ADAMTS-13, also known as von Willebrands factor-cleaving protease (vWF-cp), was first identified by its ability to cleave the ultra-large aggregates of vWF into smaller forms in the serum. A thrombocytopenic disorder called thrombic thrombocytopenic purpura (TTR) was shown to be due to a deficiency in the cleavage of von Willebrands factor, and ADAMTS-13 was identified as the enzyme responsible. ADAMTS-13 cleaves the Tyr1605-Met1606 bond in the A2 domain of vWF, a process stimulated by shear stress in the circulation and by binding to either platelet glycoprotein IB_ or to heparin. The cleaved vWF leads to decreased platelet adhesion. An idiopathic form of TTR is found in patients with auto-antibodies to ADAMTS-13. When the von Willebrand-cleaving protease was cloned it was found to be a member of the ADAMTS family, (A Disintigrin And Metalloproteinase with ThromboSpondin motifs) a larger family of secreted metalloproteinases. ADAMTS-13 contains the canonical HExxHxxxxxH zinc metalloproteinase motif found in the active ADAMs proteinases. In addition to the metalloprotease domain, ADAMTS-13 has a propeptide domain, a Prohormone Convertase (PC, furin) cleavage site, a disintegrin domain, a cysteine-rich domain, two CUB domains and eight thrombospondin-1 like domains. Slice variants that lack part of the disintegrin domain, or with longer TS domains have been reported, leading to speculation about their different activities. ADAMTS-13 does not have a transmembrane domain, unlike many of the ADAMs proteases, and is a secreted protein. ADAMTS-13 message is highest in the liver, and concentrations of 1 ug/ml in normal human plasma have been reported. The full length ADAMTS-1 sequence codes for a 1,427 amino acid protein, with a predicted mass of 153.6 kDa, but glycosylation and the abundance of cysteine residues gives ADAMTS-13 an apparent molecular weight of about 190 kDa on reduced SDS PAGE gels. The variants reported include 1,371, 1,340 and 344 amino acids, with predicted mass of 130.3, 144.5 and 36.7 kDa respectively. Many bands of varying sizes can be seen on Western blots, between 110-190 kDa, perhaps indicating differentially processed ADAMTS-13. A recommended starting concentration for Western blots is 1:1,000 when using colorimetric substrates such as BCIP/NBT, and 1:5,000 for chemiluminescent substrates. Higher concentrations of antibody may be needed for samples from more distantly related species. EDTA/EGTA treatment of tissues or lysates is required to see latent zymogen.

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