Our lab is focused on factors that regulate hemostasis by affecting the interactions of von Willebrand Factor (VWF) and ADAMTS13. VWF links platelets to exposed collagen at sites of vascular injury. ADAMTS13, a plasma metalloproteinase, cleaves VWF to generate smaller, less thrombogenic fragments. Too much cleavage of VWF leads to a type of von Willebrand disease and too little cleavage leads to thrombotic thrombocytopenic purpura. We have identified a short fragment of ADAMTS13 (ST2) that can enhance the cleavage of VWF by the full-length enzyme. This fragment, ST2, interacts with VWF and changes its conformation (see figure below). Studies are underway to delineate the interaction of ST2 and VWF and to assess changes in VWF conformation. We are also studying the role of endothelial cells in the cleavage of VWF. VWF is released from endothelial cells and has been shown to interact with the endothelial cell surface. We have determined that ADAMTS13 also interacts with the endothelial cell surface and have shown that this interaction enhances the cleavage of VWF. Current work is focused on characterizing the interaction of ADAMTS13 and the endothelial cells. Our other area of focus is the biosynthesis of ADAMTS13. We have shown that O-fucosylation of ADAMTS13 by a newly characterized enzyme, POFUT2, is essential for normal secretion of ADAMTS13. Studies now focus on the interaction of POFUT2 and ADAMTS13 and other proteins within the endoplasmic reticulum. The work of the lab will give key new insights on the regulation of VWF by ADAMTS13 and increase understanding of the control of hemostasis.
ST2, a small non-catalytic fragment of ADAMTS13, enhances cleavage of VWF by full-length ADAMTS13
Increasing amounts of ST2 were included in VWF cleavage assays with ADAMTS13. Cleaved VWF was detected by SDS-PAGE and immunoblotting. Cleavage results in the generation of C- and N-terminal fragments of VWF. Addition of ST2 enhanced the cleavage of VWF by about ten-fold.
