title: Structure of the apoptosome: mechanistic insights into activation of an initiator caspase from Drosophila.
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.
authors: Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China;
authors: Yuxuan
authors: Y
authors: Pang
authors: Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors: Xiao-chen
authors: XC
authors: Bai
authors: Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China;
authors: Chuangye
authors: C
authors: Yan
authors: Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China;
authors: Qi
authors: Q
authors: Hao
authors: Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China;
authors: Zheqin
authors: Z
authors: Chen
authors: Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China;
authors: Jia-Wei
authors: JW
authors: Wang
authors: Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom shi-lab@tsinghua.edu.cn scheres@mrc-lmb.cam.ac.uk.
authors: Sjors H W
authors: SH
authors: Scheres
authors: Ministry of Education Protein Science Laboratory, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, School of Medicine, Tsinghua University, Beijing 100084, China; shi-lab@tsinghua.edu.cn scheres@mrc-lmb.cam.ac.uk.
authors: Yigong
authors: Y
authors: Shi
mesh_terms: D000818:Animals; D053478:Apoptosomes / Q000737:chemistry* / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D004330:Drosophila / Q000201:enzymology*; D029721:Drosophila Proteins / Q000378:metabolism; D004789:Enzyme Activation; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D053478:Apoptosomes; D029721:Drosophila Proteins; D020169:Caspases
keywords: Dark; Dronc; apoptosis; caspase activation; cryo-EM structure; programmed cell death
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