Mapping of the binding sites of the human anti-ADAMTS13 mAbs to the spacer domain using conformational CLIPS peptide technology. (A) Crystal structure and amino acid spacer domain of ADAMTS13 with residues 560 to 575 (green loop), residues 585 to 615 (blue loop), residues 653 to 675 (yellow loop), and residues 628 to 643 (magenta loop) highlighted. Red amino acid residues are part of the key epitope recognized by autoantibodies published previously by others. (B-G) Mapped binding sites of the anti-ADAMTS13 mAbs are highlighted in red. The binding patterns were categorized into 3 groups, with group 1 and 2 consisting of several mAbs recognizing the same conformational epitope. (B) Group 1 (12/23 mAbs: Fabs 1a, 1d, 1e, 2c, 3h and whole IgG A-1, A-2, A-3, A-5, B-1, B-4, B-8) binding to residues 595 to 605 (within the blue loop, A). (C) Group 2 (7/23 mAbs: Fab 2i, 2j, 3b, 3j, 4a and whole IgG B-3, B-7) binding to residues 595 to 605 (within the blue loop), residues 564 to 574 (within the green loop), and residues 655 to 665 (within the yellow loop). (D-G) Group 3 (4/23 mAbs): each with an unique epitope pattern, for whole (D) IgG B-2 residues 661 to 671 (within the yellow loop); (E) Fab 1h residues 562 to 570 (within the green loop) and 587 to 595 (within blue loop); (F) Fab 2a residues 655 to 665 (within the yellow loop) and residues 568 to 578 (within the green loop); and (G) Fab 2h residues 580 to 600 (blue loop only). Six of the 29 anti-ADAMTS13 mAbs could not be mapped: Fabs 1f, 1g, and 3c and whole IgGs A-6, B-5, and B-6.