# Conformational activation of von Willebrand factor

> **NIH NIH R01** · EMORY UNIVERSITY · 2021 · $618,888

## Abstract

PROJECT SUMMARY
 Large, multimeric plasma protein von Willebrand factor (VWF) critically mediates hemostasis and
thrombosis by sensing and responding to blood shear flow. Under low shear conditions, VWF multimers
in circulation adopt a loosely coiled, condensed shape as a result of weak interactions between VWF
monomers. Above a critical shear rate, VWF multimers extend in the direction of elongational flow and
experience tensile force, which has two opposing effects. Tension induces structural changes around the
VWF A1 domain that promote binding to platelet glycoprotein (GP)Ibα and support platelet adhesion and
activation. Tension also unfolds the VWF A2 domain to expose a Tyr-Met peptide bond that is cleaved by
the metalloprotease ADAMTS13, thereby releasing adherent platelets and reducing the VWF reactivity.
Thus, VWF size and reactivity are in an exquisitely regulated balance. Disruption of this balance is a
common cause of bleeding or thrombosis. Previous studies have established that under low shear
conditions both VWF and ADAMTS13 are autoinhibited. However, the underlying molecular mechanisms
for autoinhibition are not clear, which has severely limited understanding of shear-induced effects on
VWF as well as its interactions with GPIbα and ADAMTS13. Although atomic structures of many
domains of VWF and ADAMTS13 have been determined, full-length VWF and ADAMTS13 are large and
flexible. As a result, critical interdomain interactions in each protein, and VWF-ADAMTS13 interactions,
are not accessible to X-ray crystallography. We have circumvented this limitation through a combination
of hydrogen-deuterium exchange mass spectrometry (HDX-MS), electron microscopy (EM), small angle
X-ray scattering (SAXS), analytical ultracentrifugation (AUC), and molecular modeling. In this project we
will employ these methods to characterize the dynamic interactions in and between VWF, ADAMTS13,
and GPIbα, as proposed in the following 2 Specific Aims. Aim 1 is to elucidate the mechanism of VWF
autoinhibition and activation. We will characterize how the A1 domain is masked by the autoinhibitory
module (AIM) in VWF multimers and various recombinant fragments, and determine the factors that
disrupt or stabilize the AIM-A1 interaction and their impacts on A1 binding to GPIbα. Aim 2 is to
determine how force regulates interactions between VWF and ADAMTS13. We will determine the
structure of autoinhibited ADAMTS13, and characterize the conformational changes in ADAMTS13 upon
allosteric activation by VWF fragments that simulate the unfolded A2 domain. We expect to develop
detailed, molecular models that will explain key functions of this remarkable molecular machine of
VWF/ADAMTS13/GPIbα in unprecedented detail. The results will provide a foundation to manipulate
platelet adhesion, and the feedback inhibition of platelet adhesion, for therapeutic purposes.

## Key facts

- **NIH application ID:** 10183306
- **Project number:** 5R01HL143794-04
- **Recipient organization:** EMORY UNIVERSITY
- **Principal Investigator:** Renhao Li
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $618,888
- **Award type:** 5
- **Project period:** 2018-08-01 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10183306

## Citation

> US National Institutes of Health, RePORTER application 10183306, Conformational activation of von Willebrand factor (5R01HL143794-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10183306. Licensed CC0.

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