Attachment of Mouse Hepatitis Virus to O-Acetylated Sialic Acid Is Mediated by Hemagglutinin-Esterase and Not by the Spike Protein

ABSTRACT The members of Betacoronavirus phylocluster A possess two types of surface projections, one comprised of the spike protein (S) and the other of hemagglutinin-esterase (HE). Purportedly, these viruses bind to O-acetylated sialic acids (O-Ac-Sias) primarily through S, with HE serving merely as receptor-destroying enzyme. Here, we show that, in apparent contrast to human and ungulate host range variants of Betacoronavirus-1, murine coronaviruses actually bind to O-Ac-Sias via HE exclusively. Apparently, expansion of group A betacoronaviruses into new hosts and niches was accompanied by changes in HE ligand and substrate preference and in the roles of HE and S in Sia receptor usage.

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Identification of the Receptor-Binding Domain of the Spike Glycoprotein of Human Betacoronavirus HKU1

Journal of Virology ◽

10.1128/jvi.03737-14 ◽

2015 ◽

Vol 89 (17) ◽

pp. 8816-8827 ◽

Cited By ~ 19

Author(s):

Zhaohui Qian ◽

Xiuyuan Ou ◽

Luiz Gustavo Bentim Góes ◽

Christina Osborne ◽

Anna Castano ◽

...

Keyword(s):

Receptor Binding ◽

Hepatitis Virus ◽

Mouse Hepatitis Virus ◽

Binding Domain ◽

Spike Protein ◽

Receptor Binding Domain ◽

Spike Glycoprotein ◽

S Protein ◽

Receptor Proteins ◽

Group A

ABSTRACTCoronavirus spike (S) glycoproteins mediate receptor binding, membrane fusion, and virus entry and determine host range. Murine betacoronavirus (β-CoV) in group A uses the N-terminal domain (NTD) of S protein to bind to its receptor, whereas the β-CoVs severe acute respiratory syndrome CoV in group B and Middle East respiratory syndrome CoV in group C and several α-CoVs use the downstream C domain in their S proteins to recognize their receptor proteins. To identify the receptor-binding domain in the spike of human β-CoV HKU1 in group A, we generated and mapped a panel of monoclonal antibodies (MAbs) to the ectodomain of HKU1 spike protein. They did not cross-react with S proteins of any other CoV tested. Most of the HKU1 spike MAbs recognized epitopes in the C domain between amino acids 535 and 673, indicating that this region is immunodominant. Two of the MAbs blocked HKU1 virus infection of primary human tracheal-bronchial epithelial (HTBE) cells. Preincubation of HTBE cells with a truncated HKU1 S protein that includes the C domain blocked infection with HKU1 virus, but preincubation of cells with truncated S protein containing only the NTD did not block infection. These data suggest that the receptor-binding domain (RBD) of HKU1 spike protein is located in the C domain, where the spike proteins of α-CoVs and β-CoVs in groups B and C bind to their specific receptor proteins. Thus, two β-CoVs in group A, HKU1 and murine CoV, have evolved to use different regions of their spike glycoproteins to recognize their respective receptor proteins.IMPORTANCEMouse hepatitis virus, a β-CoV in group A, uses the galectin-like NTD in its spike protein to bind its receptor protein, while HCoV-OC43, another β-CoV in group A, uses the NTD to bind to its sialic-acid containing receptor. In marked contrast, the NTD of the spike glycoprotein of human respiratory β-CoV HKU1, which is also in group A, does not bind sugar. In this study, we showed that for the spike protein of HKU1, the purified C domain, downstream of the NTD, could block HKU1 virus infection of human respiratory epithelial cells, and that several monoclonal antibodies that mapped to the C domain neutralized virus infectivity. Thus, the receptor-binding domain of HKU1 spike glycoprotein is located in the C domain. Surprisingly, two β-CoVs in group A, mouse hepatitis virus and HKU1, have evolved to use different regions of their spike glycoproteins to recognize their respective receptors.

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