Proteolytic processing of Middle East respiratory syndrome coronavirus spikes expands virus tropism

Proc Natl Acad Sci U S A. 2016 Oct 25;113(43):12262-12267. doi: 10.1073/pnas.1608147113. Epub 2016 Oct 10.


Middle East respiratory syndrome coronavirus (MERS-CoV) infects humans from zoonotic sources and causes severe pulmonary disease. Virions require spike (S) glycoproteins for binding to cell receptors and for catalyzing virus-cell membrane fusion. Fusion occurs only after S proteins are cleaved sequentially, first during their secretion through the exocytic organelles of virus-producing cells, and second after virus binding to target-cell receptors. To more precisely determine how sequential proteolysis contributes to CoV infection, we introduced S mutations obstructing the first cleavages. These mutations severely compromised MERS-CoV infection into human lung-derived cells, but had little effect on infection into several other cell types. These cell type-specific requirements for proteolysis correlated with S conformations during cell entry. Without the first cleavages, S proteins resisted cell receptor-induced conformational changes, which restricted the second, fusion-activating cleavages. Consistent with these findings, precleaved MERS viruses used receptor-proximal, cell-surface proteases to effect the second fusion-activating cleavages during cell entry, whereas the more rigid uncleaved MERS viruses trafficked past these cell-surface proteases and into endosomes. Uncleaved viruses were less infectious to human airway epithelial and Calu3 cell cultures because they lacked sufficient endosomal fusion-activating proteases. Thus, by sensitizing viruses to receptor-induced conformational changes, the first S cleavages expand virus tropism to cell types that are relevant to lung infection, and therefore may be significant determinants of MERS-CoV virulence.

Keywords: coronavirus; protease; receptor; virus entry.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coronavirus Infections / genetics*
  • Coronavirus Infections / virology
  • Gene Expression Regulation, Viral
  • Humans
  • Lung / pathology
  • Lung / virology*
  • Middle East Respiratory Syndrome Coronavirus / genetics*
  • Middle East Respiratory Syndrome Coronavirus / pathogenicity
  • Mutation
  • Proteolysis
  • Spike Glycoprotein, Coronavirus / genetics*
  • Viral Tropism / genetics
  • Virion / genetics
  • Virion / growth & development
  • Virus Internalization


  • Spike Glycoprotein, Coronavirus