Abstract
Guinea fowl coronavirus (GfCoV) causes fulminating enteritis that can result in a daily death rate of 20% in guinea fowl flocks. Here, we studied GfCoV diversity and evaluated its phenotypic consequences. Over the period of 2014 to 2016, affected guinea fowl flocks were sampled in France, and avian coronavirus presence was confirmed by PCR on intestinal content and immunohistochemistry of intestinal tissue. Sequencing revealed 89% amino acid identity between the viral attachment protein S1 of GfCoV/2014 and that of the previously identified GfCoV/2011. To study the receptor interactions as a determinant for tropism and pathogenicity, recombinant S1 proteins were produced and analyzed by glycan and tissue arrays. Glycan array analysis revealed that, in addition to the previously elucidated biantennary di-N-acetyllactosamine (diLacNAc) receptor, viral attachment S1 proteins from GfCoV/2014 and GfCoV/2011 can bind to glycans capped with alpha-2,6-linked sialic acids. Interestingly, recombinant GfCoV/2014 S1 has an increased affinity for these glycans compared to that of GfCoV/2011 S1, which was in agreement with the increased avidity of GfCoV/2014 S1 for gastrointestinal tract tissues. Enzymatic removal of receptors from tissues before application of spike proteins confirmed the specificity of S1 tissue binding. Overall, we demonstrate that diversity in GfCoV S1 proteins results in differences in glycan and tissue binding properties.IMPORTANCE Avian coronaviruses cause major global problems in the poultry industry. As causative agents of huge economic losses, the detection and understanding of the molecular determinants of viral tropism are of ultimate importance. Here, we set out to study those parameters and obtained in-depth insight into the virus-host interactions of guinea fowl coronavirus (GfCoV). Our data indicate that diversity in GfCoV viral attachment proteins results in differences in degrees of affinity for glycan receptors, as well as altered avidity for intestinal tract tissues, which might have consequences for GfCoV tissue tropism and pathogenesis in guinea fowls.
Highlights
Guinea fowl coronavirus (GfCoV) causes fulminating enteritis that can result in a daily death rate of 20% in guinea fowl flocks
Fulminating disease in guinea flocks continued to be reported after the initial outbreak of GfCoV infection in 2011 [6]
Viral protein expression using antibodies against the M protein of avian coronaviruses was observed in all duodena and in four out of the seven lower intestinal tracts by immunohistochemistry (IHC) (Fig. 1, white arrowheads)
Summary
Guinea fowl coronavirus (GfCoV) causes fulminating enteritis that can result in a daily death rate of 20% in guinea fowl flocks. To study the receptor interactions as a determinant for tropism and pathogenicity, recombinant S1 proteins were produced and analyzed by glycan and tissue arrays. Our data indicate that diversity in GfCoV viral attachment proteins results in differences in degrees of affinity for glycan receptors, as well as altered avidity for intestinal tract tissues, which might have consequences for GfCoV tissue tropism and pathogenesis in guinea fowls. Studies using recombinant IBV S1 and/or RBD proteins have demonstrated that the viral tropism is reflected by tissue binding of such proteins [11]. In contrast to IBV, GfCoV and TCoV target the epithelial cells of the gastrointestinal tract [4, 6], and recombinant protein binding of their S1 proteins reflects this viral tropism, with predominant staining of epithelial cells of the small intestine [4]. Susceptible cell lines have not yet been identified, inoculation of embryonated guinea fowl eggs did not result in GfCoV production (data not shown), and specific-pathogen-free (SPF) guinea fowls are not available for experimental infection
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