Ready, set, fuse! The coronavirus spike protein and acquisition of fusion competence

Viruses. 2012 Apr;4(4):557-80. doi: 10.3390/v4040557. Epub 2012 Apr 12.


Coronavirus-cell entry programs involve virus-cell membrane fusions mediated by viral spike (S) proteins. Coronavirus S proteins acquire membrane fusion competence by receptor interactions, proteolysis, and acidification in endosomes. This review describes our current understanding of the S proteins, their interactions with and their responses to these entry triggers. We focus on receptors and proteases in prompting entry and highlight the type II transmembrane serine proteases (TTSPs) known to activate several virus fusion proteins. These and other proteases are essential cofactors permitting coronavirus infection, conceivably being in proximity to cell-surface receptors and thus poised to split entering spike proteins into the fragments that refold to mediate membrane fusion. The review concludes by noting how understanding of coronavirus entry informs antiviral therapies.

Keywords: membrane fusion; angiotensin converting enzyme 2; carcinoembryonic antigen; cathepsin; coronavirus; endocytosis; spike protein; transmembrane protease; viral pathogenesis; virus entry.

Publication types

  • Review

MeSH terms

  • Coronavirus / physiology*
  • Humans
  • Membrane Glycoproteins / metabolism*
  • Serine Proteases / metabolism
  • Spike Glycoprotein, Coronavirus
  • Viral Envelope Proteins / metabolism*
  • Virus Internalization*


  • Membrane Glycoproteins
  • Spike Glycoprotein, Coronavirus
  • Viral Envelope Proteins
  • Serine Proteases