Recognition mechanism of galectin-4 for cholesterol 3-sulfate

Galectin-4 binds to glycosphingolipids carrying 3-O-sulfated Gal residues, and it co-localizes on the cell surface of human colonic adenocarcinoma cells with glycosphingolipids carrying SO3--->3Gal beta 1-->3(GalNAc) residues (Ideo, H., Seko, A., and Yamashita, K. (2005) J. Biol. Chem. 280, 4730-4737). In the present study, it was found that galectin-4 also binds to cholesterol 3-sulfate, which has no beta-galactoside moiety. This characteristic of galectin-4 is unique within the galectin family. The site-directed mutated galectin-4-R45A had diminished binding ability toward cholesterol 3-sulfate, suggesting that Arg(45) of galectin-4 is indispensable for cholesterol 3-sulfate recognition. Gel filtration and chemical cross-linking experiments revealed that some galectin-4 exists as dimers, and this multivalency seemed to enhance its avidity for cholesterol 3-sulfate binding. Cholesterol 3-sulfate and sulfatide co-existed with galectin-4 in detergent-insoluble fractions of porcine esophagus and intestine, respectively. These results suggested that not only sulfated glycosphingolipids but also cholesterol 3-sulfate are endogenous ligands for galectin-4 in vivo.