Galectins are a growing family of animal lectins with common consensus sequences that bind b-Gal and LacNac residues. There are at present 14 members of the galectin family; however, certain galectins possess different structures as well as biol. properties. Galectin-1 is a dimer of two homologous carbohydrate recognition domains (CRDs) and possesses apoptotic and proinvasive activities. Galectin-3 consists of a C-terminal CRD and an N-terminal nonlectin domain implicated in the oligomerization of the protein and is often assocd. with antiapoptotic activity. Because many cellular oligosaccharide receptors are multivalent, it is important to characterize the interactions of multivalent carbohydrates with galectins-1 and -3. In the present study, binding of bovine heart galectin-1 and recombinant murine galectin-3 to a series of synthetic analogs contg. two LacNAc residues sepd. by a varying no. of methylene groups, as well as biantennary analogs possessing two LacNAc residues, were examd. using isothermal titrn. microcalorimetry (ITC) and hemagglutination inhibition measurements. The thermodn. of binding of the multivalent carbohydrates to the C-terminal CRD domain of galectin-3 was also investigated. ITC results showed that each bivalent analog bound by both LacNAc residues to the two galectins. However, galectin-1 shows a lack of enhanced affinity for the bivalent straight chain and branched chain analogs, whereas galectin-3 shows enhanced affinity for only lacto-N-hexaose, a naturally occurring branched chain carbohydrate. The CRD domain of galectin-3 was shown to possess similar thermodn. binding properties as the intact mol. The results of this study have important implications for the design of carbohydrate inhibitors of the two galectins. [on SciFinder (R)]