A subgenus of the betacoronaviruses, known as embecoviruses (not including SARS-like coronaviruses), have an additional shorter surface protein known as hemagglutinin esterase. For this reason the spike protein has been the focus of development for COVID-19 vaccines in response to the COVID-19 pandemic caused by the virus SARS-CoV-2. It is highly antigenic and accounts for most antibodies produced by the immune system in response to infection. : 33 Coronaviruses Ĭoronaviruses exhibit coronavirus spike protein, also known as the S protein, on their surfaces S is a class I fusion protein and is responsible for mediating viral entry as the first step in viral infection. Spikes or peplomers can be visible in electron micrograph images of enveloped viruses such as orthomyxoviruses, paramyxoviruses, rhabdoviruses, filoviruses, coronaviruses, bunyaviruses, arenaviruses, and retroviruses. Being exposed on the surface of the virion, spike proteins can be antigens. : 33 Many spike proteins are membrane fusion proteins. : 329 The binding site for the cell-surface receptor is usually located at the tip of the spike.
: 362 For example, influenza virus has two surface proteins with these two functions, hemagglutinin and neuraminidase. They may interact with cell-surface receptors located on the host cell and may have hemagglutinizing activity as a result, or in other cases they may be enzymes. Spikes typically have a role in viral entry. : 51–2 They are usually glycoproteins, more commonly via N-linked than O-linked glycosylation. They may also form protein–protein interactions with other viral proteins, such as those forming the nucleocapsid. Spike proteins are membrane proteins 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. Spikes or peplomers are usually rod- or club-shaped projections from the viral surface. More recently, the term "peplos" is considered a synonym for viral envelope. Early systems of viral taxonomy, such as the Lwoff- Horne- Tournier system proposed in the 1960s, used the appearance and morphology of the "peplos" and peplomers as important characteristics for classification. The term is derived from the Greek peplos, "a loose outer garment", "robe or cloak", or "woman mantle". The term "peplomer" refers to an individual spike from the viral surface collectively the layer of material at the outer surface of the virion has been referred to as the "peplos". : 29–33 The proteins are usually glycoproteins that form dimers or trimers. In virology, a spike protein or peplomer protein is a protein that forms a large structure known as a spike or peplomer projecting from the surface of an enveloped virus. 3D print of one of the trimeric spikes of SARS-CoV-2
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