Molecular modeling and mutagenesis studies of the N-terminal domains of galectin-3: evidence for participation with the C-terminal carbohydrate recognition domain in oligosaccharide binding

A model structure (Henrick,K., Bawumia,S., Barboni,E.A.M., Mehul,B. and Hughes, R.C. (1998) Glycobiology:, 8, 45-57) of the carbohydrate recognition domain (CRD, amino acid residues 114-245) of hamster galectin-3 has been extended to include N-terminal domain amino acid residues 91-113 containing one of the nine proline-rich motifs present in full-length hamster galectin-3. The modeling predicts two configurations of the N-terminal tail: in one the tail turns toward the first (SI) and last (S12) beta-strands of the CRD and lies at the apolar dimer interface observed for galectins -1 and -2. In the second folding arrangement the N-terminal tail lies across the carbohydrate-binding pocket of the CRD where it could participate in sugar-binding: in particular tyrosine 102 and adjacent residues may interact with the partly solvent exposed nonreducing N-acetylgalactosamine and fucose substituents of the A-blood group structure GalNAcalpha1,3 [Fucalpha1,2]Galbeta1,4GlcNAc-R. Binding studies using surface plasmon resonance of a recombinant fragment Delta1-93 protein containing residues 94-245 of hamster galectin-3 and a collagenase-derived fragment Delta1-103 containing residues 104-245, as well as alanine mutagenesis of residues 101-105 in Delta1-93 protein, support the prediction that Tyr102 and adjacent residues make significant contributions to oligosaccharide binding.