Comparative Epitope Mapping with Saturation Transfer Difference NMR of Sialyl Lewis~a Compounds and Derivatives Bound to a Monoclonal Antibody

摘要

The monoclonal antibody GSLA-2 recognizes the sialyl Lewis~a(sLe~a)epitope,which has an increased occurrence on mucin type glycoproteins of patients with colorectal carcinoma.GSLA-2 is therefore used in tumor diagnosis.To advance the understanding of this highly specific molecular recognition reaction,we have analyzed the binding epitope of sLe~a at atomic resolution using saturation transfer difference NMR.To compare,the binding epitopes of sialyl Lewis~x(sLe~x)and of four synthetic derivatives of sLe~a were explored.Surface plasmon resonance experiments furnished thermodynamic and kinetic data.It is observed that all pyranose rings of sLe~a are in contact with the protein surface,with the neuramic acid residue receiving the largest fraction of saturation transfer.In contrast,sLe~x binds very weakly,though specifically to GSLA-2,with a different binding epitope.This study provides a comprehensive picture of the recognition sLe~a and explains the exquisite specificity of the antibody.