ADAMTS13 cleaves multimeric von Willebrand factor (VWF) to regulate VWF-mediated thrombus formation To search ADAMTS13 peptide sequences binding to VWF. a.-phage library expressing various peptides of ADAMTS13 on the surface was screened Using VWF either immobilized or in solution under static condition By the first screening, peprides sharing the c-terminus of spacer domain from Arg(670) to Gln(684) (epitope-A) were selected To explore additional sites, peptide sequences from the first screening were synthesized and added to the second screening Consequently. Pro(618) to Glu(641) (epitope-B) in the middle of spacer domain Was obtained from immobilized VWF condition Synthetic epitope-B peptide inhibited the cleavage of VWF by ADAMTS13, while the synthetic epitope-A peptide did not as efficiently as epitope-B. Elimination Of four amino acids from either sides of epitope-B terminus markedly reduced the inhibitory effect These two sites in the spacer domain may play significant roles in binding to VWF. (C) 2009 Elsevier Inc All rights reserved