Interaction of Shiga Toxin with the A-domains and Multimers of von Willebrand Factor

Background: VWF is a multimeric glycoprotein that causes platelet adherence and aggregation and is cleaved by ADAMTS-13. Results: Shiga toxin binds to VWF multimers, specifically the A1 and A2 domains, and decreases ADAMTS-13 cleavage rate at Tyr(1605)-Met(1606) of the A2 domain. Conclusion: Shiga toxin binding to VWF impairs ADAMTS-13 cleavage. Significance: Delayed VWF cleavage may contribute to renal thrombotic microangiopathy in Shiga toxin-induced hemolytic uremic syndrome. Shiga toxin (Stx) produced by enterohemorrhagic Escherichia coli causes diarrhea-associated hemolytic-uremic syndrome (DHUS), a severe renal thrombotic microangiopathy. We investigated the interaction between Stx and von Willebrand Factor (VWF), a multimeric plasma glycoprotein that mediates platelet adhesion, activation, and aggregation. Stx bound to ultra-large VWF (ULVWF) secreted from and anchored to stimulated human umbilical vein endothelial cells, as well as to immobilized VWF-rich human umbilical vein endothelial cell supernatant. This Stx binding was localized to the A1 and A2 domain of VWF monomeric subunits and reduced the rate of ADAMTS-13-mediated cleavage of the Tyr(1605)-Met(1606) peptide bond in the A2 domain. Stx-VWF interaction and the associated delay in ADAMTS-13-mediated cleavage of VWF may contribute to the pathophysiology of DHUS.