About the Lectin

The lectin from the seeds of Dioclea grandiflora (DGL) is a Man/Glc- specific tetrameric protein with physical and saccharide-binding properties reported to be similar to that of the jack bean lectin concanavalin A (ConA). Unlike other plant lectins, both DGL and Con A bind with high
affinity to the core trimannoside moiety, 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside, which is present in all asparagines-linked carbohydrates. ¹ Unlike Con A, DGL does not bind to biantennary complex carbohydrates. This was confirmed by showing that biantennary complex glycopeptides do not bind to a DGL-Sepharose affinity column. Unlike ConA, DGL does not show enhanced affinity for a large N-linked oligomannose carbohydrate
(Man9 glycopeptide) relative to the trimannoside. Thus, DGL and ConA share similar epitope recognition of the core trimannoside moiety. However they exhibit differences in their fine specificities for larger N-linked oligomannose and complex carbohydrates. ¹ The overall structure of the DGL complex is similar to the structure of the ConA-trimannoside
complex. ² The location and conformation of the bound trimannoside as well assists hydrogen-bonding interactions in both complexes are nearly identical. However, differences
exist in the location of two loops outside of the respective binding sites containing residues 114-124 and 222-227. The latter residues affect the location of a network of hydrogenbonded
water molecules that interact with the trisaccharide. Differences in the arrangement of ordered water molecules in the binding site and/or protein conformational differences outside of the binding site may account for the differences in the thermodynamics of binding of the two lectins to deoxy analogs of the trimannoside. Molecular modeling studies suggest how DGL discriminates against binding the biantennary complex carbohydrate relative to ConA. ³

C. bonariensis, C. floribunda, D. rostrata, and D. violacea, like D. grandiflora, show substantially reduced affinities for a biantennary complex carbohydrate with terminal GlcNAc residues, while C. brasiliensis, D.guianensis, and D. virgata, like ConA, exhibit affinities
for the oligosaccharide comparable with that of the trimannoside.Thermodynamic data obtained by ITC indicate different energetic mechanisms of binding of the above two groups of lectins to the complex carbohydrate. The ability of the lectins to induce histamine release from rat peritoneal mast cells is shown to correlate with the relative affinities of the proteins for the biantennary carbohydrate. ⁴

REFERENCES

1. Gupta, D., et al. (1996) European J. Biochem. 242: 320-326.
2. Naismith,J.H., et al. (1996) J.Biol.Chem. 271: 972-976.
3. Rozwarski, D.A., et al. (1998) J. Biol Chem. 273: 32818-32825
4. Dam, K., Cavada, B.S., et al. (1998) J. Biol Chem 273:12082-12088