Effect of deletion of the A1 domain of von Willebrand factor on its binding to heparin, collagen and platelets in the presence of ristocetin

Abstract

In order to study the functional importance of the collagen, heparin and glycoprotein‐Ib‐binding domain, we deleted the A1 domain of von Willebrand factor (vWF), corresponding to residues 478–716, by oligonucleotide‐directed mutagenesis. The resulting ΔA1‐vWF cDNA was expressed in COS‐1 monkey kidney cells and compared to wild‐type vWF. The higher‐molecular‐mass multimers were decreased in ΔA1 recombinant von Willebrand factor (ΔA1‐rvWF) compared to plasma vWF and rvWF. The reactivity of ΔA1‐rvWF and rvWF with monoclonal antibodies directed against the collagen‐binding domain (residues 969–992), the vessel‐wall‐binding domain, and the binding site for glycoprotein IIb‐III a on platelets was identical. The interaction with vWF of the monoclonal antibody directed against the glycoprotein Ib binding domain was abolished for ΔA1‐rvWF, and similar to plasma vWF for rvWF. The binding of factor VIII to ΔA1‐rvWF and rvWF was similar. ΔA1‐rvWF and rvWF bound similarly to collagen, but the binding of ΔA1‐rvWF to heparin and to platelets in the presence of ristocetin were abolished. These data indicate that the heparin‐binding site in the A1 domain is essential. There is no second binding domain for glycoprotein Ib outside the A1 domain. The collagen‐binding domain in the A1 domain is either not active or its action can be compensated by the second collagen‐binding domain. Copyright © 1991, Wiley Blackwell. All rights reserved