title: Bax forms multispanning monomers that oligomerize to permeabilize membranes during apoptosis.
abstract: Bax promotes cell death by permeabilizing mitochondrial outer membranes by an unresolved mechanism. However, in cells lacking the gene c-myc, membrane permeabilization by Bax is blocked by changes in the mitochondria that prevent Bax oligomerization. Drug-treated c-myc null cells and cells expressing Myc were used to map the topology of Bax in membranes prior to and after mitochondrial permeabilization. Chemical labeling of single cysteine mutants of Bax using a membrane bilayer impermeant cysteine-specific modifying agent revealed that Bax inserted both the 'pore domain' (helices alpha5-alpha6), and the tail-anchor (helix alpha9) into membranes prior to oligomerization and membrane permeabilization. Additional topology changes for Bax were not required in Myc-expressing cells to promote oligomerization and cytochrome c release. Our results suggest that unlike most pore-forming proteins, Bax membrane permeabilization results from oligomerization of transmembrane monomers rather than concerted insertion of the pore domains of a preformed oligomer.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Annis
authors.forename: Erinn L
authors.initials: EL
authors.lastname: Soucie
authors.forename: Paulina J
authors.initials: PJ
authors.lastname: Dlugosz
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Cruz-Aguado
authors.forename: Linda Z
authors.initials: LZ
authors.lastname: Penn
authors.forename: Brian
authors.initials: B
authors.lastname: Leber
authors.forename: David W
authors.initials: DW
authors.lastname: Andrews
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation; D010539:Permeability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein
chemical_list: C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; C489427:MYC protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D003545:Cysteine