Glycan Shield and Fusion Activation of a Deltacoronavirus Spike Glycoprotein Fine-Tuned for Enteric Infections

Author:

Xiong Xiaoli1,Tortorici M. Alejandra23,Snijder Joost1,Yoshioka Craig4,Walls Alexandra C.1,Li Wentao5,McGuire Andrew T.6,Rey Félix A.23,Bosch Berend-Jan5,Veesler David1

Affiliation:

1. Department of Biochemistry, University of Washington, Seattle, Washington, USA

2. Institut Pasteur, Unité de Virologie Structurale, Paris, France

3. CNRS UMR 3569 Virologie, Paris, France

4. Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon, USA

5. Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands

6. Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA

Abstract

ABSTRACT Coronaviruses recently emerged as major human pathogens causing outbreaks of severe acute respiratory syndrome and Middle East respiratory syndrome. They utilize the spike (S) glycoprotein anchored in the viral envelope to mediate host attachment and fusion of the viral and cellular membranes to initiate infection. The S protein is a major determinant of the zoonotic potential of coronaviruses and is also the main target of the host humoral immune response. We report here the 3.5-Å-resolution cryo-electron microscopy structure of the S glycoprotein trimer from the pathogenic porcine deltacoronavirus (PDCoV), which belongs to the recently identified Deltacoronavirus genus. Structural and glycoproteomics data indicate that the glycans of PDCoV S are topologically conserved compared with the human respiratory coronavirus NL63 S, resulting in similar surface areas being shielded from neutralizing antibodies and implying that both viruses are under comparable immune pressure in their respective hosts. The structure further reveals a shortened S 2 ′ activation loop, containing a reduced number of basic amino acids, which participates in rendering the spike largely protease resistant. This property distinguishes PDCoV S from recently characterized betacoronavirus S proteins and suggests that the S protein of enterotropic PDCoV has evolved to tolerate the protease-rich environment of the small intestine and to fine-tune its fusion activation to avoid premature triggering and reduction of infectivity. IMPORTANCE Coronaviruses use transmembrane S glycoprotein trimers to promote host attachment and fusion of the viral and cellular membranes. We determined a near-atomic-resolution cryo-electron microscopy structure of the S ectodomain trimer from the pathogenic PDCoV, which is responsible for diarrhea in piglets and has had devastating consequences for the swine industry worldwide. Structural and glycoproteomics data reveal that PDCoV S is decorated with 78 N-linked glycans obstructing the protein surface to limit accessibility to neutralizing antibodies in a way reminiscent of what has recently been described for a human respiratory coronavirus. PDCoV S is largely protease resistant, which distinguishes it from most other characterized coronavirus S glycoproteins and suggests that enteric coronaviruses have evolved to fine-tune fusion activation in the protease-rich environment of the small intestine of infected hosts.

Funder

HHS | NIH | National Institute of General Medical Sciences

Pew Charitable Trusts

Publisher

American Society for Microbiology

Subject

Virology,Insect Science,Immunology,Microbiology

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