Structure of the apoptosome: mechanistic insights into activation of an initiator caspase from Drosophila
- Yuxuan Pang1,2,3,5,
- Xiao-chen Bai4,5,
- Chuangye Yan1,2,3,
- Qi Hao1,2,3,
- Zheqin Chen1,2,3,
- Jia-Wei Wang2,3,
- Sjors H.W. Scheres4 and
- Yigong Shi1,2,3
- 1Ministry of Education Protein Science Laboratory,
- 2Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences,
- 3School of Medicine, Tsinghua University, Beijing 100084, China;
- 4Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
- Corresponding authors: shi-lab{at}tsinghua.edu.cn, scheres{at}mrc-lmb.cam.ac.uk
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↵5 These authors contributed equally to this work.
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 4.1 Å 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.
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Footnotes
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Supplemental material is available for this article.
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Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.255877.114.
- Received November 13, 2014.
- Accepted December 19, 2014.
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