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Updated: Jan 21, 2026

Author Spotlight: Evaluating Biophysical Assays for Characterizing PROTACS Ternary Complexes
Published on: January 12, 2024
Proteolysis Targeting Chimeras for the Selective Degradation of Mcl-1/Bcl-2 Derived from Nonselective Target Binding
Abstract:
Proteolysis targeting chimera (PROTAC) recruits an E3 ligase to a target protein to induce its ubiquitination and subsequent degradation. We reported success in the development of two PROTACs (C3 and C5) that potently and selectively induce the degradation of Mcl-1 and Bcl-2 (DC50 = 0.7 and 3.0 μM), respectively, by introducing the E3 ligase cereblon-binding ligand pomalidomide to Mcl-1/Bcl-2 dual inhibitors S1-6 and Nap-1 with micromolar-range affinity. C3-induced Mcl-1 ubiquitination translated into much more lethality in Mcl-1-dependent H23 cells than the most potent Mcl-1 occupancy-based inhibitor A-1210477 with nanomolar-range affinity. Moreover, structure-activity relationship analysis and molecular dynamic simulations discovered the structural basis for turning nonselective or promiscuous Bcl-2 family ligands into selective PROTACs. C3 and C5 exhibited reversible depletion in living cells, which provides a new potent toolkit for gain-of-function studies to probe the dynamic roles of Bcl-2 and Mcl-1 in apoptosis networks.
Insights
Two novel proteolysis targeting chimeras (PROTACs), C3 and C5, effectively degrade Mcl-1 and Bcl-2 proteins. These PROTACs offer a powerful new tool for studying protein function and apoptosis.
Area of Science:
- Biochemistry
- Molecular Biology
- Drug Discovery
Background:
- Proteolysis targeting chimeras (PROTACs) leverage E3 ligases for targeted protein degradation.
- Mcl-1 and Bcl-2 are key regulators of apoptosis, making them important therapeutic targets.
Purpose of the Study:
- To develop novel PROTACs targeting Mcl-1 and Bcl-2.
- To investigate the mechanism and efficacy of these PROTACs in protein degradation and cellular lethality.
- To elucidate the structural basis for selective PROTAC development.
Main Methods:
- Synthesis and characterization of PROTACs C3 and C5.
- In vitro and cellular assays to measure protein degradation (DC50 values).
- Structure-activity relationship analysis and molecular dynamic simulations.
Main Results:
- PROTACs C3 and C5 potently and selectively degraded Mcl-1 and Bcl-2, respectively.
- C3-induced degradation resulted in greater cell lethality compared to a known inhibitor.
- Structural insights were gained into converting nonselective ligands into selective PROTACs.
Conclusions:
- C3 and C5 represent effective PROTACs for Mcl-1 and Bcl-2 degradation.
- These PROTACs provide a valuable toolkit for functional studies of apoptosis regulators.
- The study offers a structural framework for designing selective PROTACs.
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