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Open Access Research

The sialic acid binding activity of the S protein facilitates infection by porcine transmissible gastroenteritis coronavirus

Christel Schwegmann-Weßels1*, Sandra Bauer1, Christine Winter12, Luis Enjuanes3, Hubert Laude4 and Georg Herrler1

Author Affiliations

1 Institute for Virology, University of Veterinary Medicine Hannover, Bünteweg 17, 30559 Hannover, Germany

2 Clinic for Poultry, University of Veterinary Medicine Hannover, Bünteweg 17, 30559 Hannover, Germany

3 Centro Nacional de Biotecnología, CSIC, Department of Molecular and Cell Biology, Campus Universitario de Cantoblanco, Darwin 3, 28049 Madrid, Spain

4 Institut National de la Recherche Agronomique, Unité de Virologie Immunologie Moléculaires (VIM), Domaine de Vilvert, Jouy-en-Josas, 78350, France

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Virology Journal 2011, 8:435  doi:10.1186/1743-422X-8-435

Published: 12 September 2011

Abstract

Background

Transmissible gastroenteritis virus (TGEV) has a sialic acid binding activity that is believed to be important for enteropathogenicity, but that has so far appeared to be dispensable for infection of cultured cells. The aims of this study were to determine the effect of sialic acid binding for the infection of cultured cells under unfavorable conditions, and comparison of TGEV strains and mutants, as well as the avian coronavirus IBV concerning their dependence on the sialic acid binding activity.

Methods

The infectivity of different viruses was analyzed by a plaque assay after adsorption times of 5, 20, and 60 min. Prior to infection, cultured cells were either treated with neuraminidase to deplete sialic acids from the cell surface, or mock-treated. In a second approach, pre-treatment of the virus with porcine intestinal mucin was performed, followed by the plaque assay after a 5 min adsorption time. A student's t-test was used to verify the significance of the results.

Results

Desialylation of cells only had a minor effect on the infection by TGEV strain Purdue 46 when an adsorption period of 60 min was allowed for initiation of infection. However, when the adsorption time was reduced to 5 min the infectivity on desialylated cells decreased by more than 60%. A TGEV PUR46 mutant (HAD3) deficient in sialic acid binding showed a 77% lower titer than the parental virus after a 5 min adsorption time. After an adsorption time of 60 min the titer of HAD3 was 58% lower than that of TGEV PUR46. Another TGEV strain, TGEV Miller, and IBV Beaudette showed a reduction in infectivity after neuraminidase treatment of the cultured cells irrespective of the virion adsorption time.

Conclusions

Our results suggest that the sialic acid binding activity facilitates the infection by TGEV under unfavorable environmental conditions. The dependence on the sialic acid binding activity for an efficient infection differs in the analyzed TGEV strains.

Keywords:
coronavirus S protein; sialic acid binding activity; TGEV; IBV; cultured cells