Dipeptidyl peptidase 9 sets a threshold for CARD8 inflammasome formation by sequestering its active C-terminal...

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• CARD8 is an inflammasome sensor detecting danger signals.
• CARD8 interacts with dipeptidyl peptidases DPP8 and 9 (DPP8/9).
• CARD8 and NLRP1 inflammasomes share similarities in autoprocessing and DPP8/9 binding.

Purpose of the Study:

• To elucidate the structural basis of CARD8 regulation by DPP9.
• To understand how DPP8/9 inhibitors activate the CARD8 inflammasome.
• To investigate the interaction between CARD8, DPP9, and inhibitors.

Main Methods:

• Cryoelectron microscopy (cryo-EM) to determine complex structures.
• Biochemical assays to study protein interactions.
• Cell-based experiments to assess inflammasome activation.

Main Results:

• Cryo-EM revealed a repressive ternary complex of DPP9, full-length CARD8, and CARD8 C-terminal fragment (CARD8-CT).
• CARD8-CT does not directly bind the DPP8/9 active site and is not displaced by Val-boroPro (VbP).
• DPP8/9 inhibitors activate CARD8 by promoting N-terminal degradation and weakening ternary complex stability.

Conclusions:

• DPP8/9 inhibitors activate the CARD8 inflammasome through indirect mechanisms.
• Understanding CARD8-DPP9 interactions provides insights into inflammasome regulation.
• Targeting DPP8/9 offers a potential strategy for modulating immune responses.