title: Autoactivation of procaspase-9 by Apaf-1-mediated oligomerization.
abstract: Activation of procaspase-9 by Apaf-1 in the cytochrome c/dATP-dependent pathway requires proteolytic cleavage to generate the mature caspase molecule. To elucidate the mechanism of activation of procaspase-9 by Apaf-1, we designed an in vitro Apaf-1-procaspase-9 activation system using recombinant components. Here, we show that deletion of the Apaf-1 WD-40 repeats makes Apaf-1 constitutively active and capable of processing procaspase-9 independent of cytochrome c an dATP. Apaf-1-mediated processing of procaspase-9 occurs at Asp-315 by an intrinsic autocatalytic activity of procaspase-9 itself. We provide evidence that Apaf-1 can form oligomers and may facilitate procaspase-9 autoactivation by oligomerizing its precursor molecules. Once activated, caspase-9 can initiate a caspase cascade involving the downstream executioners caspase-3, -6, and -7.
authors.affiliation: Center for Apoptosis Research, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Srinivasula
authors.forename: M
authors.initials: M
authors.lastname: Ahmad
authors.forename: T
authors.initials: T
authors.lastname: Fernandes-Alnemri
authors.forename: E S
authors.initials: ES
authors.lastname: Alnemri
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D053477:Apoptotic Protease-Activating Factor 1; D001665:Binding Sites; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D053148:Caspase 3; D053178:Caspase 6; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases; D002384:Catalysis; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation / Q000235:genetics; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000201:enzymology
chemical_list: C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D001704:Biopolymers; D003574:Cytochrome c Group; D004792:Enzyme Precursors; D011506:Proteins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; C505407:CASP3 protein, human; C505514:CASP6 protein, human; C505520:CASP7 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053178:Caspase 6; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases; D003546:Cysteine Endopeptidases