A consensus tetrapeptide selected by phage display adopts the conformation of a dominant discontinuous epitope of a monoclonal Anti-VWF antibody that inhibits the von Willebrand factor-collagen interaction

Monoclonal antibody (mAb) 82D6A3 is an anti-von Willebrand factor (VWF) mAb directed against the A3-domain of VWF that inhibits the VWF binding to fibrillar collagens type I and III in vitro and in vivo. To identify the discontinuous epitope of this mAb, we used phage display, mutant analysis, and peptide modeling. All 82D6A3-binding phages displayed peptides containing the consensus sequence SPWR that could be aligned with P981W982 in the VWF A3-domain. Next, the binding of mAb 82D6A3 to 27 Ala mutants with mutations in the A3-domain of VWF revealed that amino acids Arg(963), Pro(981), Asp(1009), Arg(1016), Ser(1020), Met(1022), and His(1023) are part of the epitope of mAb 82D6A3. Inspection of residues Ser(1020), Arg(1016), Pro(981), and Trp(982) in the three-dimensional structure of the A3-domain demonstrated that these residues are close together in space, pointing out that the structure of the SPWR consensus sequence might mimic this discontinuous epitope. Modeling of a cyclic 6-mer peptide containing the consensus sequence and superposition of its three-dimensional structure onto the VWF A3-domain demonstrated that the Ser and Arg in the peptide matched the Ser(1020) and Arg(1016) in the A3-domain. The Pro residue of the peptide served as a spacer, and the side chain of the Trp pointed in the direction of Trp(982). In conclusion, to our knowledge, this is the first report where a modeled peptide containing a consensus sequence could be fitted onto the three-dimensional structure of the antigen, indicating that it might adopt the conformation of the discontinuous epitope.