1These authors contributed equally to this work.
Shear-induced unfolding activates von Willebrand factor A2 domain for proteolysis
Article first published online: 8 OCT 2009
© 2009 International Society on Thrombosis and Haemostasis
Journal of Thrombosis and Haemostasis
Volume 7, Issue 12, pages 2096–2105, December 2009
How to Cite
BALDAUF, C., SCHNEPPENHEIM, R., STACKLIES, W., OBSER, T., PIECONKA, A., SCHNEPPENHEIM, S., BUDDE, U., ZHOU, J. and GRÄTER, F. (2009), Shear-induced unfolding activates von Willebrand factor A2 domain for proteolysis. Journal of Thrombosis and Haemostasis, 7: 2096–2105. doi: 10.1111/j.1538-7836.2009.03640.x
- Issue published online: 23 NOV 2009
- Article first published online: 8 OCT 2009
- Received 25 May 2009, accepted 16 September 2009
- force-probe molecular dynamics;
- Rossmann fold;
- shear flow;
- ultra-large von Willebrand factor
Summary. Background: To avoid pathological platelet aggregation by von Willebrand factor (VWF), VWF multimers are regulated in size and reactivity for adhesion by ADAMTS13-mediated proteolysis in a shear flow dependent manner. Objective and methods: We examined whether tensile stress in VWF under shear flow activates the VWF A2 domain for cleavage by ADAMTS13 using molecular dynamics simulations. We generated a full length mutant VWF featuring a homologous disulfide bond in A2 (N1493C and C1670S), in an attempt to lock A2 against unfolding. Results: We indeed observed stepwise unfolding of A2 and exposure of its deeply buried ADAMTS13 cleavage site. Interestingly, disulfide bonds in the adjacent and highly homologous VWF A1 and A3 domains obstruct their mechanical unfolding. We find this mutant A2 (N1493C and C1670S) to feature ADAMTS13-resistant behavior in vitro. Conclusions: Our results yield molecular-detail evidence for the force-sensing function of VWF A2, by revealing how tension in VWF due to shear flow selectively exposes the A2 proteolysis site to ADAMTS13 for cleavage while keeping the folded remainder of A2 intact and functional. We find the unconventional ‘knotted’ Rossmann fold of A2 to be the key to this mechanical response, tailored for regulating VWF size and activity. Based on our model we discuss the pathomechanism of some natural mutations in the VWF A2 domain that significantly increase the cleavage by ADAMTS13 without shearing or chemical denaturation, and provide with the cleavage-activated A2 conformation a structural basis for the design of inhibitors for VWF type 2 diseases.