Implications of the VWF CK-PDI A-domain complex from protein–protein docking. (A) Minimum distance, d, between the PDI A domain catalytic site and the CK dimer cysteines involved in dimerization (sulfur–sulfur distances are shown). PDI was docked to either the wt or the hypothetical p.Cys2771Arg CK dimer. The complete dimer (green) or a truncated CK dimer (blue), lacking the C termini, was considered in each case (n = 25 for each set). (B) Typical conformation of the catalytic A domain of PDI (magenta) in complex with the wtCK dimer (monomers: green and cyan), recovered from docking. The cysteine side chains of CK and the catalytic site of PDI (CS) are shown in stick representation. CK termini prevent the CS from accessing the CK cysteines. (C) Structure of the typical docking conformation of PDI–wtCK complex (same colors and representations as in B) when the CK C-terminal amino acids were removed to mimic opening of C-termini. The PDI CS approaches the indicated CK cysteines. (D) Proposed mechanism of CK dimerization mediated by PDI.