Lectin cross-linking interactions with multivalent carbohydrates.

The present findings provide a molecular basis for a new paradigm of specificity in multivalent carbohydrate-lectin interactions, namely the formation of type 2 homogeneous cross-linked lattices between multivalent carbohydrates and lectins. The present x-ray data demonstrate that the cross-linked complexes formed between a series of structurally related divalent carbohydrates and a single tetravalent lectin (SBA) are distinct and due to crystal packing interactions. These results thus provide a molecular basis for the formation of homogeneous type 2 cross-linked complexes between lectins and multivalent carbohydrates and glycoconjugates. These findings are also relevant to the observations that lectin-carbohydrate cross-linking interactions are involved in cellular recognition and signal transduction processes. For example, activated human T-cells undergo apoptosis due to binding and cross-linking of specific glycoprotein receptors by galectin-1 (Pace et al., 1999). Confocal microscopy shows that the galectin cross-linked glycoprotein receptors form homogeneous aggregates from a population of previously dispersed molecules on the surface of the cells. The crystal structures of the four SBA/pentasaccharide complexes thus repesent models for lectin-carbohydrate clustering in vivo.