The platelet receptor for von Willebrand factor (VWF), glycoprotein (GP) Ib-IX, mediates initial platelet adhesion and activation. It is known that the cytoplasmic domain of GPIb is phosphorylated at Ser by cAMPdependent protein kinase (PKA). To understand the physiological role of GPIb phosphorylation, a GPIb-IX mutant replacing Ser of GPIb with alanine (S166A) and a deletion mutant lacking re...

The platelet glycoprotein Ib (GpIb) complex is composed of four polypeptides: the disulfide-linked GpIb alpha and GpIb beta and the noncovalently associated GpIX and GpV. GpIb alpha contains binding sites for von Willebrand factor and for thrombin and mediates platelet adhesion to the subendothelium under conditions of high shear stress. We have previously shown the presence of GpIb alpha and G...

atomic resolution structural information is X-ray crystallography, a technique accounting for 88% of structures deposited in the Protein Data Bank. Unfortunately, this technique requires milligram amounts of purified protein , which has to subsequently be induced to form crystals. Both protein production and crystallization can be difficult tasks particularly for membrane-bound, multidomain and...

Platelet glycoprotein Ib (GpIb), a receptor for von Willebrand's factor (vWF), was studied by way of fluorescence flow cytometry. Using a sandwich staining technique, GpIb was identified by a monoclonal antibody (6D1) directed against an epitope close to the vWF binding site. Platelets from normal individuals were symmetrically distributed with respect to GpIb content. Treatment of washed plate...

Sera of 12 patients with quinine/quinidine-induced thrombocytopenia showed drug-dependent antibody binding to glycoprotein (GP) Ib-IX complex. The reaction with GPIb-IX complex of 11 of these 12 sera was strongly inhibited by the complex-specific monoclonal antibodies (MoAbs) AK1 and SZ1. The exception was a quinine-induced serum designated BU. The reaction of the six quinidine-induced sera was...

Thrombin-induced cellular response in platelets not only requires protease-activated receptors (PARs), but also involves another thrombin receptor, the glycoprotein Ib-IX complex (GPIb-IX). It remains controversial how thrombin binding to GPIb-IX stimulates platelet responses. It was proposed that GPIb-IX serves as a dock that facilitates thrombin cleavage of protease-activated receptors, but t...

Current antithrombotic drugs have an adverse effect on bleeding, highlighting the need for new molecular targets for developing antithrombotic drugs that minimally affect hemostasis. Here we show that LIMK1(-/-) mice have defective arterial thrombosis in vivo but do not differ from wild-type mice with respect to bleeding time. LIMK1(-/-) mice show a selective defect in platelet activation induc...

Platelet membrane glycoprotein (GP) Ib contains receptors for von Willebrand factor and thrombin. Its proteolytic fragment, glycocalicin, circulates in normal plasma. In this study, storage of platelet concentrates for 5 d resulted in a 221% increase in plasma glycocalicin (1.3 times the total amount of glycocalicin present on the surface of all platelets), an 8% overall increase in platelet su...

Thrombin decreases the platelet surface expression of the glycoprotein (GP) Ib-IX complex. To determine whether this effect is reversible, flow cytometric studies were performed with GPIb-IX-specific monoclonal antibodies. In both whole blood and washed platelet systems, incubation of platelets with thrombin or a combination of adenosine diphosphate and epinephrine resulted in a maximal decreas...