Insights into 3D Structure of ADAMTS13: A Stepping Stone towards Novel Therapeutic Treatment of Thrombotic Thrombocytopenic Purpura

Abstract

ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type-1 motif, member 13) and von Willebrand factor (VWF) can be considered as scale weights which control platelet adhesion during primary haemostasis. In a very uncommon condition designated thrombotic thrombocytopenic purpura (TTP), functional absence of ADAMTS13 tips the balance toward VWF-mediated platelet adhesion in the microcirculation. TTP is associated with a high mortality and arises from either a congenital or acquired autoimmune deficiency of the plasma enzyme ADAMTS13. In case of acquired ADAMTS13 deficiency, autoantibodies bind to and inhibit the function of ADAMTS13. Currently available treatments of TTP aim to supply ADAMTS13 through plasma exchange or are aimed at B-cell depletion with rituximab. None of the available therapeutics, however, aims at protection of ADAMTS13 from circulating autoantibodies. In this review, our aim is to describe the structure-function relationship of ADAMTS13 employing homology models and previously published crystal structures. Structural bioinformatics investigation of ADAMTS13 reveals many insights and explains how mutations and autoantibodies may lead to the pathophysiology of TTP. The results of these studies provide a roadmap for the further development of rationally designed therapeutics for the treatment of patients with acquired TTP. In addition, we share our opinion on the state of the art of the open-closed conformations of ADAMTS13 which regulate the activity of this highly specific VWF cleaving protease.Ã On behalf of the PROFILE Consortium, http://www.itn-profile.eu/

Child‐onset thrombotic thrombocytopenic purpura caused by p.R498C and p.G259PfsX133 mutations in ADAMTS13

“…In line with this, rhADAMTS13 protein could be visualized via fluorescence microscopy in permeabilized transfected CHO K1 cells with the p.R498C, the p.R498C + p.G259PfsX133, and WT ADAMTS13 while the p.G259PfsX133 mutant could not (Figure B). These data indicate that the p.R498C mutation impairs secretion and that the p.G259PfsX133 mutation, which results in a frameshift mutation at the end of the metalloprotease domain (AA 259 of 80‐286) of ADAMTS13, probably leads to an unstable RNA molecule that impedes translation of the protein.…”

“…This was confirmed by sequence analysis of the ADAMTS13 gene with identification of 2 compound heterozygous mutations: the c.768_774dup frameshift mutation (p.G259PfsX133) and the c.1492C>T ADAMTS13 missense mutation (p.R498C) (Figure A). The 7 nucleotides (CCGCGCC) duplicated in the metalloprotease domain (amino acid, AA 80‐286) induce a frameshift resulting in a premature stop codon in the first thrombospondin type 1 repeat of ADAMTS13 (p. G259PfsX133) (Figure A). The point mutation is located in the cysteine‐rich domain and results in the p.R498C amino acid substitution (Figure A).…”

“…Molecular models of WT and mutant hADAMTS13 were built using homology models of known ADAMTS13 domain structures and the YASARA&WhatfIf package. The p.R498C mutation was introduced with the mutagenesis module of PyMOL 1.8.2.1 (The PyMOL Molecular Graphics System, Version 1.8.2.1 Schrödinger, LLC).…”

“…The 7 nucleotides (CCGCGCC) duplicated in the metalloprotease domain (amino acid, AA 80-286) 28 induce a frameshift resulting in a premature stop codon in the first thrombospondin type 1 repeat of ADAMTS13 (p. G259PfsX133) ( Figure 1A). The point mutation is located in the cysteine-rich domain and results in the p.R498C amino acid substitution ( Figure 1A).…”

A Single Synonymous Variant (c.354G>A [p.P118P]) in ADAMTS13 Confers Enhanced Specific Activity

“…The metalloprotease domain contains a Zn 2+ active site responsible for substrate cleavage in which the Zn ion helps stabilize the charge generated on the carbonyl carbon during VWF A2 cleavage. The disintegrin, cysteine-rich, and spacer domains contain an exosite each that are important for substrate binding and specificity [43]. From multiple sources, it is clear that the ADAMTS13 molecule undergoes many conformational changes in order to bind and cleave its substrate, VWF [44,45].…”