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 beta-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 Delta 126--245 (residues 1--125) is an unfolded, extended structure. However, in the intact galectin-3 and fragment Delta 1--93 (residues 94--245), N-terminal domain residues lying between positions 94 and 113 have significantly reduced mobility values compared with those expected for bulk N-terminal tail residues, consistent with an interaction of this segment with the CRD domain. In contrast to the monomeric status of galectin-3 (and fragment Delta 1--93) in solution, electron microscopy of negatively stained and rotary shadowed samples of hamster galectin-3 as well as the CRD fragment Delta 1--103 (residues 104--245) show the presence of a significant proportion (up to 30%) of oligomers. Similar imaging of the N-terminal tail fragment Delta 126--245 reveals the presence of fibrils formed by intermolecular interactions between extended polypeptide subunits. Oligomerization of substratum-adsorbed galectin-3, through N- and C-terminal domain interactions, could be relevant to the positive cooperativity observed in binding of the lectin to immobilized multiglycosylated proteins such as laminin.
Birdsall
B
B
Molecular Structure Division, National Institute for Medical Research, Mill Hill, London, NW7 1AA, UK.
Feeney
J
J
Burdett
I D
ID
Bawumia
S
S
Barboni
E A
EA
Hughes
R C
RC
D000327:Adsorption; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000943:Antigens, Differentiation / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D002241:Carbohydrates / Q000737:chemistry; D006224:Cricetinae; D037502:Galectin 3; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017434:Protein Structure, Tertiary / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000648:ultrastructure; D020449:Repetitive Sequences, Amino Acid; D012996:Solutions
D000943:Antigens, Differentiation; D002241:Carbohydrates; D037502:Galectin 3; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D012996:Solutions