The molecular basis of VWF mechano-sensoring: Structure and interactions of VWF domains as the basis for regulation and aggregation

This project aims at dissecting the molecular mechanisms balancing VWF adhesion, activation, and degradation under shear forces by molecular simulations. We focus on the interactions of the VWF A domains and their force-sensitive auto-inhibitory mechanisms to control platelet binding via the A1 domain and proteolysis of the A2 domain by ADAMTS13. How can force be sensed by various interaction sites of the A domains in VWF, with each other and with other proteins?

Also, we will decipher the role of disulfide bonds within VWF, and their response to force in terms of chemical reactions they undergo, namely redox reactions. In fact, all domains of the VWF, importantly also the less understood C and D domains, comprise disulfide bonds, and are thereby heavily cross-linked. This is an interesting functional feature that remains to be explored. We aim at an in-depth analysis of disulfide-bonded cross-links by our computer simulations.

We will use force-probe Molecular Dynamics simulations, in which pulling forces will be applied to various fragments of VWF to mimic the conditions under shear stress.

An additional goal is a molecular picture of the influence of factors of the microenvironment of the VWF other than force, namely pH and ionic strength on VWF function. Our results will be interpreted in the light of inherited VWF related diseases and cross-checked by parallel in vitro and in silico analyses of disease and other mutants (with TP A1), by VWF flow assays as performed in sub-projects TP A2, TP B1, and TP C3, and by VWF stretching experiments (with TP C2).


Figure legend:

The picture shows the dimeric structure of the cysteine rich knot at the very C-terminus of VWF. By using Molecular Dynamics simulations, we recently found evidence that disease mutations in this region abolish disulfide bonds and/or lead to altered dynamics hampering the recognition by protein disulfide isomerase with severe consequences for VWF maturation. For more details, see our joint publication with Maria Brehm and coworkers [1] 

[1] Brehm MA, Huck V, Aponte-Santamaria C, et al. von Willebrand disease type 2A phenotypes IIC, IID and IIE: A day in the life of shear-stressed mutant von Willebrand factor. Thrombosis and haemostasis 2014; 112(1): 96-108.