Structural Insights into PROTAC-Mediated Degradation of Bcl-xL

Area of Science:

• Biochemistry
• Structural Biology
• Oncology

Background:

• Bcl-xL is a key regulator of cancer cell survival and a target for cancer therapy.
• Bcl-xL inhibitors are FDA-approved, but Proteolysis Targeting Chimeras (PROTACs) offer potential for enhanced efficacy and reduced toxicity.
• No ternary complex structures of Bcl-xL with a PROTAC and E3 ligase have been determined.

Purpose of the Study:

• To design, characterize, and determine the X-ray structure of a VHL E3 ligase-recruiting Bcl-xL PROTAC degrader.
• To elucidate the structural basis for PROTAC-mediated degradation of Bcl-xL.
• To identify novel interactions guiding the rational design of bifunctional molecules.

Main Methods:

• PROTAC design and synthesis.
• Protein expression and purification.
• X-ray crystallography at 1.9 Å resolution.
• Structural analysis of the heterotetrameric complex.

Main Results:

• Successful design and characterization of a VHL E3 ligase-recruiting Bcl-xL PROTAC.
• Determination of the 1.9 Å X-ray structure of the (ElonginB:ElonginC:VHL):PROTAC:Bcl-xL complex.
• Identification of extensive novel interactions between the E3 ligase, PROTAC, and Bcl-xL.

Conclusions:

• The determined structure provides critical insights into the mechanism of PROTAC-mediated degradation of Bcl-xL.
• This work highlights the complexity of designing bifunctional molecules targeting composite interfaces.
• The findings pave the way for improved rational design of PROTACs for cancer therapy.