The virus spike protein decorates the outer surface of SARS-COV-2 virion and it is the target for the immune system and the antigen for all for vaccines reporting protection in phase 3 trials.
The illustration shows the conformational changes of the highly dynamic spike protein of the virus:
🟣 “Prefusion conformation”: the spike protein binds to the cellular receptor ACE2 and attaches to the cell membrane.
🟣 “Prehairpin and transient conformation”: cellular proteases cleave the spike protein inducing dramatical conformational changes on its structure.
🟣 “Postfusion state”: fusion with the cellular membrane and release of the viral genome.