NMR solution studies of hamster galectin-3 and electron microscopic visualization of surface-adsorbed complexes: evidence for interactions between the N- and C-terminal domains.

Galectin-3, a β-galactoside binding protein, contains a C-terminal carbohydrate recognition domain (CRD) and an N-terminal domain that includes several repeats of a proline-tyrosine-glycine-rich motif. Earlier work based on a crystal structure of human galectin-3 CRD, and modeling and mutagenesis studies of the closely homologous hamster galectin-3, suggested that N-terminal tail residues immediately preceding the CRD might interfere with the canonical subunit interaction site of dimeric galectin-1 and -2, explaining the monomeric status of galectin-3 in solution. Here we describe high-resolution NMR studies of hamster galectin-3 (residues 1−245) and several of its fragments. The results indicate that the recombinant N-terminal fragment Δ126−245 (residues 1−125) is an unfolded, extended structure. However, in the intact galectin-3 and fragment Δ1−93 (residues 94−245), N-terminal domain residues lying between positions 94 and 113 have significantly reduced mobility values compared with those expected for b...