the first step in viral infection.