Joshua Muia

Allosteric activation of ADAMTS13 by von Willebrand factor

Significance The blood protein von Willebrand factor (VWF) is required for platelets to stop bleeding at sites of injury, and the metalloprotease ADAMTS13 limits platelet adhesion by cleaving VWF only when flowing blood stretches it, especially within a growing thrombus. This feedback inhibition is essential because ADAMTS13 deficiency causes fatal microvascular thrombosis. How ADAMTS13 recognizes VWF so specifically is not understood. We now find that ADAMTS13 is folded roughly in half so that its distal domains inhibit the metalloprotease domain. VWF relieves this autoinhibition and promotes its own destruction by allosterically activating ADAMTS13. Thus, VWF is both a substrate and a cofactor in this critical regulatory process. The metalloprotease ADAMTS13 cleaves von Willebrand factor (VWF) within endovascular platelet aggregates, and ADAMTS13 deficiency causes fatal microvascular thrombosis. The proximal metalloprotease (M), disintegrin-like (D), thrombospondin-1 (T), Cys-rich (C), and spacer (S) domains of ADAMTS13 recognize a cryptic site in VWF that is exposed by tensile force. Another seven T and two complement C1r/C1s, sea urchin epidermal growth factor, and bone morphogenetic protein (CUB) domains of uncertain function are C-terminal to the MDTCS domains. We find that the distal T8-CUB2 domains markedly inhibit substrate cleavage, and binding of VWF or monoclonal antibodies to distal ADAMTS13 domains relieves this autoinhibition. Small angle X-ray scattering data indicate that distal T-CUB domains interact with proximal MDTCS domains. Thus, ADAMTS13 is regulated by substrate-induced allosteric activation, which may optimize VWF cleavage under fluid shear stress in vivo. Distal domains of other ADAMTS proteases may have similar allosteric properties.

Linker regions and flexibility around the metalloprotease domain account for conformational activation of ADAMTS-13

Recently, conformational activation of ADAMTS‐13 was identified. This mechanism showed the evolution from a condensed conformation, in which the proximal MDTCS and distal T2‐CUB2 domains are in close contact with each other, to an activated, open structure due to binding with von Willebrand factor (VWF).

An optimized fluorogenic ADAMTS13 assay with increased sensitivity for the investigation of patients with thrombotic thrombocytopenic purpura.

Most ADAMTS13 assays use non‐physiological conditions (low ionic strength, low pH, barium chloride), are subject to interference from plasma proteins, hemoglobin and bilirubin, and have limited sensitivity, especially for inhibitors.

Early career professionals: A challenging road

The term “early career professional” (ECP) indicates a generation of professionals that demonstrates the potential to succeed established professionals and leaders. The field of thrombosis and hemostasis has a large ECP community. They often face typical challenges in their endeavor to establish an independent academic career. A healthy work‐life balance and mentoring are key for ECPs to create the ideal circumstances to advance their careers. However, multitasking training, research and clinical duties is a burden, and burnout is a looming issue. The advent of the smartphone presents an additional challenge by blurring the border between work and non‐work time. This Forum describes some of the typical challenges faced by ECPs, highlights existing literature and suggests practical solutions relevant to ECPs in the field of thrombosis and hemostasis, and the possible role of the ISTH Early Career Committee.

Reflections on scientific collaboration between basic researchers and clinicians

Early career researchers face uncertainties with respect to their job prospects due to dwindling job markets, decreased availability of funding and undefined career paths. As basic researchers and clinicians tend to have different approaches to scientific problems, there are many advantages from successful collaborations between them. Here, we discuss how collaborations between basic and clinical scientists should be promoted early in their careers. To achieve this, researchers, both basic and clinical, must be proactive during their training and early stages of their careers. Mentors can further augment collaborative links in many ways. We suggest that universities and institutions might reassess their involvement in promoting collaborations between basic and clinical researchers. We hope that this paper will serve as a reminder of the importance of such collaborations, and provide the opportunity for all members of the scientific community to reflect on and ameliorate their own contributions.