title: Proteolytic processing of Middle East respiratory syndrome coronavirus spikes expands virus tropism.
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.
authors: Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153.
authors: Jung-Eun
authors: JE
authors: Park
authors: Department of Pediatrics, University of Iowa, Iowa City, IA 52242.
authors: Kun
authors: K
authors: Li
authors: Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153.
authors: Arlene
authors: A
authors: Barlan
authors: Department of Microbiology, University of Iowa, Iowa City, IA 52242.
authors: Anthony R
authors: AR
authors: Fehr
authors: Department of Pediatrics, University of Iowa, Iowa City, IA 52242; Department of Microbiology, University of Iowa, Iowa City, IA 52242.
authors: Stanley
authors: S
authors: Perlman
authors: Department of Pediatrics, University of Iowa, Iowa City, IA 52242; Department of Microbiology, University of Iowa, Iowa City, IA 52242.
authors: Paul B
authors: PB
authors: McCray
authors: Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153; tgallag@luc.edu.
authors: Tom
authors: T
authors: Gallagher
mesh_terms: D018352:Coronavirus Infections / Q000235:genetics* / Q000821:virology; D015967:Gene Expression Regulation, Viral; D006801:Humans; D008168:Lung / Q000473:pathology / Q000821:virology*; D065207:Middle East Respiratory Syndrome Coronavirus / Q000235:genetics* / Q000472:pathogenicity; D009154:Mutation; D059748:Proteolysis; D064370:Spike Glycoprotein, Coronavirus / Q000235:genetics*; D056189:Viral Tropism / Q000235:genetics; D014771:Virion / Q000235:genetics / Q000254:growth & development; D053586:Virus Internalization
chemical_list: D064370:Spike Glycoprotein, Coronavirus
keywords: coronavirus; protease; receptor; virus entry