See also Lenting PJ, Rastegarlari G. ADAMTS-13: double trouble for von Willebrand factor. This issue, pp 2775-7.Summary. Background: vonWillebrandfactor(VWF)released from endothelial cells is rich in ultra-large (UL) multimers that are intrinsically active in binding platelets, whereas plasma-type VWF multimers require shear stress to be activated. This functional difference may be attributed to thiols exposed on the surface of plasma-type VWF multimers, but not on ULVWF multimers. Shear stress induces the exposed thiols to form disulfide bonds between laterally apposed plasma-type VWF multimers, leading to enhanced VWF binding to platelets. Objectives: We tested a hypothesis that ADAMTS-13 has a disulfide bond reducing activity that regulates shear-induced thiol-disulfide exchange of VWF. Methods: Thiol blocking agents and active thiol bead capturing were used to identify and locate this activity, along with truncated ADAMTS-13 mutants. Results: ADAMTS-13 contains a disulfide bond reducing activity that primarily targets disulfide bonds in plasma-type VWF multimers induced by high shear stress or formed with thiol beads, but not disulfide bonds in native multimeric structures. Cysteine thiols targeted by this activity are in the VWF C-domain and are known to participate in shear-induced thiol-disulfide exchange. ADAMTS-13 contains cysteine thiols that remain exposed after being subjected to hydrodynamic forces. Blocking these active thiols eliminates this reducing activity and moderately decreases ADAMTS-13 activity in cleaving ULVWF strings anchored to endothelial cells under flow conditions, but not under static conditions. This activity is located in this C-terminal region of ADAMTS-13. Conclusions: This novel disulfide-bond-reducing activity of ADAMTS-13 may prevent covalent lateral association and increased platelet adherence of plasma-type VWF multimers induced by high fluid shear stress.

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European Journal of Rheumatology (Eur J Rheumatol) is an international, open access peer reviewed journal committed to promoting the highest standards of scientific exchange and education. The journal is published quarterly on January, April, July and October. The aim of the European Journal of Rheumatology is to cover various aspects of rheumatology for its readers, encompassing the spectrum of diseases with arthritis, musculoskeletal conditions, autoinflammatory diseases, connective tissue disorders, osteoporosis, translational research, the latest therapies and treatment programs. European Journal of Rheumatology publishes original articles, invited reviews, case based reviews, letters to the editor and images in rheumatology. The publication language of the journal is English. Accepted manuscripts are copy-edited for grammar, punctuation, and format. Once the publication process of a manuscript is completed, it is published online on the journal's webpage as an aheadof-print publication before it is included in its scheduled issue. A PDF proof of the accepted manuscript is sent to the corresponding author and their publication approval is requested within 2 days of their receipt of the proof.

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