Solution structure of human blood protein Von Willebrand factor

Abstract

The binding of multimeric blood plasma protein von Willebrand factor (vWF) to platelet receptor GpIb under high shear stress is an important step regulating atherothrombosis. We coupled light scattering with small-angle neutron scattering (SANS) to study the solution conformation of vWF. vWF resembled a prolate ellipsoid with a minor axis of length ~50nm and a major axis of ~240nm. Analysis using the unified equation and high-resolution shape fitting revealed repeating structures within vWF at different length scales, which were indicative of the multimeric protein (120nm), monomer unit (20.1nm) and individual domains (3.1nm). Treatment of vWF with guanidine-HCl, which increases the susceptibility of vWF for proteolysis by ADAMTS-13, caused local structural changes at length scales below ~8nm without altering protein radius of gyration. The results suggested that vWF adopts a compact conformation in solution with non-covalent interactions between individual domains. This prediction was verified in western blot runs where vWF was randomly crosslinked with homobifunctional linker BS3 prior to dissociation of disulfide linkages between vWF monomers using dithiothreitol (DTT). Here, electrophoresis of BS3 and DTT treated samples resulted in a pattern of dimer and trimer units that suggest intramolecular interaction between protein sub-domains. Overall, our studies reveal the key structural features of vWF in solution and suggest mechanisms by which this protein may undergo conformation change and self-association under fluid shear. Supported by grants NIH HL63014 and HL76211