Differential targeting of von Willebrand factor depending on oxidizing conditions

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Project Summary / Abstract The blood protein von Willebrand factor (VWF) is a large multimeric protein that, when activated, binds to blood platelets tethering them to the site of vascular injury initiating blood coagulation. This process is critical for normal haemostasis, but especially under inflammatory conditions it is thought to be a major player in patho- logical thrombus formation. For this reason, VWF has been the target for the development of anti-thrombotic therapeutics. However, a particular challenge is how to prevent pathological thrombus formation while still allow- ing normal physiological blood coagulation. In fact, currently available anti-thrombotic therapeutics are known to cause intracranial bleeding as side effect. The work presented here proposes that by identifying the confor- mational changes that VWF undergoes in inflammation it will be possible to design molecules that target VWF selectively only in an inflammatory pro-thrombotic environment. Experiments performed in vitro have indicated that oxidizing agents released during inflammation increase the platelet-binding activity of VWF, and this has been linked to the oxidation of methionine residues within VWF. This study aims to characterize what inhibitory mechanisms are removed in VWF through methionine oxidation and identifies sites that can be targeted optimally under oxidizing conditions. We hypothesize that oxidation activates the A1 domain (the domain in VWF that contains the binding site to platelets) by removing the masking function of its neighboring domains. Through a combination of a dynamic flow assay, equilibrium unfolding experiments and a binding assay, we will identify which auto-inhibitory mechanisms of VWF are turned off by oxidation and which methionine residues are key for activation under oxidizing conditions. This knowledge will then be used in computational docking studies to create a model of the complex between the A1 domain and its neighboring domains and study the structural effects of methionine oxidation at atomic level of detail. An assay using samples from patients with inflammatory conditions will be used to test the link between inflammatory conditions and higher activity of VWF in vivo. The structural insights gained here will be invaluable to structure-based drug design in order to develop therapeutics that target VWF only when it is in its oxidized state in order to prevent thrombosis while allowing haemostasis.