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Force-sensitive autoinhibition of the von Willebrand factor is mediated by
interdomain interactions
#MMPMID25954888
Aponte-Santamarķa C
; Huck V
; Posch S
; Bronowska AK
; Grässle S
; Brehm MA
; Obser T
; Schneppenheim R
; Hinterdorfer P
; Schneider SW
; Baldauf C
; Gräter F
Biophys J
2015[May]; 108
(9
): 2312-21
PMID25954888
show ga
Von Willebrand factor (VWF) plays a central role in hemostasis. Triggered by
shear-stress, it adheres to platelets at sites of vascular injury. Inactivation
of VWF has been associated to the shielding of its adhesion sites and proteolytic
cleavage. However, the molecular nature of this shielding and its coupling to
cleavage under shear-forces in flowing blood remain unknown. In this study, we
describe, to our knowledge, a new force-sensory mechanism for VWF-platelet
binding, which addresses these questions, based on a combination of molecular
dynamics (MD) simulations, atomic force microscopy (AFM), and microfluidic
experiments. Our MD simulations demonstrate that the VWF A2 domain targets a
specific region at the VWF A1 domain, corresponding to the binding site of the
platelet glycoprotein Ib? (GPIb?) receptor, thereby causing its blockage. This
implies autoinhibition of the VWF for the binding of platelets mediated by the
A1-A2 protein-protein interaction. During force-probe MD simulations, a
stretching force dissociated the A1A2 complex, thereby unblocking the GPIb?
binding site. Dissociation was found to be coupled to the unfolding of the A2
domain, with dissociation predominantly occurring before exposure of the cleavage
site in A2, an observation that is supported by our AFM experiments. This
suggests that the A2 domain prevents platelet binding in a force-dependent
manner, ensuring that VWF initiates hemostasis before inactivation by proteolytic
cleavage. Microfluidic experiments with an A2-deletion VWF mutant resulted in
increased platelet binding, corroborating the key autoinhibitory role of the A2
domain within VWF multimers. Overall, autoinhibition of VWF mediated by
force-dependent interdomain interactions offers the molecular basis for the
shear-sensitive growth of VWF-platelet aggregates, and might be similarly
involved in shear-induced VWF self-aggregation and other force-sensing functions
in hemostasis.
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