Structure and Function of a Ganglioside Receptor for Porcine Rotavirus

A ganglioside fraction isolated from pooled intestines from newborn to 4-week-old piglets, which we previously partially characterized and showed to specifically inhibit the binding of porcine rotavirus (OSU strain) to host cells (M. D. Rolsma, H. B. Gelberg, and M. S. Kuhlenschmidt, J. Virol. 68:258–268, 1994), was further purified and found to contain two major monosialogangliosides. Each ganglioside was purified to apparent homogeneity, and their carbohydrate structure was examined by high-pH anion-exchange chromatography coupled with pulsed amperometric detection and fast atom bombardment mass spectroscopy. Both gangliosides possessed a sialyllactose oligosaccharide moiety characteristic of GM(3) gangliosides. Compositional analyses indicated that each ganglioside was composed of sialic acid, galactose, glucose, and sphingosine in approximately a 1:1:1:1 molar ratio. Each ganglioside differed, however, in the type of sialic acid residue it contained. An N-glycolylneuraminic acid (NeuGc) moiety was found in the more polar porcine GM(3), whereas the less polar GM(3) species contained N-acetylneuraminic acid (NeuAc). Both NeuGcGM(3) and NeuAcGM(3) displayed dose-dependent inhibition of virus binding to host cells. NeuGcGM(3) was approximately two to three times more effective than NeuAcGM(3) in blocking virus binding. Inhibition of binding occurred with as little as 400 pmol of NeuGcGM(3)/50 ng of virus (∼2 × 10(7) virions) and 2 × 10(6) cells/ml. Fifty percent inhibition of binding was achieved with 0.64 and 1.5 μM NeuGcGM(3) and NeuAcGM(3), respectively. The free oligosaccharides 3′- and 6′-sialyllactose inhibited binding 50% at millimolar concentrations, which were nearly 1,000 times the concentration of intact gangliosides required for the same degree of inhibition. Direct binding of infectious, triple-layer rotavirus particles, but not noninfectious, double-layered rotavirus particles, to NeuGcGM(3) and NeuAcGM(3) was demonstrated by using a thin-layer chromatographic overlay assay. NeuGcGM(3) and NeuAcGM(3) inhibited virus infectivity of MA-104 cells by 50% at concentrations of 3.97 and 9.84 μM, respectively. NeuGcGM(3) (700 nmol/g [dry weight] of intestine) was found to be the predominant enterocyte ganglioside (comprising 75% of the total lipid-bound sialic acid) in neonatal piglets, followed by NeuAcGM(3) (200 nmol/g [dry weight] of intestine). NeuGcGM(3) and NeuAcGM(3) together comprised nearly 100% of the lipid-bound sialic acid in the neonatal intestine, but their quantities rapidly diminished during the first 5 weeks of life. These data support the hypothesis that porcine NeuGcGM(3) and NeuAcGM(3) are physiologically relevant receptors for porcine rotavirus (OSU strain). Further support for this hypothesis was obtained from virus binding studies using mutant or neuraminidase-treated cell lines. Lec-2 cells, a mutant clone of CHO cells characterized by a 90% reduction in sialyllation of its glycoconjugates, bound less than 5% of the virus compared to control cell binding. In contrast, Lec-1 cells, a mutant CHO clone characterized by a deficiency in glycosylation of N-linked oligosaccharides, still bound rotavirus. Furthermore, exogenous addition of NeuGcGM(3) to the Lec-2 mutant cells restored their ability to bind rotavirus in amounts equivalent to that of their parent (CHO) cell line. In the virus-permissive MA-104 cell line, NeuGcGM(3) was also able to partially restore rotavirus infectivity in neuraminidase-treated cells. These data suggest that gangliosides play a major role in recognition of host cells by porcine rotavirus (OSU strain).