Autoinhibitory module underlies species difference in shear activation of von Willebrand factor

Abstract

Background Von Willebrand factor (VWF) is a multimeric plasma protein that bridges the gap between vessel injury and platelet capture at high shear rates. Under high shear or tension, VWF can become activated upon the unfolding of its autoinhibitory module (AIM). AIM unfolding exposes the A1 domain, allowing for binding to platelet glycoprotein (GP)Ibα to initiate primary hemostasis. The characteristics of the AIM and its inhibitory properties within mouse VWF are unknown. Objectives To determine and characterize the autoinhibitory properties of mouse VWF. Methods Recombinant mouse VWF A1 fragments containing or lacking the flanking regions around the A1 domain were generated. We tested the ability of these fragments to bind to human or mouse GPIbα and platelets. We compared the unfolding of mouse AIM‐A1 to human AIM‐A1 by single‐molecule force spectroscopy. Results Recombinant mouse AIM‐A1 binds with higher affinity to GPIbα than its human counterpart. Recombinant mouse proteins lacking part of the AIM show increased binding to GPIbα. Activated A1 fragments lacking the AIM can effectively agglutinate platelets across the species barrier. Using single‐molecule force spectroscopy, we determined that the mouse AIM unfolds under forces similar to the human AIM. Additionally, the human AIM paired with mouse A1 largely recapitulates the behavior of human AIM‐A1. Conclusions Our results suggest that the regulation of VWF‐GPIbα binding has been specifically tuned to work optimally in different rheological architectures. Differences in the AIM sequence may contribute to the difference in VWF shear response between human and mice.