title: Apoptotic pore formation is associated with in-plane insertion of Bak or Bax central helices into the mitochondrial outer membrane.
abstract: The pivotal step on the mitochondrial pathway to apoptosis is permeabilization of the mitochondrial outer membrane (MOM) by oligomers of the B-cell lymphoma-2 (Bcl-2) family members Bak or Bax. However, how they disrupt MOM integrity is unknown. A longstanding model is that activated Bak and Bax insert two α-helices, α5 and α6, as a hairpin across the MOM, but recent insights on the oligomer structures question this model. We have clarified how these helices contribute to MOM perforation by determining that, in the oligomers, Bak α5 (like Bax α5) remains part of the protein core and that a membrane-impermeable cysteine reagent can label cysteines placed at many positions in α5 and α6 of both Bak and Bax. The results are inconsistent with the hairpin insertion model but support an in-plane model in which α5 and α6 collapse onto the membrane and insert shallowly to drive formation of proteolipidic pores.
authors.affiliation: Molecular Genetics of Cancer Division, Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and.
authors.forename: Dana
authors.initials: D
authors.lastname: Westphal
authors.affiliation: Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and Cell Signalling and Cell Death Division, and.
authors.forename: Grant
authors.initials: G
authors.lastname: Dewson
authors.affiliation: Molecular Genetics of Cancer Division.
authors.forename: Marie
authors.initials: M
authors.lastname: Menard
authors.affiliation: Molecular Genetics of Cancer Division.
authors.forename: Paul
authors.initials: P
authors.lastname: Frederick
authors.affiliation: Molecular Genetics of Cancer Division, Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and.
authors.forename: Sweta
authors.initials: S
authors.lastname: Iyer
authors.affiliation: Molecular Genetics of Cancer Division.
authors.forename: Ray
authors.initials: R
authors.lastname: Bartolo
authors.affiliation: Molecular Genetics of Cancer Division.
authors.forename: Leonie
authors.initials: L
authors.lastname: Gibson
authors.affiliation: Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC 3052, Australia;
authors.forename: Peter E
authors.initials: PE
authors.lastname: Czabotar
authors.affiliation: School of Molecular Sciences, La Trobe Institute for Molecular Sciences, La Trobe University, Melbourne, VIC 3086, Australia.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Smith
authors.affiliation: Molecular Genetics of Cancer Division, Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and adams@wehi.edu.au kluck@wehi.edu.au.
authors.forename: Jerry M
authors.initials: JM
authors.lastname: Adams
authors.affiliation: Molecular Genetics of Cancer Division, Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia; and adams@wehi.edu.au kluck@wehi.edu.au.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Kluck
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D003545:Cysteine / Q000737:chemistry; D006801:Humans; D051379:Mice; D051336:Mitochondrial Membranes / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013267:Stilbenes; D013439:Sulfhydryl Reagents; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: C090885:4-acetamido-4'-((iodoacetyl)amino)stilbene-2,2'-disulfonate; C494772:BAK1 protein, human; C494826:BAX protein, human; D011994:Recombinant Proteins; D013267:Stilbenes; D013439:Sulfhydryl Reagents; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D003545:Cysteine
keywords: cell death; cysteine-scanning mutagenesis; membrane pores; mitochondrial permeabilization; protein-membrane topology