Von Willebrand factor (VWF) is synthesized by endothelial cells and megakaryocytes, and released as a multimeric glycoprotein into the peripheral blood stream. Ultra large VWF multimers are formed in the Golgi apparatus. In circulation, VWF senses a vessel injury and induces platelet adhesion to vascular injury sites (Reininger AJ 2008; Mojzisch A & Brehm MA 2021). VWF also functions as a carrier protein for factor VIII (FVIII), stabilizing FVIII, which otherwise has a very short half-life in the bloodstream (Kaufman RJ et al., 1997). VWF activity is dependent on its extent of multimerization, as larger VWF structures are more thrombogenic and display higher platelet tethering capacity at sites of a vascular injury. Under normal physiological conditions, ultra large VWF multimers are cleaved into smaller units by a disintegrin and metalloproteinase with thrombospondin type 1 repeats 13 (ADAMTS13) in a shear-dependent manner (Shim K et al., 2008; Zhang X et al., 2009). ADAMTS13 downregulates VWF procoagulant activity by cleaving the peptide bond between Tyr1605 and Met1606 within the A2 domain of VWF (Furlan M et al., 1996; Tsai HM 1996; Crawley JTB et al., 2011). ADAMTS13 is primarily expressed by hepatic stellate cells in the liver and is secreted into the bloodstream as an active enzyme (Zhou W et al., 2005) which circulates in its inactive (closed) conformation (South K et al., 2014; Petri A et al., 2019; Geist N et al., 2022). The closed conformation of ADAMTS13 is maintained by the interaction between the C-terminal CUB1-2 domains and the spacer domain of ADAMTS13 (South K et al., 2014; Kim HJ et al., 2021; reviewed in Ercig B et al., 2021). Structural and biochemical studies have revealed that ADAMTS13 becomes proteolytically active upon binding to its substrate, VWF (Crawley JTB et al., 2011; South K et al., 2014; Petri A et al., 2019; Geist N et al., 2022). The cleavage of VWF by ADAMTS13 is thought to occur on the surface of endothelial cells during secretion of VWF or at sites of vascular damage where VWF binds to exposed collagen and forms VWF-platelet strings (Dong JF et al., 2003; Shim K et al., 2008; Turner N et al., 2008). Cleavage of VWF multimer has also been detected in circulating blood (Majerus EM et al., 2005). Deficiency or dysfunction of ADAMTS13 has been linked to various bleeding disorders such as thrombotic thrombocytopenic purpura (TTP) (Zheng XL 2015; Sukumar S et al. 2021).
ADAMTS13 binding to VWF is controlled by the conformational changes in the mechanosensitive VWF multimer, which undergoes shear stress-induced transition from a folded, inactive conformation to an unfolded, elongated VWF multimers. In the inactive state, VWF is stabilized by autoinhibitory interdomain interactions that mask binding sites for platelets and ADAMTS13 within the A1 and A2 domain of VWF, respectively (Aponte-Santamaría C et al., 2015; Arce NA et al., 2021; Bonazza K et al., 2022; Zhao YC et al., 2022). In addition, the stability of the VWF A2 domain is maintained by the Ca2+ ion-binding site (CBS) and the vicinal disulfide bond formed by Cys1669-Cys1670 within the A2 domain (Xu AJ & Springer TA 2012; Lynch CJ et al., 2014). These structural features prevent ADAMTST13-mediated cleavage of VWF (Xu AJ & Springer TA 2012; Lynch CJ et al., 2014; Aponte-Santamaría C et al., 2015; Arce NA et al., 2021; Bonazza K et al., 2022; Zhao YC et al., 2022). Shear-induced destabilization of the A2 domain of VWF results in exposing Tyr1605-Met1606 to ADAMTS13 (Zhang X et al., 2009; Baldauf C et al., 2009; Crawley JTB et al., 2011; Petri A et al., 2019). The ADAMTS13:VWF interaction involves multiple contact sites (Gao W et al., 2008; de Groot R et al., 2015; South K et al., 2017; Kretz CA et al., 2018; Petri A et al., 2019; Geist N et al., 2022; reviewed by Crawley JTB et al., 2011; DeYoung V et al., 2022). Surface plasmon resonance and equilibrium binding assays showed binding between CUB1-2 domains of ADAMTS13 and the D4-CK domain of VWR suggesting a release of the spacer domain (South K et al., 2017). Kinetic analyses of substrate proteolysis revealed that the unfolded A2 domain of VWF is recognized by exosites within the cysteine-rich and spacer domains of ADAMTS13, which conjugate VWF and ADAMTS13 in close proximity to each other (Petri A et al., 2019). Then, interaction of the disintegrin-like domain of ADAMTS13 with VWF allosterically activates the adjacent metalloprotease domain of ADAMTS13 (Petri A et al., 2019). Structural insights further confirm the allosteric activation of ADAMTS13 induced by the multi-step VWF binding (Petri A et al., 2019; Geist N et al., 2022).
This Reactome event shows ADAMTS13-mediated cleavage of VWF between Tyr1605-Met1606.
