ROLE OF THE GLYCOPROTEIN IB-BINDING A1 REPEAT AND THE RGD SEQUENCE INPLATELET-ADHESION TO HUMAN RECOMBINANT VON-WILLEBRAND-FACTOR

To assess the relative importance of the glycoprotein (GP) Ib binding domain and the RGDS binding site in platelet adhesion to isolated von Willebrand factor (vWF) and to collagen preincubated with vWF, we dele ted the A1 domain yielding Delta A1-vWF and introduced an aspartate-to -glycine substitution in the RGDS sequence by site-directed mutagenesi s (RGGS-vWF). Recombinant Delta A1-vWF and RGGS-vWF, purified from tra nsfected baby hamster kidney cells, were compared with recombinant wil d-type vWF (WT-vWF) in platelet adhesion under static and flow conditi ons, Purified mutants were coated on glass or on a collagen type III s urface and exposed to circulating blood in a perfusion system. Platele t adhesion under static condition, under flow conditions, and in vWF-d ependent adhesion to collagen has an absolute requirement for GPIb-vWF interaction. The GPIIb/IIIa-vWF interaction is required for adhesion to coated vWF under flow conditions. Under static condition and vWF-de pendent adhesion to collagen, platelet adhesion to RGGS-vWF is similar as to WT-vWF, but platelet spreading and aggregation are abolished. ( C) 1995 by The American Society of Hematology.