A SINGLE AMINO-ACID RESIDUE CAN DETERMINE THE LIGAND SPECIFICITY OF E-SELECTIN

E-selectin (ELAM-1) is a member of the selectin family of cellular adh esion molecules. This family of proteins possesses an amino-terminal C a2+-dependent lectin or carbohydrate recognition domain that is essent ial for Ligand binding. A known E-selectin ligand is the carbohydrate antigen, sialyl Lewis(x) (sLe(x)) (Neu5Ac alpha 2-3Gal beta 1-4(Fuc al pha-1-3)GlcNAc). We have developed a model of E-selectin binding to th e sLe(x) tetrasaccharide, (Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3) GlcNAc), using the NMR-determined, E-selectin-bound solution conformat ion of sLe(x) (Cooke, R. M., Hale, R. S., Lister, S. G., Shah, G., and Weir, M. P. (1994) Biochemistry 33, 10591-10596) together with the x- ray crystallographic structures of E-selectin (Graves, B. J., Crowther , R. L., Chandran, C., Rumberger, J. B., Li, s., Huang, K.-S., Presky, D. H., Familletti, P. C., Wolitzky, B. A., and Burns, D. K. (1994) Na ture 367, 532-538) (ligand unbound) and a related C-type animal lectin , the mannose-binding protein (Weis, W. I., Drickamer, K., and Hendric kson, A. (1992) Nature 360, 127-134) (ligand bound). Analysis of this model indicated that the alteration of one E-selectin amino acid, alan ine 77, to a lysine residue might shift binding specificity from sLe(x ) to mannose. The results presented here show that an E-selectin mutan t protein possessing this change displays preferential binding to mann ose containing oligosaccharides and that further mutagenesis of this m annose-binding selectin confers galactose recognition in a predictable manner. These mutagenesis data support the presented model of the det ailed interactions between E-selectin and the sLe(x) oligosaccharide.