CoV-S[679-833]

General information on CoV-S [679-833]

Enveloped viruses, such as SARS-CoV-2 the causative agent of COVID-19, enter their host by a process of membrane fusion mediated by a protein exposed in the viral envelop. In the new coronavirus strain, this protein is the spike glycoprotein (protein S) which is a trimeric transmembrane component of the viral envelop. This protein initiates the complex process of receptor binding and membrane fusion, that triggers viral internalization and subsequently the beginning of the virus replication cycle.
Within this protein, several domains play crucial roles in this complex process. In the specific case of SARS-CoV-2, the spike protein is a class I fusion protein which means that after binding the angiotensin-converting enzyme 2 (ACE2) receptor, the protein needs to be primed for fusion by proteolytic cleavage. For this reason, understanding protein cleavage is key to understanding viral pathogenesis in SARS-CoV-2.
The 155 amino acid long region comprised between residues 679 and 833 represents the boundary between the S1 and S2 subunits of the spike glycoprotein in SARS-CoV-2. Researchers have found that the S1/S2 boundary contains a polybasic cleavage site between residues R685 and S686. Furin, a widespread human intracellular protease that recognizes this site, is thus responsible for exposing the fusion domain and initiating viral entry.
The presence of a polybasic cleavage site in this new strain of coronavirus potentially explains its expanded tropism (ability to infect different types of tissue) and increased transmissibility in comparison to SARS-CoV, the virus responsible for the 2003 pandemic.
Designing vaccines or therapeutic antibodies to target this region has the potential of blocking the fusion of the cellular and viral membranes, and subsequently of preventing the infection in its early stages.