Ngoc Dung Pham

Deubiquitinase-targeting chimera (DUBTAC) is a promising technology for inducing targeted protein stabilization (TPS). Despite its therapeutic potential, very few proteins have been stabilized by DUBTACs to date. The limited applicability of this technology is likely due to the modest DUBTAC-induced protein stabilization effect, and the scarcity of effective deubiquitinase ligands that can be harnessed for DUBTAC development. Here, we report the discovery of MS7829 and MS8588, the first-in-class DUBTACs of cGAS, a key component of the cGAS-STING pathway. While these DUBTACs are based on a cGAS inhibitor, they effectively stabilized cGAS and activated the cGAS/STING/IRF3 signaling. To develop these cGAS DUBTACs, we optimized EN523, an OTUB1 covalent ligand, into an improved ligand, MS5105. We validated MS5105 by generating a MS5105-based CFTR DUBTAC, which was approximately 10-fold more effective in stabilizing the ΔF508-CFTR mutant protein than the previously reported EN523-based CFTR DUBTAC. Overall, this work advances the DUBTAC technology for TPS.

Mitochondria maintain a distinct biochemical environment that cooperates with pro-apoptotic BAX and BH3‑only proteins (e.g., BIM) to promote mitochondrial outer membrane permeabilization (MOMP), the key event to initiate physiological and pharmacological forms of apoptosis. The sphingosine-1-phosphate metabolite 2-trans-hexadecenal (2t‑hexadecenal) is a bioactive lipid that supports BAX-dependent MOMP. Using integrated structural and computational approaches, we determine that 2t‑hexadecenal binds within a distinct, dynamic region-a hydrophobic cavity formed by core-facing residues of α5, α6, and gated by α8-we now term the "BAX actuating funnel" (BAF). Complementary biochemical and biophysical techniques reveal that 2t-hexadecenal non-covalently interacts with the BAF and cooperates with BIM to stimulate intramolecular activation of monomeric BAX prior to membrane association. BAX α8 mobility and proline 168-mediated allostery are critical determinants for 2t-hexadecenal synergy with BAX and BIM, as is alkenal length to stimulate BAF function. Collectively, this work imparts detailed molecular insights into how pro-apoptotic BCL-2 proteins and bioactive lipids non-covalently cooperate to initiate the mitochondrial pathway of apoptosis with implications for biological and therapeutic regulation.

Mitochondria maintain a biochemical environment that cooperates with BH3-only proteins (e.g., BIM) to potentiate BAX activation, the key event to initiate physiological and pharmacological forms of apoptosis. The sphingosine-1-phosphate metabolite 2-trans-hexadecenal (2t-hexadecenal) is one such component described to support BAX activation, but molecular mechanisms remain largely unknown. Here, we utilize complementary biochemical and biophysical techniques to reveal that 2t-hexadecenal non-covalently interacts with BAX, and cooperates with BIM to stimulate early-activation steps of monomeric BAX. Integrated structural and computational approaches reveal 2t-hexadecenal binds an undefined region - a hydrophobic cavity formed by core-facing residues of α5, α6, and gated by α8 - we now term the "BAX actuating funnel" (BAF). We define alkenal length and α8 mobility as critical determinants for 2t-hexadecenal synergy with BIM and BAX, and demonstrate that proline 168 allosterically regulates BAF function. Collectively, this work imparts detailed molecular insights advancing our fundamental knowledge of BAX regulation and identifies a regulatory region with implications for biological and therapeutic opportunities.

Abstract Deubiquitinase‐targeting chimera (DUBTAC) is a promising technology for inducing targeted protein stabilization (TPS). Despite its therapeutic potential, very few proteins have been stabilized by DUBTACs to date. The limited applicability of this technology is likely due to the modest DUBTAC‐induced protein stabilization effect, and the scarcity of effective deubiquitinase ligands that can be harnessed for DUBTAC development. Here, we report the discovery of MS7829 and MS8588, the first‐in‐class DUBTACs of cGAS, a key component of the cGAS‐STING pathway. While these DUBTACs are based on a cGAS inhibitor, they effectively stabilized cGAS and activated the cGAS/STING/IRF3 signaling. To develop these cGAS DUBTACs, we optimized EN523, an OTUB1 covalent ligand, into an improved ligand, MS5105. We validated MS5105 by generating a MS5105‐based CFTR DUBTAC, which was approximately 10‐fold more effective in stabilizing the ΔF508‐CFTR mutant protein than the previously reported EN523‐based CFTR DUBTAC. Overall, this work advances the DUBTAC technology for TPS.