Shielding of the A1 Domain by the D′D3 Domains of von Willebrand Factor Modulates Its Interaction with Platelet Glycoprotein Ib-IX-V

• Published in: The Journal of biological chemistry 2006-02, Vol.281 (8), p.4699-4707
• Main Authors: Ulrichts, Hans, Udvardy, Miklós, Lenting, Peter J., Pareyn, Inge, Vandeputte, Nele, Vanhoorelbeke, Karen, Deckmyn, Hans
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M513314200

Soluble von Willebrand factor (VWF) has a low affinity for platelet glycoprotein (GP) Ibα and needs immobilization and/or high shear stress to enable binding of its A1 domain to the receptor. The previously described anti-VWF monoclonal antibody 1C1E7 enhances VWF/GPIbα binding and recognizes an epitope in the amino acids 764–1035 region in the N-terminal D′D3 domains. In this study we demonstrated that the D′D3 region negatively modulates the VWF/GPIb-IX-V interaction; (i) deletion of the D′D3 region in VWF augmented binding to GPIbα, suggesting an inhibitory role for this region, (ii) the isolated D′D3 region inhibited the GPIbα interaction of a VWF deletion mutant lacking this region, indicating that intramolecular interactions limit the accessibility of the A1 domain, (iii) using a panel of anti-VWF monoclonal antibodies, we next showed that the D′D3 region is in close proximity with the A1 domain in soluble VWF but not when VWF was immobilized; (iv) destroying the epitope of 1C1E7 resulted in a mutant VWF with an increased affinity for GPIbα. Our results support a model of domain translocation in VWF that allows interaction with GPIbα. The suggested shielding interaction of the A1 domain by the D′D3 region then becomes disrupted by VWF immobilization.