Von Willebrand factor (vWF) is a plasme protein that circulates in blood at a concentration of about 50 nM. VWF is a multimeric protein involved in platelet adherence to the injured vessel wall at high shear rates, platelet-platelet interactions and it is a carrier protein for factor VIII. Adhesion of platelets at high shear rates is a multistep process in which vWF functions at first as a molecular bridge between the exposed subendothelial collagen and GpIb-IX-V receptor complexes on platelets, and later on as a molecular glue for platelet-platelet interactions. Absence of vWF results in a severe bleeding tendency while high levels of vWF in the circulation correlates with an increased risk for thrombosis.
The binding site within vWF for collagen is located in the A3-domain. We have recently characterised by site-directed mutagenesis the amino acids present in the A3 domain that are involved in the interaction with collagen. The specific amino acid sequences within the different types of collagen involved in the binding with vWF are unknown.
The binding site within vWF for GPIb is located in the A1-domain. Both vWF and platelets are present in plasma but in the circulation vWF and platelets are unable to interact with each other spontaneously. To induce an interaction, a conversion of the vWF into a Glycoprotein Iba (GpIba)-binding confirmation is required. Activation of vWF can be induced by binding of vWF to collagen (or a plastic surface), or by incubation with modulators such as botrocetin or ristocetin. In von Willebrand Disease (VWD) type 2B, vWF circulates in a GpIba-binding confirmation, due to a gain-of-function mutation in the A1-domain of vWF.
We have recently developed Llama antibodies that specifically recognize vWF in its GPIb binding confirmation. These antibodies are very suitable to measure the presence of 'active' vWF in blood with an ELISA or via immune precipitation or the presence of 'active' vWF in tissue via immunostaining.
The objectives of our current research are:
- To develop assays for the detection of 'active' vWF in the circulation
- To investigate the contribution of circulating 'active' vWF in the development of thrombocytopenia
- To investigate the contribution of circulating 'active' vWF in the risk of thrombotic complications
- To investigate the contribution of circulating 'active' vWF in infectious diseases
- To understand the conformational changes within vWF that result in a GPIb binding confirmation
- To study the distribution of 'active' vWF in different tissues
- To elucidate the amino acid sequence within collagen types I and III responsible for the interaction with vWF
- To understand the interaction between the A3-domain of vWF and collagen at the atomic level
- To develop a potential antithrombotic drug based on interference with the collagen-vWF interaction
On this project are working under supervision of Prof. Dr. Ph.G. de Groot, Dr. P.J. Lenting and Dr. T. Lisman:
- Ir. E. Groot, Ph.D. student
- Drs. J.J.J. Hulstein, Ph.D. student
- Ing. M.J.W. IJsseldijk, technician
In collaboration with:
- Dr. R. Fijnheer, Jeroen Bosch Hospital, Den Bosch, the Netherlands
- Dr. E.G. Huizinga, Department of Crystal and Structural Chemistry, Utrecht University, the Netherlands
- Dr. R.W. Farndale, Department of Biochemistry, Cambridge, United Kingdom
- Dr. R.W. Sauerwein, Department of Medical Microbiology, Radboud Medical Centre, Nijmegen, the Netherlands
- Dr. K. Silence, Ablynx, Ghent, Belgium
Recent publications
Acute activation of the endothelium results in increased levels of active Von Willebrand Factor in HELLP syndrome
Hulstein JJ, van Runnard Heimel PJ, Franx A, Lenting PJ, Bruinse HW, Silence K, de Groot PG, Fijnheer R; J Thromb Haemost 2006 Sep 12, Epub ahead of print
A single high-affinity binding site for von Willebrand Factor in collagen III, identified using synthetic triple-helical peptides
Lisman T, Raynal N, Groeneveld D, Maddox B, Peachey T, Huizinga EG, de Groot PG, Farndale RW; Blood 2006, Prepublished online August 15
FRETS-VWF73: a rapid and predictive tool for thrombotic thrombocytopenic purpura
Groot E, Hulstein JJ, Rison CN, de Groot PG, Fijnheer R; J Thromb Haemost 2006; 4: 698-9
A novel nanobody that detects the gain-of-function phenotype of von Willebrand factor in adamts13 deficiency and Von Willebrand disease type 2B
Hulstein JJ, de Groot PG, Silence K, Veyradier A, Fijnheer R, Lenting PJ; Blood 2005; 106: 3035-42