Structural basis for dimerization of the death effector domain of the F122A mutant of Caspase-8

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Caspase-8 is a key apoptotic protease activated via proximity-induced dimerization in the death-inducing signaling complex (DISC).
• The death effector domain (DED) of caspase-8 mediates protein-protein interactions essential for its activation.
• Understanding DED dimerization mechanisms is critical for elucidating apoptosis regulation.

Purpose of the Study:

• To elucidate the structural basis of caspase-8 DED dimerization.
• To investigate the role of DED dimerization in the formation of death effector filaments (DEFs) and apoptosis.
• To understand how DED dimerization impacts full-length caspase-8 activation.

Main Methods:

• X-ray crystallography to determine the structures of dimeric caspase-8 DED mutants.
• Site-directed mutagenesis to disrupt DED dimerization.
• Cell-based assays to assess DEF formation and apoptosis induction.

Main Results:

• Two crystal structures of dimeric caspase-8 F122A mutant DEDs revealed a novel domain-swapped dimerization.
• Mutations disrupting DED dimerization abrogated DEF formation and apoptosis induced by overexpressed DEDs.
• Dimerization-disrupting mutations impaired full-length caspase-8 activation and the downstream apoptosis cascade.

Conclusions:

• The study provides novel structural insights into caspase-8 DED domain-swapped dimerization.
• DED dimerization is essential for both DEF formation and the activation of caspase-8 and subsequent apoptosis.
• These findings enhance understanding of procaspase-8 activation mechanisms within the DISC and DEFs.