title: The activator of apoptosis Smac-DIABLO acts as a tetramer in solution.
abstract: Smac-DIABLO in its mature form (20.8 kDa) binds to baculoviral IAP repeat (BIR) domains of inhibitor of apoptosis proteins (IAPs) releasing their inhibitory effects on caspases, thus promoting cell death. Despite its apparent molecular mass (∼100 kDa), Smac-DIABLO was held to be a dimer in solution, simultaneously targeting two distinct BIR domains. We report an extensive biophysical characterization of the protein alone and in complex with the X-linked IAP (XIAP)-BIR2-BIR3 domains. Our data show that Smac-DIABLO adopts a tetrameric assembly in solution and that the tetramer is able to bind two BIR2-BIR3 pairs of domains. Our small-angle x-ray scattering-based tetrameric model of Smac-DIABLO/BIR2-BIR3 highlights some conformational freedom of the complex that may be related to optimization of IAPs binding.
authors: Dipartimento di Bioscienze, Università di Milano, Milano, Italy; CNR-IBF, Istituto di Biofisica, Milano, Italy.
authors: Eloise
authors: E
authors: Mastrangelo
authors: CNRS - UMR 8619, Orsay, France; Université Paris-Sud, Orsay, France. Electronic address: patrice.vachette@u-psud.fr.
authors: Patrice
authors: P
authors: Vachette
authors: Dipartimento di Bioscienze, Università di Milano, Milano, Italy.
authors: Federica
authors: F
authors: Cossu
authors: Dipartimento di Bioscienze, Università di Milano, Milano, Italy.
authors: Francesca
authors: F
authors: Malvezzi
authors: Dipartimento di Bioscienze, Università di Milano, Milano, Italy.
authors: Martino
authors: M
authors: Bolognesi
authors: Dipartimento di Bioscienze, Università di Milano, Milano, Italy; CNR-IBF, Istituto di Biofisica, Milano, Italy. Electronic address: mario.milani@unimi.it.
authors: Mario
authors: M
authors: Milani
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D012996:Solutions; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D012996:Solutions; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human
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