Mechanistic insights into caspase-9 activation by the structure of the apoptosome holoenzyme

Yini Li, Mengying Zhou, Qi Hu, Xiao Chen Bai, Weiyun Huang, Sjors H.W. Scheres, Yigong Shi

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


Mammalian intrinsic apoptosis requires activation of the initiator caspase-9, which then cleaves and activates the effector caspases to execute cell killing. The heptameric Apaf-1 apoptosome is indispensable for caspase-9 activation by together forming a holoenzyme. The molecular mechanism of caspase-9 activation remains largely enigmatic. Here, we report the cryoelectron microscopy (cryo-EM) structure of an apoptotic holoenzyme and structure-guided biochemical analyses. The caspase recruitment domains (CARDs) of Apaf-1 and caspase-9 assemble in two different ways: a 4:4 complex docks onto the central hub of the apoptosome, and a 2:1 complex binds the periphery of the central hub. The interface between the CARD complex and the central hub is required for caspase-9 activation within the holoenzyme. Unexpectedly, the CARD of free caspase-9 strongly inhibits its proteolytic activity. These structural and biochemical findings demonstrate that the apoptosome activates caspase-9 at least in part through sequestration of the inhibitory CARD domain.

Original languageEnglish (US)
Pages (from-to)1542-1547
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number7
StatePublished - Feb 14 2017


  • Apoptosome
  • Caspase activation
  • Caspase-9
  • Cryo-EM
  • Holoenzyme

ASJC Scopus subject areas

  • General


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