Conventional Molecular Dynamics and Metadynamics Simulation Studies of the Binding and Unbinding Mechanism of TTR Stabilizers AG10 and Tafamidis.

Amyloid transthyretin (ATTR) amyloidosis is a widespread and fatal systemic amyloidosis characterized by the misfolding and amyloid aggregation of transthyretin (TTR). Studies suggest that dissociation of the TTR tetramer is the key step for its misfolding. Because of the importance of tetramer dissociation on ATTR amyloidosis, many TTR stabilizers have been discovered to stabilize the tetramer structure. This paper describes the application conventional molecular dynamics and metadynamics simulations to investigate the binding and unbinding mechanisms of two TTR stabilizers, including AG10 and tafamidis. AG10 has been granted an orphan drug designation by the U.S. Food and Drug Administration (FDA), and tafamidis was the first FDA-approved treatment for ATTR cardiomyopathy. The conventional molecular dynamics simulations reveal that both AG10 and tafamidis can stabilize the TTR tetramer through different mechanisms. AG10 stabilizes TTR tetramer by forming H-bonds with S117 to mimic the protective effect of T119M. Tafamidis stabilizes the tetramer by forming H-bond with S52 in the flexible CD loop to increase its structural stability. Despite the strong binding affinity of tafamidis, the free-energy surface constructed from metadynamics simulation suggests that tafamidis unbinds more readily than AG10 with lower free-energy barriers between the binding state and other intermediates. Finally, by performing pharmacophore analysis, we found two common important moieties of the studied compounds for their binding on the pockets, which can provide valuable guidance for future lead compounds' optimization in designing drugs for ATTR amyloidosis.