Sialic acid binding properties of soluble coronavirus spike (S1) proteins: differences between infectious bronchitis virus and transmissible gastroenteritis virus - PubMed (original) (raw)

Sialic acid binding properties of soluble coronavirus spike (S1) proteins: differences between infectious bronchitis virus and transmissible gastroenteritis virus

Katarina Shahwan et al. Viruses. 2013.

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.

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Figures

Figure 1

Figure 1

Schematic drawing of the soluble spike proteins. S1 subunits are fused c-terminally to the human IgG Fc portion.

Figure 2

Figure 2

ST cells and IPI-21 cells, both of porcine origin were used for binding tests with soluble S transmissible gastroenteritis virus (TGEV)-S protein. Binding was evaluated immunofluorescence microscopy. Cells were either not treated (A, D) or pretreated with 100 mU of neuraminidase (B, E). Binding of soluble spikes was detectable on both neuraminidase treated and not treated cells. Control cells were incubated only with the secondary anti human FITC labeled antibody (C,F)

Figure 3

Figure 3

BHK-21 cells and HEK 293T cells were transfected with a plasmid for APN expression (A, B, D, E) and used for binding tests with soluble TGEV spike proteins. Binding was only detectable when porcine APN was expressed (A,B,D,E) and no binding was observed on cells transfected only with empty vector (C,F). A neuraminidase pre-treatment revealed an enhanced binding of the TGEV spike to the cells (B,E).

Figure 4

Figure 4

FACS analysis of soluble TGEV spikes bound to BHK-21 cells (A) and ST-cells (B). Binding was only detectable on BHK-21 cells expressing APN. A neuraminidase pre-treatment of the cells revealed an increased binding on both cell lines.

Figure 5

Figure 5

Binding test of soluble TGEV spike protein on cryosections of porcine jejunum: cryosections were either pretreated (+NA) or not treated (-NA) with 300 mU neuraminidase prior to binding of soluble spikes. The control cryosections were incubated only with the fluorescence dye (CY3) labeled secondary antibody. No decrease in the binding of TGEV spikes was observed after neuraminidase treatment.

Figure 6

Figure 6

Sialic acid dependent binding of soluble IBV spike proteins to IBV-susceptible chicken cells: primary chicken embryo kidney cells (CKC) and cryosections of chicken trachea have been treated (+NA) or not treated (-NA) with 200 mU neuraminidase prior to the binding of soluble spike proteins. The binding is clearly reduced in the desialylated samples.

References

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