Mitoquinone Inactivates Mitochondrial Chaperone TRAP1 by Blocking the Client Binding Site

Abstract

Heat shock protein 90 (Hsp90) family proteins are molecular chaperones that modulate the functions of various substrate proteins (clients) implicated in pro-tumorigenic pathways. In this study, the mitochondria-targeted antioxidant mitoquinone (MitoQ) was identified as a potent inhibitor of mitochondrial Hsp90, known as a tumor necrosis factor receptor-associated protein 1 (TRAP1). Structural analyses revealed an asymmetric bipartite interaction between MitoQ and the previously unrecognized drug binding sites located in the middle domain of TRAP1, believed to be a client binding region. MitoQ effectively competed with TRAP1 clients, and MitoQ treatment facilitated the identification of 103 TRAP1-interacting mitochondrial proteins in cancer cells. MitoQ and its redox-crippled SB-U014/SB-U015 exhibited more potent anticancer activity in vitro and in vivo than previously reported mitochondria-targeted TRAP1 inhibitors. The findings indicate that targeting the client binding site of Hsp90 family proteins offers a novel strategy for the development of potent anticancer drugs.

Structure, Function, and Inhibitors of the Mitochondrial Chaperone TRAP1

“…During the ATPase cycle, it interacts with client proteins; the sequential hydrolysis of two ATPs can be coupled with the remodeling of client conformation and the release of the folded or activated client . Considering the increased ATP hydrolysis in the presence of a client protein or a client-mimic ligand, , many consecutive hydrolysis cycles of two ATPs may occur without client release until client proteins are sufficiently folded to reduce TRAP1–client interactions or successfully inserted into protein assemblies as subunits of multiprotein complexes.…”

“…However, SMTIN-P01 induces the degradation of TRAP1 client proteins in cancer cells likely through the inhibition of foldase activity and consequent proteolytic degradation. Meanwhile, client-mimic inhibitors block the TRAP1 interaction with SIRT3, thus holdase, and do not increase the enzyme activity of SIRT3 . Therefore, small-molecule inhibitors targeting ATP and client binding sites can be exploited to understand the chaperone mechanism of TRAP1.…”

“…The cocrystal structure of zebrafish TRAP1 (zTRAP1)–AMPPNP complexed with MitoQ reveals the molecular interaction of MitoQ with the previously unrecognized druggable site in the MD of TRAP1 (PDB: 7EXP). MitoQ simultaneously interacted with both protomers forming the client binding channel in the complex structure; the ubiquinone moiety interacted with the buckled protomer, and the TPP moiety with the straight protomer . Because of the bipartite interaction established by a single molecule of MitoQ, the proper distancing of C 10 between the ubiquinone and the TPP is essential for the interaction; thereby, the short linker MitoQ did not interact with TRAP1 .…”

TRAP1 Chaperones the Metabolic Switch in Cancer

“…Efforts towards the development of ATP-competitive inhibitors for cytosolic Hsp90 have provided lead compounds for optimization to address the dual challenges of mitochondrial localization and TRAP1 specificity. Conjugation to a chemical scaffold such as the mitochondrial-targeting moiety triphenylphosphonium (TPP) is necessary to provide mitochondrial penetrance [ 116 , 117 ]. Specificity for TRAP1 over Hsp90 may also be a necessary consideration, as well-established Hsp90 ATP-competitive inhibitors cannot differentiate between the ATP-binding pockets, potentially leading to off-target toxicity [ 33 ].…”

“…This long linker approach was adapted for other TRAP1 inhibitors as well, including Mitoquinone. TPP-Mitoquinone has shown utility and specificity by targeting the client-binding middle domain of TRAP1 [ 117 ]. Mitoquinone has been demonstrated to have protective properties in various animal models of neurological maladies, such as traumatic brain injury [ 131 ], Huntington’s disease [ 132 ], amyotrophic lateral sclerosis (ALS) [ 133 ], and Alzheimer’s disease [ 134 ].…”