Abstract
Apoptosis is executed by a cascade of caspase activation. The autocatalytic activation of an initiator caspase, exemplified by caspase-9 in mammals or its ortholog, Dronc, in fruit flies, is facilitated by a multimeric adaptor complex known as the apoptosome. The underlying mechanism by which caspase-9 or Dronc is activated by the apoptosome remains unknown. Here we report the electron cryomicroscopic (cryo-EM) structure of the intact apoptosome from Drosophila melanogaster at 4.0 Å resolution. Analysis of the Drosophila apoptosome, which comprises 16 molecules of the Dark protein (Apaf-1 ortholog), reveals molecular determinants that support the assembly of the 2.5-MDa complex. In the absence of dATP or ATP, Dronc zymogen potently induces formation of the Dark apoptosome, within which Dronc is efficiently activated. At 4.1Å resolution, the cryo-EM structure of the Dark apoptosome bound to the caspase recruitment domain (CARD) of Dronc (Dronc-CARD) reveals two stacked rings of Dronc-CARD that are sandwiched between two octameric rings of the Dark protein. The specific interactions between Dronc-CARD and both the CARD and the WD40 repeats of a nearby Dark protomer are indispensable for Dronc activation. These findings reveal important mechanistic insights into the activation of initiator caspase by the apoptosome.
Original language | English (US) |
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Pages (from-to) | 277-287 |
Number of pages | 11 |
Journal | Genes and Development |
Volume | 29 |
Issue number | 3 |
DOIs | |
State | Published - 2015 |
Keywords
- Apoptosis
- Caspase activation
- Cryo-EM structure
- Dark
- Dronc
- Programmed cell death
ASJC Scopus subject areas
- Genetics
- Developmental Biology