Concurrent binding of CUB1 and CUB2 had an additive effect on their affinity for the spacer domain of ADAMTS13. Binding between WT MDTCS (A–C) or GoF MDTCS (D–F) to the immobilized C-terminal domain fragments CUB1, CUB2, and CUB1-2 was determined by SPR. Results are representative of three independent experiments. G, global analysis was used to determine KD, and Bmax values were used for the binding between WT MDTCS and the CUB domain fragments (mean ± S.D., n = 3).