To trigger apoptosis, Bak exposes its BH3 domain and homodimerizes via BH3:groove interactions.
The Bcl-2 relative Bak is thought to drive apoptosis by forming homo-oligomers that permeabilize mitochondria, but how it is activated and oligomerizes is unclear. To clarify these pivotal steps toward apoptosis, we have characterized multiple random loss-of-function Bak mutants and explored the mechanism of Bak conformation change during apoptosis. Single missense mutations located to the alpha helix 2-5 region of Bak, with most altering the BH3 domain or hydrophobic groove (BH1 domain). Loss of function invariably corresponded to impaired ability to oligomerize. An essential early step in Bak activation was shown to be exposure of the BH3 domain, which became reburied in dimers. We demonstrate that oligomerization involves insertion of the BH3 domain of one Bak molecule into the groove of another and may produce symmetric Bak dimers. We conclude that this BH3:groove interaction is essential to nucleate Bak oligomerization, which in turn is required for its proapoptotic function.
Dewson
Grant
G
Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Melbourne, Victoria 3050, Australia.
Kratina
Tobias
T
Sim
Huiyan W
HW
Puthalakath
Hamsa
H
Adams
Jerry M
JM
Colman
Peter M
PM
Kluck
Ruth M
RM
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D002478:Cells, Cultured; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D004220:Disulfides; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein