Wrapping it up: structural basis of ADAMTS-13 global latency.

BACKGROUND

ADAMTS-13 is a critical enzyme that cleaves ultralarge von Willebrand factor multimers, preventing the formation of microthrombi in the microvasculature. Dysfunction or deficiency leads to thrombotic thrombocytopenic purpura. ADAMTS-13 exhibits 2 latency mechanisms: local latency within the metalloprotease (MP) domain and global latency affecting its overall conformation. The interaction of the 2 CUB domains with Spacer is established. The contributions of TSP7, TSP8, and the flexible Linker (L3) have been noted but never mechanistically elucidated. Monoclonal antibodies (mAbs) targeting cryptic epitopes within the MP domain only bind conformationally active ADAMTS-13, through Spacer-CUB dissociation, yet the structural basis of this long-range effect remained unknown.

OBJECTIVES

We aim to establish a unified structural model of ADAMTS-13 autoinhibition, explaining the mechanism of global latency and accounting for cryptic epitope exposure and remote activity constraints.

METHODS

We combined extensive enhanced-sampling molecular dynamics simulations using the TIGER2hPE method with experimental data, including mAb-binding studies, conformational assays under pH and EDTA perturbation, and previously reported biochemical and structural observations.

RESULTS

We present a unified autoinhibition model of ADAMTS-13 and atomistic structure in which its distal domains directly occlude substrate-binding exosites, thereby modulating enzymatic activity. At that position, TSP7 and TSP8 bind directly to the MP module, while the L3 region acts as a pseudosubstrate that mimics the natural von Willebrand factor A2 substrate and blocks the MP-, disintegrin-, and Cys-rich-binding sites.

CONCLUSION

This work provides the first unified structural architecture for ADAMTS-13 global latency, reconciles a broad body of experimental observations, and establishes a testable framework for future mechanistic and experimental studies.