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

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Abstract
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) β-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 GalNAcα1,3 [Fucα1,2]Galβ1,4GlcNAc-R. Binding studies using surface plasmon resonance of a recombinant fragmentΔ1–93 protein containing residues 94–245 of hamster galectin-3 and a collagenase-derived fragment Δ1–103 containing residues 104–245, as well as alanine mutagenesis of residues 101–105 in Δ1–93 protein, support the prediction that Tyr102 and adjacent residues make significant contributions to oligosaccharide binding.

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