Comparison of the Nd6 complex structure with other A1 structures suggests a model of VWF autoinhibition and activation. (A) Overlaid Nd6 and VHH81 complex structures, with resolved AIM residues zoomed in and highlighted in the box on the right. Nd6 is shown in green, VHH81 in pink, and both AIM-A1 in gray. Resolved NAIM and CAIM residues from the Nd6 structure are shown in sky blue and orange, respectively. Resolved NAIM and CAIM residues from the VHH81 structure are shown in light purple and yellow, respectively. (B) Ribbon diagram of the A1/LBD complex structure (PDB: 1sq0), with the resolved AIM residues highlighted in purple and magenta. (C) Overlaid Nd6 and LBD complex structures, showing only AIM-A1 from the Nd6 complex structure and LBD from the LBD complex structure. The highlight box on the right shows the overlap of resolved AIM residues with the N-terminus of the LBD. (D) Illustration of the AIM model of VWF autoinhibition and activation. A structured AIM would have steric hindrance with the LBD, thus shielding A1 from binding to LBD. Conformationally insensitive nanobodies, such as 6D12 and 6C11, can bind to the NAIM residues distal from the A1 domain and disrupt the AIM, which exposes A1 for binding to the LBD. Conversely, conformationally sensitive nanobodies such as Nd6 and VHH81 can bind and stabilize the AIM, thus inhibiting A1 binding to the LBD.