Abstract

The spike proteins of a number of coronaviruses are able to bind to sialic acids present on the cell surface. The importance of this sialic acid binding ability during infection is, however, quite different. We compared the spike protein of transmissible gastroenteritis virus (TGEV) and the spike protein of infectious bronchitis virus (IBV). Whereas sialic acid is the only receptor determinant known so far for IBV, TGEV requires interaction with its receptor aminopeptidase N to initiate infection of cells. Binding tests with soluble spike proteins carrying an IgG Fc-tag revealed pronounced differences between these two viral proteins. Binding of the IBV spike protein to host cells was in all experiments sialic acid dependent, whereas the soluble TGEV spike showed binding to APN but had no detectable sialic acid binding activity. Our results underline the different ways in which binding to sialoglycoconjugates is mediated by coronavirus spike proteins.

Highlights

  • Transmissible gastroenteritis virus (TGEV) is a porcine alphacoronavirus and is a major pathogen for piglets unless they are protected by antibodies

  • The S1 portions of the genes of TGEV spike and infectious bronchitis virus (IBV) spike proteins were successfully cloned into the vector pCG1Fc where the open reading frames were in frame with the human IgG Fc tag

  • Soluble TGEV Spike protein binds to cells expressing APN

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Summary

Introduction

Transmissible gastroenteritis virus (TGEV) is a porcine alphacoronavirus and is a major pathogen for piglets unless they are protected by antibodies. For TGEV, two binding properties of the S-protein have been described, the binding to the cellular receptor porcine aminopeptidase N and a sialic acid binding activity, which is important for the enteropathogenicity for the virus [1, 2]. A naturally occurring variant virus of TGEV, the porcine respiratory coronavirus (PRCoV), lacks this sialic acid binding property due to a deletion in the N-terminal portion of the S1 subunit and is not enteropathogenic. Betacoronavirus, viruses like BCoV and HCoV-OC43 bind to 9-O acetylated sialic acid residues and have an additional membrane protein, the hemagglutinin-esterase, which has receptor-destroying activity. In this study we compared the sialic acid binding properties of the spike proteins of TGEV and IBV using soluble spike proteins containing an IgG Fc-tag

Cloning and expression of soluble spike proteins
Soluble TGEV Spike protein binds to cells expressing APN
Experimental Section
Cloning of soluble proteins
Preparation of soluble proteins
Binding tests
FACS analysis
Conclusions
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