Department of Crystal and Structural Chemistry

Padualaan 8 (H.R. Kruytgebouw), 3584 CH Utrecht, the Netherlands
phone: +31-30-2533502 (secr.) fax: +31-30-2533940, e-mail: secrks@chem.uu.nl
 

Research group of Eric Huizinga


picture of Eric Huizinga




Eric Huizinga
Assistant Professor
(universitair docent onderzoeker)
email: e.g.huizinga@chem.uu.nl

Research high-lights: Structural basis of von Willebrand factor-mediated platelet adhesion

An essential first step in the arrest of bleeding is the adhesion of blood platelets to a damaged vessel wall. In this process the large multimeric glycoprotein von Willebrand Factor (VWF) functions as a bridge between blood platelets and collagen fibers exposed at sites of vascular damage. A fascinating aspect of VWF is that it has no significant interaction with platelets in the absence of vascular damage, but binds platelets rapidly once VWF becomes immobilized at sites of vascular damage or is exposed to high shear stress. In a long-standing collaboration with the Thrombosis and Haemostasis Laboratory of the University Medical Center Utrecht we study the structural basis of von Willebrand factor mediated platelet adhesion. We solved the crystal structure of the collagen-binding A3 domain of von Willebrand factor [1]and mapped the position of its collagen-binding site by a combination of co-crystallisation with an inhibiting antibody and site-directed mutagenesis [3][5].

VWF-A3 domainRibbon drawing of the crystal structure of the VWF-A3 domain. The color of residues shown in ball-and-stick reflects the effect of their mutation to alanine on collagen binding (red/magenta abolish collagen binding; green decreased binding; grey no effect). The shape and location of the collagen binding site of VWF-A3 is strikingly different from collagen binding sites found in homologous integrin I-type domains. VWF-A3 has a rather flat binding site in one of its side faces, while integrin I-domains have a groove shape binding site located at their top-face.


We also determined the crystal structure of the VWF-A1 domain bound to an N-terminal fragment of its platelet-receptor named glycoprotein [4]. These structures provided important insights in the structural basis of bleeding disorders and suggested how shear stress acting on immobilized VWF may activate GpIb-alpha binding (see figure legend).

VWF-GpIb complexOn the left: Ribbon drawing of the A1 domain of VWF (blue and red) bound to the VWF-binding domain of GpIb-alpha (green). Shown in red ball-and-stick are two mutated residues, R543Q in VWF-A1 and M239V in GpIb-alpha that enhance complex formation and cause von Willebrands disease. We introduced these mutations to obtain a strong complex for crystallisation. Upon complex formation a surface exposed loop, called beta-switch, that is disordered in the structure of free GpIb-alpha (shown on the right) changes its conformation to a beta-hairpin and aligns with the central beta-sheet of VWF-A1. Mutation 239V is located in this loop region and likely stabilizes the hairpin conformation thereby enhancing the affinity of GpIb-alpha for VWF. The R543Q mutation is located at the  base of VWF-A1 and apparently destabilizes the conformation of its N- and C-terminal peptides that may shield the GpIb-alpha binding site in a low affinity conformation of VWF. Under physiological conditions displacement of the terminal peptides may result from a pulling force created by shear stress acting on VWF immobilized onto collagen thereby providing activation of platelet adhesion.


Current research focusses on the mechanism of activation of the VWF/GpIb-alpha interaction and on the interaction of VWF with blood coagulation factor VIII.
 

Key references

  1. Crystal structure of the A3 domain of human von Willebrand factor: implications for collagen binding. E.G. Huizinga, R.M. van der Plas, J. Kroon, J.J. Sixma & P. Gros. Structure 5,1147-1156 (1997)
  2. The structure of Leach Anti-Platelet Protein, an inhibitor of haemostasis. E.G. Huizinga, A. Schouten, T. Connolly, J. Kroon, J. Sixma & P. Gros. Acta. Cryst., D57, 1071-1078 (2001).
  3. Identification of the collagen-binding site of the von Willebrand Factor A3-domain. R.A.P. Romijn, B.Bouma, W.W. Wuyster, P.Gros , J. Kroon, J.J. Sixma & E.G. Huizinga. J. Biol Chem., 276, 9985-9991 (2001).
  4. Structures of Glycoprotein Ib alpha and its complex with von Willebrand Factor A1 domain. E.G. Huizinga, S. Tsuji, R.A.P. Romijn, .E. Schiphorst, Ph.G. de Groot, J.J. Sixma & P. Gros. Science, 297, 1176-1179 (2002).
  5. Mapping the collagen-binding site in the von Willebrand Factor A3-domain. R.A. Romijn, E. Westein, B. Bouma, M.E. Schiphorst, J.J. Sixma, P.J. Lenting &  E.G. Huizinga. J. Biol. Chem., 278, 15035-15039 (2003).

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