THE ANIMAL LECTIN GALECTIN-3 INTERACTS WITH BACTERIAL LIPOPOLYSACCHARIDES VIA 2 INDEPENDENT SITES

Galectin-3 is a beta-galactoside binding protein expressed by activate d macrophages, epithelial cells, and certain other cell types. Galecti n-3 has a C-terminal carbohydrate binding domain, an N-terminal part c onsisting of a proline- and glycine-rich repetitive domain, and a smal l N-terminal domain. Two independent LPS binding sites on galectin-3 w ere demonstrated by binding of biotinylated LPS to immobilized recombi nant galectin-3. One appears to be the carbohydrate binding site in th e C-terminal domain that confers binding of LPS from Klebsiella pneumo niae that has a p-galactoside-containing polysaccharide chain, This bi nding is best demonstrated using galectin-3 immunocaptured by a mAb to the N-terminal part (M3/38) and is inhibited by lactose. In contrast, Salmonella minnesota R7 LPS (Rd mutant), which is devoid of beta-gala ctosides, appears to bind to a site within the N-terminal part of gale ctin-3. This interaction is best demonstrated using galectin-3 directl y immobilized in wells, and it is inhibited by the Ab M3/38, but not b y lactose. Binding inhibition by polymyxin B and the profile of inhibi tion by a panel of LPSs with different amounts of the inner and outer cores present indicate that this second binding site recognizes the li pid A/inner core region of LPSs.