Affinities of recombinant norovirus P dimers for human blood group antigens

Noroviruses (NoVs), the major cause of viral acute gastroenteritis, recognize histo-blood group antigens (HBGAs) as receptors or attachment factors. To gain a deeper understanding of the interplay between NoVs and their hosts, the affinities of recombinant P dimers (P-2's) of a GII.4 NoV (VA387) to a library of 41 soluble analogs of HBGAs were measured using the direct electrospray ionization mass spectrometry assay. The HBGAs contained the A, B, H and Lewis epitopes, with variable sizes (2-6 residues) and different types (1-6). The results reveal that the P-2's exhibit a broad specificity for the HBGAs and bind to all of the oligosaccharides tested. Overall, the affinities are relatively low, ranging from 400 to 3000 M-1 and are influenced by the chain type: 3 > 1 approximate to 2 approximate to 4 approximate to 5 approximate to 6 for H antigens; 6 > 1 approximate to 3 approximate to 4 approximate to 5 > 2 for A antigens; 3 > 1 approximate to 4 approximate to 5 approximate to 6 > 2 for B antigens, but not by chain length. The highest-affinity ligands are B type 3 (3000 +/- 300 M-1) and A type 6 (2350 +/- 60 M-1). While the higher affinity to the type 3 H antigen was previously observed, preferential binding to the types 6 and 3 antigens with A and B epitopes, respectively, has not been previously reported. A truncated P domain dimer (lacking the C-terminal arginine cluster) exhibits similar binding. The central-binding motifs in the HBGAs were identified by molecular-docking simulations.