Identification and location on syndecan-1 core protein of the epitopes of B-B2 and B-B4 monoclonal antibodies.

Using a phage display peptide library, we characterized the epitope of two monoclonal antibodies reacting with syndecan-1: B-B2 and B-B4. The identified epitopes QDIT, for B-B2, and LPEV, for B-B4, were found to align with residues 36-39 and 90-93 of the mature protein, respectively. In contrast to B-B4, the B-B2 epitope is close to a potential glycosaminoglycan attachment site. Since syndecan-1 is heavily glycosylated and post-translational modifications are cell type specific, these results might explain the differences observed in the reactivity pattern of B-B2 and B-B4 and suggest that these monoclonal antibodies are useful probes to study cell surface exposed syndecan-1.