Conformational Rearrangements in the Pro-apoptotic Protein, Bax, as It Inserts into Mitochondria

Gahl, Robert F.; He, Yi; Yu, Shiqin; Tjandra, Nico

doi:10.1074/jbc.m114.593897

Cited by 66 publications

(107 citation statements)

References 36 publications

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“…An α9:α9 interface in Bak (and Bax) oligomers was demonstrated by linkage of the α9 helices after pore formation, consistent with very recent evidence of an α9:α9 interface in Bax oligomers, Figure 3a, or for cytochrome c release based on Förster resonance energy transfer (FRET) 29 and crosslinking. 67 A distinct cysteine linkage pattern along α9 was not due to a dimerization domain, but may be caused by a preferred packing surface between the helices and/or by limited rotation of α9 within oligomers.…”

Section: Discussionsupporting

confidence: 87%

“…67 Notably, Bleicken et al 67 suggested the α9:α9 interaction 'within' dimers may be anti-parallel based on a model in which the α2-α5 core dimers position on the rim of the pore rather than facing the cytosol. Although our linkage studies and the FRET studies of Gahl et al 29 show parallel interaction of the α9 helices, we may be detecting interactions 'between' dimers (as depicted in Figure 7d) and not the interactions that might occur 'within' dimers.…”

Section: Discussioncontrasting

confidence: 50%

“…29,67 Furthermore, the α6-α9 region in oligomerized Bax was found to be extended 29 and flexible. 67 Notably, Bleicken et al 67 suggested the α9:α9 interaction 'within' dimers may be anti-parallel based on a model in which the α2-α5 core dimers position on the rim of the pore rather than facing the cytosol.…”

Section: Discussionmentioning

confidence: 94%

“…The C terminus targets Bak to the MOM in healthy cells, 28 whereas the Bax C terminus is either exposed 29 or sequestered within the hydrophobic groove until apoptotic signals trigger Bax translocation. 5,30,31 The hydrophobic stretch is important, as substituting polar or charged residues decreased targeting of Bak and Bax.…”

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confidence: 99%

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Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

et al. 2015

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Bak and Bax mediate apoptotic cell death by oligomerizing and forming a pore in the mitochondrial outer membrane. Both proteins anchor to the outer membrane via a C-terminal transmembrane domain, although its topology within the apoptotic pore is not known. Cysteine-scanning mutagenesis and hydrophilic labeling confirmed that in healthy mitochondria the Bak α9 segment traverses the outer membrane, with 11 central residues shielded from labeling. After pore formation those residues remained shielded, indicating that α9 does not line a pore. Bak (and Bax) activation allowed linkage of α9 to neighboring α9 segments, identifying an α9:α9 interface in Bak (and Bax) oligomers. Although the linkage pattern along α9 indicated a preferred packing surface, there was no evidence of a dimerization motif. Rather, the interface was invoked in part by Bak conformation change and in part by BH3:groove dimerization. The α9:α9 interaction may constitute a secondary interface in Bak oligomers, as it could link BH3:groove dimers to high-order oligomers. Moreover, as high-order oligomers were generated when α9:α9 linkage in the membrane was combined with α6:α6 linkage on the membrane surface, the α6-α9 region in oligomerized Bak is flexible. These findings provide the first view of Bak carboxy terminus (C terminus) membrane topology within the apoptotic pore. Mitochondrial permeabilization during apoptosis is regulated by the Bcl-2 family of proteins. 1-3 Although the Bcl-2 homology 3 (BH3)-only members such as Bid and Bim trigger apoptosis by binding to other family members, the prosurvival members block apoptosis by sequestering their pro-apoptotic relatives. Two remaining members, Bak and Bax, form the apoptotic pore within the mitochondrial outer membrane (MOM).Bak and Bax are globular proteins comprising nine α-helices. 4,5 They are activated by BH3-only proteins binding to the α2-α5 surface groove, 6-12 or for Bax, to the α1/α6 'rear pocket'. 13 Binding triggers dissociation of the latch domain (α6-α8) from the core domain (α2-α5), together with exposure of N-terminal epitopes and the BH3 domain. 6,7,14-16 The exposed BH3 domain then binds to the hydrophobic groove in another Bak or Bax molecule to generate symmetric homodimers. 6,7,14,17,18 In addition to dimerizing, parts of activated Bak and Bax associate with the lipid bilayer. 19 In Bax, the α5 and α6 helices may insert into the MOM, 20 although recent studies indicate that they lie in-plane on the membrane surface, with the hydrophobic α5 sandwiched between the membrane and a BH3:groove dimer interface. 7,[21][22][23] The dimers can be linked via cysteine residues placed in α6, 18,24,25 and more recently via cysteine residues in either α3 or α5, 6,21 allowing detection of the higherorder oligomers associated with pore formation. 26,27 However, whether these interactions are required for high-order oligomers and pore formation remains unclear.Like most Bcl-2 members, Bak and Bax are targeted to the MOM via a hydrophobic C-terminal region. The C terminus targets Bak to the...

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Section: Discussionsupporting

confidence: 87%

Section: Discussioncontrasting

confidence: 50%

Section: Discussionmentioning

confidence: 94%

mentioning

confidence: 99%

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Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

et al. 2015

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“…Analysis of the active Bax membrane topology suggests that the TMD could play a central role in Bax oligomerization (26). Förster resonance energy transfer studies have shown that Bax forms homooligomers in the mitochondria through TMD interactions (27). Bcl-x L -mediated Bax retrotranslocation into the cytosol depends on the Bcl-x L TMD, suggesting the involvement of TMD interactions in Bax inhibition (13).…”

mentioning

confidence: 99%

Bax transmembrane domain interacts with prosurvival Bcl-2 proteins in biological membranes

Andreu-Férnández

Sancho

Genovés

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The Bcl-2 (B-cell lymphoma 2) protein Bax (Bcl-2 associated X, apoptosis regulator) can commit cells to apoptosis via outer mitochondrial membrane permeabilization. Bax activity is controlled in healthy cells by prosurvival Bcl-2 proteins. C-terminal Bax transmembrane domain interactions were implicated recently in Bax pore formation. Here, we show that the isolated transmembrane domains of Bax, Bcl-x L (B-cell lymphoma-extra large), and Bcl-2 can mediate interactions between Bax and prosurvival proteins inside the membrane in the absence of apoptotic stimuli. Bcl-2 protein transmembrane domains specifically homooligomerize and heterooligomerize in bacterial and mitochondrial membranes. Their interactions participate in the regulation of Bcl-2 proteins, thus modulating apoptotic activity. Our results suggest that interactions between the transmembrane domains of Bax and antiapoptotic Bcl-2 proteins represent a previously unappreciated level of apoptosis regulation.

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Inducible fold‐switching as a mechanism to fibrillate pro‐apoptotic BCL‐2 proteins

Morris

Tjandra

2021

Biopolymers

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Neurodegenerative diseases often are associated with cellular dysregulation that results in premature cell death or apoptosis. A common example is the accumulation of amyloid plaques that promotes the excessive expression of p38 mitogen-activated protein kinase. The increased abundance of this enzyme leads to mass phosphorylation and activation of a protein from the B-cell lymphoma 2 (BCL-2) family, BAX.BAX is the central regulatory protein for mitochondrial outer membrane permeabilization (MOMP), a poration process that commits cells to apoptosis by releasing death-propagating factors from the mitochondria. Recent reports identify a naturally occurring peptide, Humanin (HN), that could block amyloid-beta-associated neuronal apoptosis by interacting with BCL-2 proteins. We recently showed humanin interaction leads to the amyloid-like fibrillation of BAX and a second BCL-2 family member, BID. We proposed this as a novel anti-apoptotic mechanism that inhibits pro-apoptotic BCL-2 proteins from initiating MOMP by sequestering them into fibrils, a heretofore unprecedented phenomenon that involves refolding globular BCL-2 proteins rapidly into fibrils where they undergo significant alpha-helix to betasheet fold-switching. Here we seek to further characterize the fibrillation and foldswitch in conditions that are known to induce amyloid fibrillation.

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Conformational Rearrangements in the Pro-apoptotic Protein, Bax, as It Inserts into Mitochondria

Cited by 66 publications

References 36 publications

Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

Bax transmembrane domain interacts with prosurvival Bcl-2 proteins in biological membranes

Inducible fold‐switching as a mechanism to fibrillate pro‐apoptotic BCL‐2 proteins

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