Figure 1.
Elucidation of the HBGA-binding pocket and the genetic relatedness of HBGA-binding interfaces among different genotypes of human noroviruses.
The top four panels show structures of noroviruses at different levels: (from left to right) an electron microscopy image of noroviruses, a single virus-like particle (VLP), a P dimer with indication of the carbohydrate-binding interface (colored region), and the crystal structure of the HBGA-binding interface. The dashed square in each left panel is enlarged in the right panel. The HBGA is indicated by a ring-shaped trisaccharide. The middle panel shows the crystal structures of the HBGA-binding interface of the prototype Norwalk virus (GI.1, left) and the aligned sequences of the receptor-binding interface of eight GI genotypes (right). The bottom panel shows the crystal structures of the HBGA-binding interface of strain VA387 (GII.4, left) and the aligned sequences of the receptor-binding interface of 17 GII genotypes (right). The HBGA-binding interface can be divided into three sites representing the bottom (green) and walls (orange and red) of the binding pocket. The same color schemes are used in the sequence alignments to highlight the conserved amino acid residues of the three sites. Partially adapted, with permission, from [8].
Figure 2.
Schematic interactions and relationships among different human noroviruses with a complete product of human HBGA.
Representative strains of different genotypes in the two major genogroups (GI and GII) of human noroviruses are shown according to their target saccharides. Arrows indicate interactions between individual noroviruses and specific residues of human HBGAs. Dashed lines indicate a weaker interaction. The five circles in different colors represent the five saccharide residues of a complete product of an H-related HBGA (H, A, B, Leb, or Ley). The curved dashed arrows indicate two major binding groups, the A/B/H (blue) and the Lewis/H (black) binding groups, according to their target residues on human HBGAs. The binding specificity and affinity of these norovirus strains were determined in [30].