Bax dimerizes via a symmetric BH3:groove interface during apoptosis.
During apoptotic cell death, Bax and Bak change conformation and homo-oligomerize to permeabilize mitochondria. We recently reported that Bak homodimerizes via an interaction between the BH3 domain and hydrophobic surface groove, that this BH3:groove interaction is symmetric, and that symmetric dimers can be linked via the α6-helices to form the high order oligomers thought responsible for pore formation. We now show that Bax also dimerizes via a BH3:groove interaction after apoptotic signaling in cells and in mitochondrial fractions. BH3:groove dimers of Bax were symmetric as dimers but not higher order oligomers could be linked by cysteine residues placed in both the BH3 and groove. The BH3:groove interaction was evident in the majority of mitochondrial Bax after apoptotic signaling, and correlated strongly with cytochrome c release, supporting its central role in Bax function. A second interface between the Bax α6-helices was implicated by cysteine linkage studies, and could link dimers to higher order oligomers. We also found that a population of Bax:Bak heterodimers generated during apoptosis formed via a BH3:groove interaction, further demonstrating that Bax and Bak oligomerize via similar mechanisms. These findings highlight the importance of BH3:groove interactions in apoptosis regulation by the Bcl-2 protein family.
The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia.
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Dewson
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Frederick
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Hockings
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Tan
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Kratina
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Kluck
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002461:Cell Line, Transformed; D045304:Cytochromes c / Q000235:genetics / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000502:physiology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
C494772:BAK1 protein, human; C494826:BAX protein, human; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c