Crystal structures of the noncatalytic domains of ADAMTS13 reveal multiple discontinuous exosites for von Willebrand factor.

ADAMTS13 specifically cleaves plasma von Willebrand factor (VWF) and thereby controls VWF-mediated platelet thrombus formation. Severe deficiencies in ADAMTS13 can cause life-threatening thrombotic thrombocytopenic purpura. Here, we determined 2 crystal structures of ADAMTS13-DTCS (residues 287-685), an exosite-containing human ADAMTS13 fragment, at 2.6-A and 2.8-A resolution. The structures revealed folding similarities between the disintegrin-like (D) domain and the N-terminal portion of the cysteine-rich domain (designated the C(A) domain). The spacer (S) domain forms a globular functional unit with a 10-stranded beta-sandwich fold that has multiple interaction sites with the C(A) domain. We expressed 25 structure-based mutants of ADAMTS13-MDTCS (residues 75-685) and measured their enzymatic activity. We identified 3 VWF-binding exosites on the linearly aligned discontinuous surfaces of the D, C(A), and S domains traversing the W-shaped molecule. Since the MDTCS domains are conserved among ADAMTS family proteins, the structural framework of the multiple enzyme-substrate interactions identified in the ADAMTS13-VWF system provides the basis for a common substrate recognition mode in this class of proteinases.