Abstract
Sapovirus, a member of the Caliciviridae family, is an important cause of acute gastroenteritis in humans and pigs. Currently, the porcine sapovirus (PSaV) Cowden strain remains the only cultivable member of the Sapovirus genus. While some caliciviruses are known to utilize carbohydrate receptors for entry and infection, a functional receptor for sapovirus is unknown. To characterize the functional receptor of the Cowden strain of PSaV, we undertook a comprehensive series of protein-ligand biochemical assays in mock and PSaV-infected cell culture and/or piglet intestinal tissue sections. PSaV revealed neither hemagglutination activity with red blood cells from any species nor binding activity to synthetic histo-blood group antigens, indicating that PSaV does not use histo-blood group antigens as receptors. Attachment and infection of PSaV were markedly blocked by sialic acid and Vibrio cholerae neuraminidase (NA), suggesting a role for α2,3-linked, α2,6-linked or α2,8-linked sialic acid in virus attachment. However, viral attachment and infection were only partially inhibited by treatment of cells with sialidase S (SS) or Maackia amurensis lectin (MAL), both specific for α2,3-linked sialic acid, or Sambucus nigra lectin (SNL), specific for α2,6-linked sialic acid. These results indicated that PSaV recognizes both α2,3- and α2,6-linked sialic acids for viral attachment and infection. Treatment of cells with proteases or with benzyl 4-O-β-D-galactopyranosyl-β-D-glucopyranoside (benzylGalNAc), which inhibits O-linked glycosylation, also reduced virus binding and infection, whereas inhibition of glycolipd synthesis or N-linked glycosylation had no such effect on virus binding or infection. These data suggest PSaV binds to cellular receptors that consist of α2,3- and α2,6-linked sialic acids on glycoproteins attached via O-linked glycosylation.
Highlights
Caliciviruses are small (27–40 nm), nonenveloped, icosahedral viruses that possess a single-strand, plussense genomic RNA of 7–8 kb [1]
Binding of porcine sapovirus (PSaV) Cowden strain was reduced to 12% of the levels observed in mock treated cells with 1 mM NaIO4, and to 2% in cells treated with 5 mM NaIO4 (Fig. 1B)
A similar degree of inhibition of binding and infection was observed in Feline calicivirus (FCV) F9 strain-infected Crandall-Reese feline kidney (CRFK) cells that were pretreated with NaIO4 (Fig.1B and 1D)
Summary
Caliciviruses (family Caliciviridae) are small (27–40 nm), nonenveloped, icosahedral viruses that possess a single-strand, plussense genomic RNA of 7–8 kb [1]. Caliciviruses are important veterinary and human pathogens which are associated with a broad spectrum of diseases in their respective hosts. Feline calicivirus (FCV), a member of the genus Vesivirus, causes respiratory disease in cats [3,4]. Caliciviruses in the genera Norovirus and Sapovirus are important acute gastroenteritis pathogens in humans and animals [5,6]. Human noroviruses cause at least 1.1 million episodes and 218,000 deaths in developing nations as well as approximately 900,000 cases of pediatric gastroenteritis in industrialized nations [7]. No fully permissive cell culture system currently exists for the enteric caliciviruses associated with gastroenteritis in humans, hampering the study of viral pathogenesis and immunity of these ubiquitous pathogens [1]
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