Molecular determinants of caspase-9 activation by the Apaf-1 apoptosome

Proc Natl Acad Sci U S A. 2014 Nov 18;111(46):16254-61. doi: 10.1073/pnas.1418000111. Epub 2014 Oct 13.


Autocatalytic activation of an initiator caspase triggers the onset of apoptosis. In dying cells, caspase-9 activation is mediated by a multimeric adaptor complex known as the Apaf-1 apoptosome. The molecular mechanism by which caspase-9 is activated by the Apaf-1 apoptosome remains largely unknown. Here we demonstrate that the previously reported 1:1 interaction between Apaf-1 caspase recruitment domain (CARD) and caspase-9 CARD is insufficient for the activation of caspase-9. Rather, formation of a multimeric CARD:CARD assembly between Apaf-1 and caspase-9, which requires three types of distinct interfaces, underlies caspase-9 activation. Importantly, an additional surface area on the multimeric CARD assembly is essential for caspase-9 activation. Together, these findings reveal mechanistic insights into the activation of caspase-9 by the Apaf-1 apoptosome and support the induced conformation model for initiator caspase activation by adaptor complexes.

Keywords: CARD; apoptosis; caspase activation; induced proximity; mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis Regulatory Proteins / chemistry*
  • Apoptosis Regulatory Proteins / genetics
  • Apoptosis Regulatory Proteins / metabolism
  • Apoptosomes / metabolism*
  • Caspase 9 / chemistry*
  • Caspase 9 / metabolism
  • Catalysis
  • Enzyme Activation
  • Humans
  • Hydrogen Bonding
  • In Vitro Techniques
  • Lysine / chemistry
  • Models, Chemical
  • Models, Molecular
  • Mutagenesis, Site-Directed
  • Protein Conformation
  • Protein Interaction Mapping
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism


  • APIP protein, human
  • Apoptosis Regulatory Proteins
  • Apoptosomes
  • Recombinant Fusion Proteins
  • CASP9 protein, human
  • Caspase 9
  • Lysine

Associated data

  • PDB/4RHW