title: BIM-mediated membrane insertion of the BAK pore domain is an essential requirement for apoptosis.
abstract: BAK activation represents a key step during apoptosis, but how it converts into a mitochondria-permeabilizing pore remains unclear. By further delineating the structural rearrangements involved, we reveal that BAK activation progresses through a series of independent steps: BH3-domain exposure, N-terminal change, oligomerization, and membrane insertion. Employing a "BCL-XL-addiction" model, we show that neutralization of BCL-XL by the BH3 mimetic ABT-737 resulted in death only when cells were reconstituted with BCL-XL:BAK, but not BCL-2/ BCL-XL:BIM complexes. Although this resembles the indirect model, release of BAK from BCL-XL did not result in spontaneous adoption of the pore conformation. Commitment to apoptosis required association of the direct activator BIM with oligomeric BAK promoting its conversion to a membrane-inserted pore. The sequential nature of this cascade provides multiple opportunities for other BCL-2 proteins to interfere with or promote BAK activation and unites aspects of the indirect and direct activation models.
authors.affiliation: MRC Toxicology Unit, University of Leicester, Hodgkin Building, Leicester LE1 9HN, UK.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Weber
authors.forename: Nicholas
authors.initials: N
authors.lastname: Harper
authors.forename: John
authors.initials: J
authors.lastname: Schwabe
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Cohen
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D001713:Biphenyl Compounds / Q000633:toxicity; D057809:HEK293 Cells; D006801:Humans; D019169:Jurkat Cells; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism*; D009596:Nitrophenols / Q000633:toxicity; D010879:Piperazines / Q000633:toxicity; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013449:Sulfonamides / Q000633:toxicity; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C501332:ABT-737; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D001713:Biphenyl Compounds; D008565:Membrane Proteins; D009596:Nitrophenols; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D013449:Sulfonamides; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein