Partial identification of the epitope on D-dimer for monoclonal antibody, DD-3B6/22

This study provides new information about the recognition site on fibrin for DD-3B6/22, a monoclonal antibody used in the diagnosis of thrombotic disease and proposed as a delivery agent for radioisotopes to visualize thrombi in situ. Preliminary chemical modification and proteolytic digestion of D-dimer revealed key residues in the interaction of D-dimer with its diagnostic antibody DD-3B6/22. Following the initial survey, thermolysin was used to produce digestion fragments for more specific sequence analysis. The gamma-polypeptide chain of D-dimer was confirmed as a recognition site for the antibody, with the residues S86RK88 being implicated in binding, and a second, novel site of antibody interaction was identified on the alpha-polypeptide as D105NTYNR110. Based on evidence from this study and from a previous investigation of the DD-3B6/22 binding site on D-dimer (Devine and Greenberg), a model for the DD-3B6/22 binding site is proposed to comprise regions from parts, at or near the N-terminus, of at least two different subunits: one region on the alpha-polypeptide chain of one D monomer and another region on the gamma-polypeptide chain of an adjacent D monomer. The model is discussed in the context of the predicted secondary and tertiary structure of D-dimer.