Recombinant vWF type 2A mutants R834Q and R834W show a defect in mediating platelet adhesion to collagen, independent of enhanced sensitivity to a plasma protease.

Type 2A von Willebrand Disease (vWD) is characterized by the absence of high molecular weight von Willebrand factor (VWF) multimers in plasma which is caused by enhanced extracellular proteolysis or defective intracellular transport. We identified in vWD type 2A patients two mutations in the A2 domain at position 834 in which arginine (R) was substituted for glutamine (R834Q) or tryptophan (R834W). We reproduced these mutations in vWF cDNA and expressed the recombinant proteins in furin cDNA containing baby hamster kidney (fur-BHK) cells.

Relative importance of the glycoprotein Ib-binding domain and the RGD sequence of von Willebrand factor for its interaction with endothelial cells.

Endothelial cell adhesion to von Willebrand Factor is mainly mediated through an interaction between the alpha vbeta3 integrin and the RGD sequence of von Willebrand factor (vWF). To define the potential involvement of glycoprotein Ib alpha (GPIb alpha) as an endothelial vWF receptor, we compared cell adhesion to three recombinant vWF, the wild-type (WT-rvWF) and two mutants, RGGS-rvWF (D1746G), defective for binding to platelet alphaIIb beta3, and deltaA1-rvWF with a deletion between amino-acids 478 and 716, which does not bind to platelet GPIb alpha. Adhesion of human umbilical vein endothelial cells to purified vWF recombinants was measured by automatized cell counting using an image analyzer.

von Willebrand factor without the A2 domain is resistant to proteolysis.

von Willebrand factor (vWF) is a complex multimeric plasma glycoprotein, that plays a critical role in the mediation of platelet adhesion to the damaged vascular wall, and functions as a carrier protein for factor VIII. vWF has a domain structure consisting of repeated A, B, C, and D domains. The A1 domain is involved in binding to the platelet receptor glycoprotein (GP) Ib, and the A3 domain has a binding site for collagen.

Functional studies on platelet adhesion with recombinant von Willebrand factor type 2B mutants R543Q and R543W under conditions of flow.

Type 2B von Willebrand disease (vWD) is characterized by the absence of the very high molecular weight von Willebrand factor (vWF) multimers from plasma, which is caused by spontaneous binding to platelet receptor glycoprotein Ib (GPIb). We studied two mutations in the A1 domain at position 543 in which arginine (R) was replaced by glutamine (Q) or tryptophan (W), respectively. Both mutations were previously identified in vWD type 2B patients.

Proteolytic cleavage of recombinant type 2A von Willebrand factor mutants R834W and R834Q: inhibition by doxycycline and by monoclonal antibody VP-1.

The susceptibility of recombinant type 2A von Willebrand factor (vWF) to a recently identified plasma metalloproteinase and the potential application of proteolysis inhibition in the treatment of the disease were investigated. Two recombinant type 2A vWF mutants, R834W and R834Q, were spontaneously cleaved by the partially purified plasma proteinase to smaller forms. When treated with guanidine HCI, both the wild-type and the R834W mutant vWF exhibited a biphasic change in proteolytic susceptibility, reaching the same maximum cleavage at 1.

A3 domain is essential for interaction of von Willebrand factor with collagen type III.

von Willebrand factor (vWF) mediates platelet adhesion at sites of vascular damage. It acts as a bridge between receptors on platelets and collagens present in the connective tissue. Two collagen binding sites have been identified on the A1 and A3 domain of the vWF subunit.

Platelet adhesion to multimeric and dimeric von Willebrand factor and to collagen type III preincubated with von Willebrand factor.

As part of a systematic study of platelet interaction with adhesive proteins under flow conditions, we studied platelet adhesion to multimeric and dimeric von Willebrand factor (vWF) coated to glass. vWF-dependent adhesion to collagen type III was studied for comparison. Adhesion to glass-coated vWF and vWF-mediated adhesion to collagen type III were in many respects similar.

Requirements of von Willebrand factor to protect factor VIII from inactivation by activated protein C.

The interaction of factor VIII with von Willebrand factor (vWF) was investigated on a quantitative and qualitative level. Binding characteristics were determined using a solid phase binding assay and protection of factor VIII by vWF from inactivation by activated protein C (aPC) was studied using three different assays. Deletion mutants of vWF, a 31-kD N-terminal monomeric tryptic fragment of vWF that contained the factor VIII binding site (T31) and multimers of vWF of different size were compared with vWF purified from plasma.

On the role of von Willebrand factor in promoting platelet adhesion to fibrin in flowing blood.

Platelet adhesion to fibrin at high shear rates depends on both the glycoprotein (GP) IIb:IIIa complex and a secondary interaction between GPIb and von Willebrand factor (vWF). This alternative link between platelets and vWF in promoting platelet adhesion to fibrin has been examined in flowing whole blood with a rectangular perfusion chamber. Optimal adhesion required both platelets and vWF, as shown by the following observations.

Role of the glycoprotein Ib-binding A1 repeat and the RGD sequence in platelet 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 deleted the A1 domain yielding delta A1-vWF and introduced an aspartate-to-glycine substitution in the RGDS sequence by site-directed mutagenesis (RGGS-vWF). Recombinant delta A1-vWF and RGGS-vWF, purified from transfected baby hamster kidney cells, were compared with recombinant wild-type vWF (WT-vWF) in platelet adhesion under static and flow conditions. Purified mutants were coated on glass or on a collagen type III surface and exposed to circulating blood in a perfusion system.

Efficient immunocastration of male piglets by immunoneutralization of GnRH using a new GnRH-like peptide.

Active immunization to immunomodulate regulatory processes suffers from the disadvantage that the antigen is usually 'self' and therefore poorly immunogenic. This has been well illustrated by the long-standing experience with immunocastration vaccines targeting GnRH, a ten amino acid peptide. Not all animals vaccinated with these vaccines are equally affected, even after multiple vaccinations.

Outer membrane PhoE protein of Escherichia coli as a carrier for foreign antigenic determinants: immunogenicity of epitopes of foot-and-mouth disease virus.

Outer membrane protein PhoE of Escherichia coli was used for the expression of antigenic determinants of foot-and-mouth disease virus. Five hybrid PhoE proteins were constructed containing different combinations of two antigenic determinants of VP1 protein of the virus. The hybrid proteins were expressed in two E.

Manipulation of antipeptide immune response by varying the coupling of the peptide with the carrier protein.

Antibodies were raised against synthetic peptides of two regions of the surface protein VP1 of foot-and-mouth disease virus. The peptides were conjugated with keyhole limpet hemocyanin via C- or N-terminal amino acid residues by use of different coupling agents. The fine specificity of the resulting antibodies was determined by PEPSCAN methods.

Antigenicity and immunogenicity of synthetic peptides of foot-and-mouth disease virus.

Peptides reactive with two neutralizing monoclonal antibodies raised against intact foot-and-mouth disease virus A10 were identified with the aid of all overlapping (hexa)peptides of the outer structural viral protein VP1 and located on the viral surface. Using this procedure, it was possible to define those amino acids within a peptide which were critical in the binding of antibody to that peptide. One eight amino acid long peptide, containing six such amino acids, was virtually indistinguishable from viral antigen in its ability to bind monoclonal antibody as determined by competition tests.