Mechanistic insights into CED-4-mediated activation of CED-3

Genes Dev. 2013 Sep 15;27(18):2039-48. doi: 10.1101/gad.224428.113.


Programmed cell death in Caenorhabditis elegans requires activation of the caspase CED-3, which strictly depends on CED-4. CED-4 forms an octameric apoptosome, which binds the CED-3 zymogen and facilitates its autocatalytic maturation. Despite recent advances, major questions remain unanswered. Importantly, how CED-4 recognizes CED-3 and how such binding facilitates CED-3 activation remain completely unknown. Here we demonstrate that the L2' loop of CED-3 directly binds CED-4 and plays a major role in the formation of an active CED-4-CED-3 holoenzyme. The crystal structure of the CED-4 apoptosome bound to the L2' loop fragment of CED-3, determined at 3.2 Å resolution, reveals specific interactions between a stretch of five hydrophobic amino acids from CED-3 and a shallow surface pocket within the hutch of the funnel-shaped CED-4 apoptosome. Structure-guided biochemical analysis confirms the functional importance of the observed CED-4-CED-3 interface. Structural analysis together with published evidence strongly suggest a working model in which two molecules of CED-3 zymogen, through specific recognition, are forced into the hutch of the CED-4 apoptosome, consequently undergoing dimerization and autocatalytic maturation. The mechanism of CED-3 activation represents a major revision of the prevailing model for initiator caspase activation.

Keywords: CED-3; CED-4; apoptosis; caspase activation; programmed cell death (PCD).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids / chemistry
  • Animals
  • Caenorhabditis elegans
  • Caenorhabditis elegans Proteins / chemistry*
  • Caenorhabditis elegans Proteins / metabolism*
  • Calcium-Binding Proteins / chemistry*
  • Calcium-Binding Proteins / metabolism*
  • Caspases / chemistry*
  • Caspases / metabolism*
  • Crystallization
  • Enzyme Activation
  • Models, Molecular*
  • Protein Binding
  • Protein Stability
  • Protein Structure, Quaternary


  • Amino Acids
  • Caenorhabditis elegans Proteins
  • Calcium-Binding Proteins
  • Ced-4 protein, C elegans
  • Caspases
  • ced-3 protein, C elegans