Fig 1.
Structures and nomenclatures of the oligosaccharides in this article.
Lewis-y blood group determinants H-tetra-BGA, B-penta-BGA, A-penta-BGA and the related human milk oligosaccharide A-penta-HMO. All of these have type-2 core structures. Note that H-tetra-HMO and A-penta-HMO were referred to as H-tetra and A-penta in our previous publications [27, 29]. Carbohydrate symbols follow the nomenclature of the Consortium for Functional Glycomics (Nomenclature Committee, Consortium for Functional Glycomics (functionalglycomics.org/static/consortium/Nomenclature.shtml); d-galactose (Gal)–yellow circle, N-acetylgalactosamine (GalNAc)–yellow square, d-glucose (Glc)–blue circle, N-acetylglucosamine (GlcNAc)–blue square, l-fucose (Fuc)–red triangle.
Table 1.
Data collection and refinement statistics.
Fig 2.
Blood group antigen binding to the cholera toxin.
(A) X-ray structure of cCTB in complex with A-penta-BGA (PDB ID: 5ELD); side and top views. The B-pentamer is colored by subunit, and the ligands are shown in stick representation. Blood group determinants are bound to the lateral side of the toxin (modeled into four of the five secondary binding sites), and galactose to the primary binding site (in three of the sites), facing the cell membrane. (B-G) Close-up views of the blood group antigen binding sites. Oligosaccharide residues are labeled in italics, amino acid residues in bold, and residues from neighboring subunits are indicated with a hash (#). (B-C) Interactions of the blood group A determinant with cCTB and ET CTB. Biotype-specific residues are highlighted in orange and green sticks. Water molecules are shown as red spheres, and hydrogen bonds are depicted as red dashed lines. (D-E) Electron density. σA-weighted Fo − Fc maps (green mesh; contoured at 3.0σ) are shown for the blood group A determinant and a human milk oligosaccharide. The maps were generated before insertion of the ligands. Circles indicate special features: the GlcNAc’s N-acetyl group, and the less-defined electron density for GalNAc in A-penta-BGA. (F-G) Interaction of the blood group H determinant with cCTB and ET CTB (two orientations). Yellow residues mark the reducing-end GlcNAc, α and β anomers are labeled. Water molecules are depicted as red spheres, hydrogen bonds represented by red dashed lines. In B, C, F and G, only those H-bonds are shown that have favorable angles, maximum bond lengths of 3.5 Å and that are conserved in all binding sites.
Fig 3.
Representative SPR sensorgrams and affinity plots.
SPR experiments were performed in triplicates, with cCTB or ET CTB coupled to the sensor chip and using blood group determinants or A-penta-HMO as analytes, as indicated in the panel legends. The final KD values are shown with standard deviations. The KD value for ET CTB + A-penta-BGA could not be calculated since it did not reach saturation upon addition of 30 mM ligand. The experiments with A-penta-HMO were done at a separate occasion; therefore the RU-axes are not comparable. Details are provided in the Materials and Methods section.
Fig 4.
Molecular model of cholera blood group dependence.
V. cholerae burrows through the mucus layer, aided by its flagellum and mucinases. After colonization, it produces the cholera toxin. CT’s interaction with the host cells depends on the person’s blood group and secretor status. In secretors, blood group antigens are expressed on mucins and intestinal epithelial cells. H-antigens (characteristic of blood group O) can bind the toxin in two orientations. They bind the toxin more strongly than A-antigens and therefore retain the toxin, increasing the risk of cellular uptake. CT has a lower affinity to A-antigens, and is therefore more easily ejected by the peristaltic movement of the intestine. This protects secretors with blood group A from severe disease, while blood group O individuals suffer more serious symptoms.