Human Coronavirus HKU1 Spike Protein Uses O-Acetylated Sialic Acid as an Attachment Receptor Determinant and Employs Hemagglutinin-Esterase Protein as a Receptor-Destroying Enzyme

By Xingchuan Huang, Wenjuan Dong, A. Milewska, A. Golda, Yonghe Qi, Q. Zhu, W. Marasco, Ralph S. Baric, Amy C. Sims, K. Pyrć and 2 more. 2015

236 citations recorded by the source corpus.

ABSTRACT Human coronavirus (hCoV) HKU1 is one of six hCoVs identified to date and the only one with an unidentified cellular receptor. hCoV-HKU1 encodes a hemagglutinin-esterase (HE) protein that is unique to the group a betacoronaviruses (group 2a). The function of HKU1-HE remains largely undetermined. In this study, we examined binding of the S1 domain of hCoV-HKU1 spike to a panel of cells and found that the S1 could specifically bind on the cell surface of a human rhabdomyosarcoma cell line, RD. Pretreatment of RD cells with neuraminidase (NA) and trypsin greatly reduced the binding, suggesting that the binding was mediated by sialic acids on glycoproteins. However, unlike other group 2a CoVs, e.g., hCoV-OC43, for which 9-O-acetylated sialic acid (9-O-Ac-Sia) serves as a receptor determinant, HKU1-S1 bound with neither 9-O-Ac-Sia-containing glycoprotein(s) nor rat and mouse erythrocytes. Nonetheless, the HKU1-HE was similar to OC43-HE, also possessed sialate-O-acetylesterase activity, and acted as a receptor-destroying enzyme (RDE) capable of eliminating the binding of HKU1-S1 to RD cells, whereas the O-acetylesterase-inactive HKU1-HE mutant lost this capacity. Using primary human ciliated airway epithelial (HAE) cell cultures, the only in vitro replication model for hCoV-HKU1 infection, we confirmed that pretreatment of HAE cells with HE but not the enzymatically inactive mutant blocked hCoV-HKU1 infection. These results demonstrate that hCoV-HKU1 exploits O-Ac-Sia as a cellular attachment receptor determinant to initiate the infection of host cells and that its HE protein possesses the corresponding sialate-O-acetylesterase RDE activity. IMPORTANCE Human coronaviruses (hCoV) are important human respiratory pathogens. Among the six hCoVs identified to date, only hCoV-HKU1 has no defined cellular receptor. It is also unclear whether hemagglutinin-esterase (HE) protein plays a role in viral entry. In this study, we found that, similarly to other members of the group 2a CoVs, sialic acid moieties on glycoproteins are critical receptor determinants for the hCoV-HKU1 infection. Interestingly, the virus seems to employ a type of sialic acid different from those employed by other group 2a CoVs. In addition, we determined that the HKU1-HE protein is an O-acetylesterase and acts as a receptor-destroying enzyme (RDE) for hCoV-HKU1. This is the first study to demonstrate that hCoV-HKU1 uses certain types of O-acetylated sialic acid residues on glycoproteins to initiate the infection of host cells and that the HKU1-HE protein possesses sialate-O-acetylesterase RDE activity.

Subfields: Infectious Diseases, Molecular Biology

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Citations in the corpus

• Prefusion structure of a human coronavirus spike protein (2016, background): “acids on host cells, and these glycans were required for efficient infection of primary human airway epithelial cultures 9 .”
• Coronavirus Infections in Children Including COVID-19 (2020, background): “[173] [174] [175] [176] However, rapid mutation of CoVs poses a potential problem, which might be diminished by using several monoclonal antibodies targeting different epitopes.”
• New insights on the antiviral effects of chloroquine against coronavirus: what to expect for COVID-19? (2020, background): “[96] Huang X , Dong W , Milewska A , Golda A , Qi Y , Zhu QK , et al.”
• Crystal structure of the receptor binding domain of the spike glycoprotein of human betacoronavirus HKU1 (2017, background): “These results indicate that the function and overall conformation of the purified 1A-S310-677aa protein was nearly intact.”
• Identification of sialic acid-binding function for the Middle East respiratory syndrome coronavirus spike glycoprotein (2017, unknown): “Comparative sequence analysis identified MERS-CoV as a clade C Betacor-onavirus (order Nidovirales, family Coronaviridae , subfamily Coronavirinae , genus Betacoronavirus ) (2, 3), closely related to bat CoVs HKU4 and HKU5 and to a hedgehog CoV (4, 5).”
• Molecular Evolution of Human Coronavirus Genomes (2016, unknown): “Unlike the influenza virus C enzyme, CoV HEs lack membrane-fusion activity and are accessory to the spike protein by serving primarily as receptor-destroying enzymes (RDE) – that is, they aid viral detachment from carbohydrates present on infected cells [29,30].”
• Cryo-EM structures of MERS-CoV and SARS-CoV spike glycoproteins reveal the dynamic receptor binding domains (2017, unknown): “However, the glycan-binding site on the top of MERS-CoV NTD is occupied by a short helix and the N-linked glycan on that helix, and thus NTD in this conformation maybe unable to attach the cell surface by recognizing certain sugar molecules, unlike BCoV and HKU1 (refs 25,26).”
• Human coronaviruses OC43 and HKU1 bind to 9-O-acetylated sialic acids via a conserved receptor-binding site in spike protein domain A (2019, background): “However, HKU1, like the β1CoVs, uses 9-O-Ac-sialoglycans for attachment and the binding to these receptors is essential for infection (14).”
• Title: Mosaic nanoparticles elicit cross-reactive immune responses to zoonotic coronaviruses in mice (2020, unknown): “The RBDs of human coronaviruses SARS-CoV-2, SARS-CoV, HCoV-NL63, and related animal coronaviruses (WIV1 and SCH014) use angiotensin-converting enzyme 2 (ACE2) as their host receptor (1, 8, 9), while other coronaviruses use receptors such as dipeptidyl peptidase 4 (10) or sialic acids (11, 12).”
• Immunogenicity and structures of a rationally designed prefusion MERS-CoV spike antigen (2017, background): “For HCoV-HKU1, a protein receptor has not yet been identified, but the S1 subunit has been shown to bind O-acetylated sialic acids (57).”