Figure 5.

Potential multivalency of Man-9. Each of the five Man residues that can theoretically bind in the monosaccharide-binding site of PAL are highlighted in red. In the crystal structures only Man^B is observed to bind in the monosaccharide-binding site. Theoretically, each of the three arms could interact with a different lectin molecule via Man^D1, Man^D2, Man^D3, and Man^C. The other four Mans are excluded from the monosaccharide-binding site for steric reasons. Even with the binding mode observed via Man^C as shown in Figures 1 to 3, the D3 arm remains free to interact with a second lectin molecule. Still, only a 1:1 stoichiometry is observed in solution and a unique binding mode in the crystal.