Noroviruses, an important cause of acute gastroenteritis, have been found to recognize human histo-blood group antigens (HBGAs) as receptors. Four strain-specific binding patterns to HBGAs have been described in our previous report. In this study, we have extended the binding patterns to seven based on 14 noroviruses examined. The oligosaccharide-based assays revealed additional epitopes that were not detected by the saliva-

Noroviruses are one of the major causes of nonbacterial gastroenteritis epidemics in humans. Recent studies on norovirus receptors show that different noroviruses recognize different human histo-blood group antigens (HBGAs), and eight receptor binding patterns of noroviruses have been identified. The P domain of the norovirus capsids is directly involved in this recognition. To determine the precise locations and receptor binding modes of HBGA carbohydrates on the viral capsids, a recombinant P protein of a GII-4 strain norovirus, VA387, was cocrystallized with synthetic type A or B trisaccharides. Based on complex crystal structures observed at a 2.0-Å resolution, we demonstrated that the receptor binding site lies at the outermost end of the P domain and forms an extensive hydrogen-bonding network with the saccharide ligand. The A and B trisaccharides display similar binding modes, and the common fucose ring plays a key role in this interaction. The extensive interface between the two protomers in a P dimer also plays a crucial role in the formation of the receptor binding interface.

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Norovirus is the most important cause of nonbacterial acute gastroenteritis. We have shown previously that the isolated P domain containing the hinge forms a dimer and binds to histo-blood group antigen (HBGA) receptors with a low affinity (M. Tan, R. S. Hegde, and X. Jiang, J. Virol. 78:6233-6242, 2004). Here, we reported that the P domain of VA387 without the hinge forms a small particle with a significantly increased receptor binding affinity. An end-linked oligopeptide containing one or more cysteines promoted P-particle formation by forming intermolecular disulfide bridges. The binding sensitivity of the P particle to HBGAs was enhanced >700-fold compared to the P dimer, which was comparable to that of virus-like particles. The binding specificity of the P particle was further confirmed by strong binding to the Caco-2 cells, a human colon carcinoma cell line. This binding enhancement was observed in the P particles of both norovirus GI and GII strains. The P particle is estimated to contain 12 P dimers, in which the P2 subdomain builds up the outer layer, while the P1 subdomain forms the internal core. Taken together, our data indicate that the P domain is involved not only in dimerization but also in polymerization of the protein during the capsid assembling. The enhanced receptor binding of the P particle reflects the intrinsic feature of the viral capsid. The easy production of the P particle and its strong binding to HBGAs suggest that the P particle is useful in studying pathogenesis and morphogenesis of norovirus and candidates for antiviral or vaccine development.Norovirus, previously called Norwalk-like virus or small round structured virus, is the most important viral pathogen of epidemic acute gastroenteritis in both developed and developing countries (9, 10). Recent advances in understanding of norovirus-host interaction and the viral receptors have opened a new approach to study the host range and pathogenesis (18, 31). Noroviruses recognize human histo-blood group antigens (HBGAs) as receptors, which are complex carbohydrates present on red blood cells and mucosal epithelium or as free antigens in biological fluids, such as saliva, milk, and intestinal contents (25,29). The recognition of HBGAs by noroviruses is strain specific, and eight distinct receptor-binding patterns have been identified (13,14,16,17,19,26). The linkage of norovirus binding to HBGAs with clinical infection has been demonstrated in human volunteer studies. In the case of the prototype Norwalk virus (NV), for example, individuals of nonsecretors were naturally resistant to NV infection following the challenge (23). It seems logical to predict that each virus strain of the other binding patterns has its own host range defined by host blood type, although a recent human volunteer study of another norovirus, the Snow Mountain virus, did not reveal clear association between infection and host blood type (22).Norovirus belongs to the family Caliciviridae. It contains a positive-strand, polyadenylated RNA genome of ϳ7.7 kb that i...