VWF domain structure and magnetic tweezers assay. (A) Domain sequence of a full-length VWF monomer.⁴  Domains are scaled to length. The propeptide is cleaved by furin before mature VWF concatemers are secreted into the bloodstream. Binding sites of different interaction partners of VWF are indicated. (B) Mature monomers are dimerized via C-terminal linkage of the CK domains in the ER and subsequently multimerized via N-terminal linkage of 2 D'D3 domains in the trans-Golgi network. (C) Crystal structure of the D'D3 domain in its closed conformation (PDB accession code 6N29).¹⁸  The D'D3 domain comprises 6 submodules: TIL' and E' (D' submodules) project out, whereas C8-3, TIL3, and E3 form a wedge with the larger VWD3 module (D submodules). Cysteines for multimerization are buried in the interface and indicated by yellow spheres. The structure was rendered using VMD.⁴⁷  (D) Schematic of VWF dimer in magnetic tweezers. VWF is covalently attached to a flow cell surface via an ELP linker. Coupling to a paramagnetic bead is achieved via a stable biotin-streptavidin linkage. Reference beads are used to account for drift. Forces are applied through 2 permanent magnets above the flow cell.