Coronaviruses (CoVs) are common human and animal pathogens. In humans, four endemic CoV species together account for one third of mild respiratory infections worldwide. More severe and frequently fatal respiratory pathologies are caused by recent CoV outbreaks that resulted from occasional zoonotic spillover from animal CoV reservoirs, namely, SARS-CoV in 2002, MERS-CoV in 2012, and SARS-CoV-2 in 2019. Because CoVs threaten global health, any chance of relieving CoV’s threat on human populations would rely heavily on our understanding of the mechanistic requirements for CoV tropism, whose major determinant is at the level of viral entry. CoVs have evolved to use a single viral protein for entry: spike (S). The S protein binds viruses to host cell receptors and catalyzes virus-cell membrane fusion for entry. Uniquely, CoV S proteins contain at least two receptor binding domains, a domain A that generally engages host sialic acids, and a domain B that recognizes host transmembrane proteins. A putative advantage of this bivalent binding is elevated CoV zoonotic potential, for each binding domain can, theoretically, independently evolve affinity to distinct host factors. To test this hypothesis, we aimed to identify roles for each receptor for the S proteins of two beta-coronaviruses, the prototypic MHV-CoV strain JHM and human MERS-CoV. We focused on three distinct stages of the CoV life cycle: (1) CoV particle-cell binding; (2) CoV particle-cell entry; (3) CoV cell-to-cell spread via cell-cell fusion. For MHV-JHM S protein, we identified its interaction with host sialic acids. This interaction is responsible for the majority of the particle binding mediated by the S protein, which assists in JHM-CoV entry into various target cells, and is sufficient for cell-to-cell spread. For the S protein of MERS-CoV, we found its interaction with host sialic acids is similarly sufficient for cell-cell fusion. Furthermore, we identified single-nucleotide changes in both S protein-sialic acid binding S domain As that conferred elevated cell-binding and cell-cell fusion capabilities. This study highlights distinctive CoV receptor binding domain activities in the infection process and raise the possibility that CoVs utilizes them for facile zoonotic transmission and intercellular spread within infected organism.
|Commitee:||Uprichard, Susan, Campbell, Edward, Visick, Karen, Robia, Seth|
|School:||Loyola University Chicago|
|Department:||Microbiology and Immunology|
|School Location:||United States -- Illinois|
|Source:||DAI-B 81/11(E), Dissertation Abstracts International|
|Keywords:||Coronavirus, Membrane fusion, Sialic acids, Virus entry, Virus glycoproteins, Virus receptors|
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