Cryo-EM Structure of Caspase-8 Tandem DED Filament Reveals Assembly and Regulation Mechanisms of the Death-Inducing...

Area of Science:

• Molecular Biology
• Structural Biology
• Immunology

Background:

• Caspase-8 activation is crucial for programmed cell death (apoptosis) and inflammatory responses.
• Activation occurs via the death-inducing signaling complex (DISC) and the inflammasome adaptor ASC.
• The tandem death effector domain (tDED) of caspase-8 mediates its assembly with FADD and ASC.

Purpose of the Study:

• To determine the three-dimensional structure of the caspase-8 tDED filament.
• To elucidate the molecular mechanisms of caspase-8 assembly and regulation.
• To understand how inhibitors cFLIP and MC159 modulate caspase-8 activity.

Main Methods:

• Cryoelectron microscopy (cryo-EM) was used to determine the tDED filament structure.
• Structure-based mutagenesis was employed to validate assembly interfaces in vitro and in cellular contexts.
• Fas-induced apoptosis and ASC-mediated caspase-8 recruitment assays were performed in cells.

Main Results:

• The cryo-EM structure revealed extensive assembly interfaces, challenging the linear DED chain model.
• Caspase-8 tDED utilizes quasi-equivalent contacts for filament assembly.
• Structural analysis identified interaction surfaces with FADD and distinct regulatory mechanisms for cFLIP (comingling) and MC159 (capping).

Conclusions:

• The tDED filament structure provides a new framework for understanding caspase-8 activation.
• The findings clarify how caspase-8 interacts with FADD and ASC, and how it is regulated by cFLIP and MC159.
• This structural insight is vital for dissecting apoptosis and inflammasome signaling pathways.