HEMOPHILIC BINDING-PROPERTIES OF GALECTIN-3 - INVOLVEMENT OF THE CARBOHYDRATE-RECOGNITION DOMAIN

Galectin-3, an animal lectin specific for P-galactosides, is composed of three different domains. The N-terminal half of the molecule (N dom ain) consists of a short N-terminal segment followed by glycine-, prol ine-, and tyrosine-rich tandem repeats. The C-terminal domain (C domai n) harbors the carbohydrate recognition domain homologous to other mem bers of the galectin family of lectins. Galectin-3 aggregates in solut ion, and participation of the N domain of the molecule in this process has already been demonstrated. Using a solid-phase radioligand bindin g assay, which allows the direct analysis of galectin-3 self-associati on, here we provide evidence that the carbohydrate recognition domain of the lectin is involved in carbohydrate-dependent hemophilic interac tions: (a) Radiolabeled galectin-3 binds to immobilized galectin-3, an d the addition of unlabeled galectin-3 in solution increases the rate of binding of radiolabeled lectin; (b) binding of radiolabeled galecti n-3 to immobilized galectin-3 is inhibited by the C domain; (c) bindin g of radiolabeled galectin-3 to immobilized galectin-3 or the C domain is inhibited by lactose but not by sucrose; and (d) the radiolabeled C domain does not bind to immobilized C domain, Taken together, these data suggest that in addition to the N domain, the hemophilic interact ions of galectin-3 are mediated by the C domain.