The murine
monoclonal antibody BR55-2 is directed against the
tumor-associated
antigen Lewis
Y oligosaccharide. The Lewis Y core
antigen is a difucosylated structure consisting of four
hexose units. Analysis of binding profiles of lactoseries isomeric structures by BR55-2 suggest that the binding
epitope includes the OH-4 and OH-3 groups of the beta-
D-galactose unit, the 6-CH3 groups of the two
fucose units and the N-acetyl group of the subterminal beta-D-
N-acetylglucosamine (beta DGlcNAc). To elucidate the molecular recognition properties of BR55-2 for the Y
antigen, BR55-2 was cloned, sequenced and its three-dimensional structure was examined by molecular modeling. The crystal structure of BR96, another anti-Lewis Y antibody, solved in complex with a nonoate methyl
ester Lewis Y tetrasaccharide, and the
lectin IV
protein in complex with a
Lewis b tetrasaccharide core were used as a guide to probe the molecular basis for BR55-2
antigen recognition and specificity. Our modeling study shows that BR55-2 shares similar recognition features for the difucosylated type 2 lactoseries Lewis Y structure observed in the BR96-sugar complex. We observe that a major source of specificity for the Lewis Y structure by anti-Y
antibodies emanates from interaction with the beta-D-
N-acetylglucosamine residue and the nature of the structures extended at the reducing site of the fucosylated lactosoamine.