title: Role of the carboxyl-terminal lectin domain in self-association of galectin-3.
abstract: Galectin-3 is a member of a large family of beta-galactoside-binding animal lectins and is composed of a carboxyl-terminal lectin domain connected to an amino-terminal nonlectin part. Previous experimental results suggest that, when bound to multivalent glycoconjugates, galectin-3 self-associates through intermolecular interactions involving the amino-terminal domain. In this study, we obtained evidence suggesting that the protein self-associates in the absence of its saccharide ligands, in a manner that is dependent on the carboxyl-terminal domain. This mode of self-association is inhibitable by the lectin's saccharide ligands. Specifically, recombinant human galectin-3 was found to bind to galectin-3C (the carboxyl-terminal domain fragment) conjugated to Sepharose 4B and the binding was inhibitable by lactose. In addition, biotinylated galectin-3 bound to galectin-3 immobilized on plastic surfaces and the binding could also be inhibited by various saccharide ligands of the lectin. A mutant with a tryptophan to leucine replacement in the carboxyl-terminal domain, which exhibited diminished carbohydrate-binding activity, did not bind to galectin-3C-Sepharose 4B. Furthermore, galectin-3C formed covalent homodimers when it was treated with a chemical cross-linker and the dimer formation was completely inhibited by lactose. Therefore, galectin-3 can self-associate through intermolecular interactions involving both the amino- and the carboxyl-terminal domains and the relative contribution of each depends on whether the lectin is bound to its saccharide ligands.
authors.affiliation: Division of Allergy, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
authors.forename: R Y
authors.initials: RY
authors.lastname: Yang
authors.forename: P N
authors.initials: PN
authors.lastname: Hill
authors.forename: D K
authors.initials: DK
authors.lastname: Hsu
authors.forename: F T
authors.initials: FT
authors.lastname: Liu
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001667:Binding, Competitive; D003432:Cross-Linking Reagents; D037502:Galectin 3; D006367:HeLa Cells; D006801:Humans; D007073:Immunoglobulin E / Q000378:metabolism; D019169:Jurkat Cells; D007785:Lactose / Q000494:pharmacology; D037102:Lectins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007930:Leucine / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D012685:Sepharose / Q000378:metabolism; D014364:Tryptophan / Q000235:genetics
chemical_list: D000943:Antigens, Differentiation; D003432:Cross-Linking Reagents; D037502:Galectin 3; D037102:Lectins; D010446:Peptide Fragments; D007073:Immunoglobulin E; D014364:Tryptophan; D012685:Sepharose; D007930:Leucine; D007785:Lactose