CUB-1 peptides blocked ADAMTS13 binding to immobilized ULVW. (A) Beads coated with ADAMTS13 were perfused over immobilized ULVWF in the presence or absence of recombinant CUB-1 polypeptide (CUB-1, 100 nM) or synthetic peptides (CUB-1A-E, 200 μM). ADAMTS13 beads adhered to immobilized ULVWF and the adhesion was blocked by the recombinant CUB-1 polypeptide and CUB-1A-E peptides, but not by the CUB-1As polypeptide (Student t test, n = 4, ^*P < .01 compared with untreated ADAMTS13 beads). (B) Washed platelets were perfused over histamine-activated HUVECs in the presence of either wild-type ADAMTS13 or the truncation mutant TSP-2. The numbers of strings detected after 2 minutes of perfusion were counted. CUB-1 polypeptide partially blocked the cleavage of ULVWF by wild-type ADAMTS13 as demonstrated by the increased numbers of ULVWF strings, but not by the TSP-2 truncation mutant (Student t test, n = 4). (C) Binding of ULVWF to wild-type ADAMTS13 or TSP-2 mutant was measured by ELISA. ULVWF bound wild-type ADAMTS13 and TSP-2 mutant. The binding to wild-type ADAMTS13 can be partially blocked by an anti-ADAMTS13 antibody (10 μg/mL) generated using as an immunogen a synthetic peptide from the CUB-1 domain (Student t test, n = 7). All data are expressed as mean ± SEM.