Severe acute respiratory coronavirus 2 (SARS-CoV-2) belongs to the beta-coronavirus family. Coronaviruses are positive-sense, single-stranded RNA viruses, and have one of the largest genomes among RNA viruses.
Out of the 7 known coronaviruses that have infected humans so far, 4 (HCov-229E, HCoV-OC43, HCoV-NL63, CoV-HKU1) can cause seasonal, mild respiratory symptoms in healthy people. In contrast, the SARS-CoV-1 and Middle East respiratory syndrome coronavirus (MERS-CoV) are closely related to SARS-CoV-2 and have caused the 2002-2003 SARS and 2012 MERS epidemics, respectively. The current coronavirus disease of 2019 (COVID-19) pandemic is a global public health emergency with over 38 million cases and 1.08 million deaths worldwide to date.
The SARS-CoV-2 spike (S) glycoprotein
The surface of the SARS-CoV-2 virus has a spike (S) glycoprotein, which is a large homo-trimeric glycoprotein that forms a crown at the virus capsid surface. Each S protomer is further divided into two domains – S1 and S2