title: Changes in Apaf-1 conformation that drive apoptosome assembly.
abstract: Apoptosome assembly is highly regulated in the intrinsic cell death pathway. To better understand this step, we created an improved model of the human apoptosome using a crystal structure of full length Apaf-1 and a single particle, electron density map at ~9.5 Å resolution. The apoptosome model includes N-terminal domains of Apaf-1, cognate β-propellers, and cytochrome c. A direct comparison of Apaf-1 in the apoptosome and as a monomer reveals conformational changes that occur during the first two steps of assembly. This includes an induced-fit mechanism for cytochrome c binding to regulatory β-propellers, which is dependent on shape and charge complementarity, and a large rotation of the nucleotide binding module during nucleotide exchange. These linked conformational changes create an extended Apaf-1 monomer and drive apoptosome assembly. Moreover, the N-terminal CARD in the inactive Apaf-1 monomer is not shielded from other proteins by β-propellers. Hence, the Apaf-1 CARD may be free to interact with a procaspase-9 CARD either before or during apoptosome assembly. Irrespective of the timing, the end product of assembly is a holo-apoptosome with an acentric CARD-CARD disk and tethered pc-9 catalytic domains. Subsequent activation of pc-9 leads to a proteolytic cascade and cell death.
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
authors.forename: Shujun
authors.initials: S
authors.lastname: Yuan
authors.forename: Maya
authors.initials: M
authors.lastname: Topf
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Reubold
authors.forename: Susanne
authors.initials: S
authors.lastname: Eschenburg
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Akey
mesh_terms: D053478:Apoptosomes / Q000737:chemistry / Q000378:metabolism*; D053477:Apoptotic Protease-Activating Factor 1 / Q000737:chemistry* / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: C506592:APAF1 protein, human; D053478:Apoptosomes; D053477:Apoptotic Protease-Activating Factor 1; D045304:Cytochromes c