Activation of von Willebrand factor via mechanical unfolding of its discontinuous autoinhibitory module

Nicholas A Arce,Alexander K Brown,Emily R Legan,Emma-Ruoqi Xu,Renhao Li,Wenpeng Cao,Michael C Berndt,Moriah S Wilson,Jonas Emsley,X Frank Zhang

doi:10.1038/s41467-021-22634-x

Abstract

Von Willebrand factor (VWF) activates in response to shear flow to initiate hemostasis, while aberrant activation could lead to thrombosis. Above a critical shear force, the A1 domain of VWF becomes activated and captures platelets via the GPIb-IX complex. Here we show that the shear-responsive element controlling VWF activation resides in the discontinuous autoinhibitory module (AIM) flanking A1. Application of tensile force in a single-molecule setting induces cooperative unfolding of the AIM to expose A1. The AIM-unfolding force is lowered by truncating either N- or C-terminal AIM region, type 2B VWD mutations, or binding of a ristocetin-mimicking monoclonal antibody, all of which could activate A1. Furthermore, the AIM is mechanically stabilized by the nanobody that comprises caplacizumab, the only FDA-approved anti-thrombotic drug to-date that targets VWF. Thus, the AIM is a mechano-regulator of VWF activity. Its conformational dynamics may define the extent of VWF autoinhibition and subsequent activation under force.

Highlights

Von Willebrand factor (VWF) activates in response to shear flow to initiate hemostasis, while aberrant activation could lead to thrombosis
Fitting extension traces of autoinhibitory module (AIM)-A1 to the worm-like chain (WLC) model[34] yields a contour length of 26.6 ± 0.5 nm, suggesting that the underlying unfolding event involves approximately 67 residues, which is remarkably close to the length of both flanking sequences in the AIM-A1 construct (N-terminal 34, C-terminal 32) (Fig. 1D, Supplementary Fig. 3; Table 1)
Deletion of either half of the AIM, the introduction of a type 2B von Willebrand disease (VWD) mutation at the AIM/A1 interface, or addition of a ristocetin-mimicking antibody that binds to CAIM residues results in the significantly decreased mechanical stability of the AIM and drastically increased activity of A1

Summary

Introduction

Von Willebrand factor (VWF) activates in response to shear flow to initiate hemostasis, while aberrant activation could lead to thrombosis. Understanding the mechano-activation mechanism of VWF is key to elucidate the pathophysiology of thrombotic diseases and to develop safe anti-thrombotic therapeutics It has been documented for more than 30 years that under several conditions independent of flow change, VWF can overcome its autoinhibition and bind to GPIbα with high affinity. All reported type 2B mutations are located in the A1 domain or the flanking regions around A114, suggesting that autoinhibitory elements are localized around A1 This is consistent with recent observations that global extension of VWF multimer under flow occurs before a local, tension-dependent activation of the A1 domain for GPIbα binding[5]. The AIM could be targeted effectively by a recently developed antithrombotic agent

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