title: The Apaf-1 apoptosome induces formation of caspase-9 homo- and heterodimers with distinct activities.
abstract: According to dogma, initiator caspases are activated through proximity-induced homodimerization, but some studies infer that during apoptosis caspase-9 may instead form a holoenzyme with the Apaf-1 apoptosome. Using several biochemical approaches, including a novel site-specific crosslinking technique, we provide the first direct evidence that procaspase-9 homodimerizes within the apoptosome, markedly increasing its avidity for the complex and inducing selective intramolecular cleavage at Asp-315. Remarkably, however, procaspase-9 could also bind via its small subunit to the NOD domain in Apaf-1, resulting in the formation of a heterodimer that more efficiently activated procaspase-3. Following cleavage, the intersubunit linker (and associated conformational changes) in caspase-9-p35/p12 inhibited its ability to form homo- and heterodimers, but feedback cleavage by caspase-3 at Asp-330 removed the linker entirely and partially restored activity to caspase-9-p35/p10. Thus, the apoptosome mediates the formation of caspase-9 homo- and heterodimers, both of which are impacted by cleavage and contribute to its overall function.
authors.affiliation: Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas 78957, USA.|Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Chu-Chiao
authors.initials: CC
authors.lastname: Wu
authors.affiliation: Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas 78957, USA.
authors.forename: Sunhee
authors.initials: S
authors.lastname: Lee
authors.affiliation: Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Malladi
authors.affiliation: Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas 78957, USA.|Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Miao-Der
authors.initials: MD
authors.lastname: Chen
authors.affiliation: Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas 78957, USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Mastrandrea
authors.affiliation: Bioengineering Department, Santa Clara University, Santa Clara, California 95053, USA.
authors.forename: Zhiwen
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Smithville, Texas 78957, USA.
authors.forename: Shawn B
authors.initials: SB
authors.lastname: Bratton
mesh_terms: D000818:Animals; D017209:Apoptosis; D053478:Apoptosomes / Q000378:metabolism*; D053477:Apoptotic Protease-Activating Factor 1 / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D019281:Dimerization; D051379:Mice; D010770:Phosphotransferases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D061987:Sf9 Cells; D018411:Spodoptera; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: C506593:Apaf1 protein, mouse; D053478:Apoptosomes; D053477:Apoptotic Protease-Activating Factor 1; C492236:Cdk5r1 protein, mouse; D025521:Tumor Suppressor Proteins; D010770:Phosphotransferases; D011494:Protein Kinases; C496849:Cdk2ap1 protein, mouse; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9