Figure 9.

Stereo view of the loops that form the saccharide binding site in legume lectins. The binding site regions of Gal-specific peanut lectin (1BZW; bound to galactose) and of Man/Glc-specific concanavalin A (5CNA; bound to mannose) are superposed on each other. The loops A, B, and C superpose very well. However, large differences are seen in the specificity-determining loop D region (Sharma and Surolia 1997; labeled D and D′ corresponding to 1BZW and 5CNA, respectively). The orientation of the bound saccharide relative to the aromatic amino acid is also different: mannose interacts with the aromatic residue through its C5-H and C6-H atoms, whereas galactose interacts through its C3-H, C4-H, C5-H, and C6-H atoms.