Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2016 Oct 25;113(43):12262-12267. Epub 2016 Oct 10.

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

Author information

1
Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153.
2
Department of Pediatrics, University of Iowa, Iowa City, IA 52242.
3
Department of Microbiology, University of Iowa, Iowa City, IA 52242.
4
Department of Pediatrics, University of Iowa, Iowa City, IA 52242; Department of Microbiology, University of Iowa, Iowa City, IA 52242.
5
Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153; tgallag@luc.edu.

Abstract

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

PMID:
27791014
PMCID:
PMC5086990
DOI:
10.1073/pnas.1608147113
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center