The VWF binding site for FVIII exists in multiple disulfide-bonded states in the circulation. (A) Ribbon representation of the solution structure of the TIL’ (residues 764-827 in wheat) and E’ (residues 828-863 in light green) domains of VWF⁷ (PDB identifier 2mhq). The cysteine residues comprising the eight disulfide bonds are shown as yellow and cyan spheres and the residue numbers indicated. The cysteines in cyan are those residues where the redox state was measured by differential alkylation and by mass spectrometry. (B) Ribbon representation of the crystal structure of the TIL’ (residues 764-827 in wheat), E’ (residues 828-863 in light green), D3 (residues 864-1037 in light blue), C8-3 (residues 1038-1127 in light orange), TIL3 (residues 1128-1196 in pink) and E3 (residues 1197-1252 in cyan) domains of VWF¹¹ (PDB identifier 6n29). The cysteine residues comprising the 25 disulfide bonds are shown as yellow and cyan spheres and the residue numbers indicated. The cysteines in cyan are those residues where the redox state was measured by differential alkylation and by mass spectrometry. (C) Redox states of five TIL’, 1 E’, two D3, four C8-3 and 1 TIL3 disulfides in 13 healthy human donors (7 male - closed symbols; 6 female - open symbols). The bars and errors are mean ± SD. SD, standard deviation.