Molecular recognition of the Lewis Y antigen by monoclonal antibodies

The murine monoclonal antibody BR55-2 is directed against thetumor-associated antigen Lewis Y oligosaccharide. The LewisY core antigen is a difucosylated structure consisting of fourhexose units. Analysis of binding profiles of lactoseries isomericstructures by BR55–2 suggest that the binding epitopeincludes the OH-4 and OH-3 groups of the ß-D-galactoseunit, the 6-CH₃ groups of the two fucose units and the N-acetylgroup of the subterminal ß-D-N-acetylglucosamine (ßDGlcNAc).To elucidate the molecular recognition properties of BR55–2for the Y antigen, BR55–2 was cloned, sequenced and itsthree-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 tetrasaccharidecore were used as a guide to probe the molecular basis for BR55–2antigen recognition and specificity. Our modeling study showsthat BR55–2 shares similar recognition features for thedifucosylated type 2 lactoseries Lewis Y structure observedin the BR96-sugar complex. We observe that a major source ofspecificity for the Lewis Y structure by anti-Y antibodies emanatesfrom interaction with the ß-D-N-acetylglucosamineresidue and the nature of the structures extended at the reducingsite of the fucosylated lactosoamine.