scholarly journals Pore formation by dimeric Bak and Bax: an unusual pore?

2017 ◽  
Vol 372 (1726) ◽  
pp. 20160218 ◽  
Author(s):  
Rachel T. Uren ◽  
Sweta Iyer ◽  
Ruth M. Kluck
Keyword(s):  
Outer Membrane ◽  
Pore Formation ◽  
Transmembrane Domain ◽  
Apoptotic Cell ◽  
Hydrophobic Surface ◽  
Mitochondrial Pathway ◽  
Membrane Curvature ◽  
Basic Unit ◽  
Mitochondrial Outer Membrane ◽  
Membrane Pores

Apoptotic cell death via the mitochondrial pathway occurs in all vertebrate cells and requires the formation of pores in the mitochondrial outer membrane. Two Bcl-2 protein family members, Bak and Bax, form these pores during apoptosis, and how they do so has been investigated for the last two decades. Many of the conformation changes that occur during their transition to pore-forming proteins have now been delineated. Notably, biochemical, biophysical and structural studies indicate that symmetric homodimers are the basic unit of pore formation. Each dimer contains an extended hydrophobic surface that lies on the outer membrane, and is anchored at either end by a transmembrane domain. Membrane-remodelling events such as positive membrane curvature have been reported to accompany apoptotic pore formation, suggesting Bak and Bax form lipidic pores rather than proteinaceous pores. However, it remains unclear how symmetric dimers assemble to porate the membrane. Here, we review how clusters of dimers and their lipid-mediated interactions provide a molecular explanation for the heterogeneous assemblies of Bak and Bax observed during apoptosis. This article is part of the themed issue ‘Membrane pores: from structure and assembly, to medicine and technology’.

scholarly journals Mitochondrial Outer Membrane Proteins Assist Bid in Bax-mediated Lipidic Pore Formation

2009 ◽  
Vol 20 (8) ◽  
pp. 2276-2285 ◽  
Author(s):  
Blanca Schafer ◽  
Joel Quispe ◽  
Vineet Choudhary ◽  
Jerry E. Chipuk ◽  
Teddy G. Ajero ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Pore Formation ◽  
Outer Membrane Proteins ◽  
Mitochondrial Outer Membrane ◽  
Outer Membranes ◽  
Mitochondrial Outer Membrane Permeabilization ◽  
In Vitro Systems ◽  
Large Round ◽  
Key Features

Mitochondrial outer membrane permeabilization (MOMP) is a critical step in apoptosis and is regulated by Bcl-2 family proteins. In vitro systems using cardiolipin-containing liposomes have demonstrated the key features of MOMP induced by Bax and cleaved Bid; however, the nature of the “pores” and how they are formed remain obscure. We found that mitochondrial outer membranes contained very little cardiolipin, far less than that required for liposome permeabilization, despite their responsiveness to Bcl-2 family proteins. Strikingly, the incorporation of isolated mitochondrial outer membrane (MOM) proteins into liposomes lacking cardiolipin conferred responsiveness to cleaved Bid and Bax. Cardiolipin dependence was observed only when permeabilization was induced with cleaved Bid but not with Bid or Bim BH3 peptide or oligomerized Bax. Therefore, we conclude that MOM proteins specifically assist cleaved Bid in Bax-mediated permeabilization. Cryoelectron microscopy of cardiolipin-liposomes revealed that cleaved Bid and Bax produced large round holes with diameters of 25–100 nm, suggestive of lipidic pores. In sum, we propose that activated Bax induces lipidic pore formation and that MOM proteins assist cleaved Bid in this process in the absence of cardiolipin.

scholarly journals Apoptotic pore formation is associated with in-plane insertion of Bak or Bax central helices into the mitochondrial outer membrane

2014 ◽  
Vol 111 (39) ◽  
pp. E4076-E4085 ◽  
Author(s):  
Dana Westphal ◽  
Grant Dewson ◽  
Marie Menard ◽  
Paul Frederick ◽  
Sweta Iyer ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Pore Formation ◽  
Mitochondrial Outer Membrane

scholarly journals Inner but Not Outer Membrane Leaflets Control the Transition from Glycosylphosphatidylinositol-anchored Influenza Hemagglutinin-induced Hemifusion to Full Fusion

1997 ◽  
Vol 136 (5) ◽  
pp. 995-1005 ◽  
Author(s):  
Grigory B. Melikyan ◽  
Sofya A. Brener ◽  
Dong C. Ok ◽  
Fredric S. Cohen
Keyword(s):  
Outer Membrane ◽  
Negative Curvature ◽  
Pore Formation ◽  
Transmembrane Domain ◽  
Positive Curvature ◽  
Fusion Pore ◽  
Spontaneous Curvature ◽  
Wild Type ◽  
Influenza Hemagglutinin ◽  
Fusion Pores

Cells that express wild-type influenza hemagglutinin (HA) fully fuse to RBCs, while cells that express the HA-ectodomain anchored to membranes by glycosylphosphatidylinositol, rather than by a transmembrane domain, only hemifuse to RBCs. Amphipaths were inserted into inner and outer membrane leaflets to determine the contribution of each leaflet in the transition from hemifusion to fusion. When inserted into outer leaflets, amphipaths did not promote the transition, independent of whether the agent induces monolayers to bend outward (conferring positive spontaneous monolayer curvature) or inward (negative curvature). In contrast, when incorporated into inner leaflets, positive curvature agents led to full fusion. This suggests that fusion is completed when a lipidic fusion pore with net positive curvature is formed by the inner leaflets that compose a hemifusion diaphragm. Suboptimal fusion conditions were established for RBCs bound to cells expressing wild-type HA so that lipid but not aqueous dye spread was observed. While this is the same pattern of dye spread as in stable hemifusion, for this “stunted” fusion, lower concentrations of amphipaths in inner leaflets were required to promote transfer of aqueous dyes. Also, these amphipaths induced larger pores for stunted fusion than they generated within a stable hemifusion diaphragm. Therefore, spontaneous curvature of inner leaflets can affect formation and enlargement of fusion pores induced by HA. We propose that after the HA-ectodomain induces hemifusion, the transmembrane domain causes pore formation by conferring positive spontaneous curvature to leaflets of the hemifusion diaphragm.

scholarly journals In situ imaging of mitochondrial outer-membrane pores using atomic force microscopy

BioTechniques ◽  
2004 ◽  
Vol 37 (4) ◽  
pp. 564-573 ◽  
Author(s):  
Bradley E. Layton ◽  
AnnMarie Sastry ◽  
Christian M. Lastoskie ◽  
Martin A. Philbert ◽  
Terry J. Miller ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Outer Membrane ◽  
Mitochondrial Outer Membrane ◽  
Force Microscopy ◽  
Membrane Pores ◽  
Atomic Force ◽  
In Situ Imaging

scholarly journals Activated BAX/BAK enable mitochondrial inner membrane permeabilisation and mtDNA release during cell death

2018 ◽  
Author(s):  
Joel S Riley ◽  
Giovanni Quarato ◽  
Jonathan Lopez ◽  
Jim O’Prey ◽  
Matthew Pearson ◽  
...  
Keyword(s):  
Cell Death ◽  
Outer Membrane ◽  
Super Resolution ◽  
Mitochondrial Outer Membrane ◽  
Dependent Manner ◽  
Inner Membrane ◽  
Membrane Pores ◽  
Mitochondrial Inner Membrane ◽  
Mitochondrial Outer Membrane Permeabilisation ◽  
Resolution Imaging

AbstractDuring apoptosis, pro-apoptotic BAX and BAK are activated, causing mitochondrial outer membrane permeabilisation (MOMP), caspase activation and cell death. However, even in the absence of caspase activity, cells usually die following MOMP. Such caspase-independent cell death is accompanied by inflammation that requires mitochondrial DNA (mtDNA) activation of cGAS-STING signaling. Because the mitochondrial inner membrane is thought to remain intact during apoptosis, we sought to address how matrix mtDNA could activate the cytosolic cGAS-STING signaling pathway. Strikingly, using super-resolution imaging, we show that mtDNA is efficiently released from mitochondria following MOMP. In a temporal manner, we find that following MOMP, BAX/BAK-mediated mitochondrial outer membrane pores gradually widen over time. This allows extrusion of the mitochondrial inner membrane into the cytosol whereupon it permeablises allowing mtDNA release. Our data demonstrate that mitochondrial inner membrane permeabilisation can occur during cell death in a BAX/BAK-dependent manner. Importantly, by enabling the cytosolic release of mtDNA, inner membrane permeabilisation underpins the immunogenic effects of caspase-independent cell death.

Two isoforms of PSAP/MTCH1 share two proapoptotic domains and multiple internal signals for import into the mitochondrial outer membrane

2007 ◽  
Vol 293 (4) ◽  
pp. C1347-C1361 ◽  
Author(s):  
Violeta Lamarca ◽  
Antonio Sanz-Clemente ◽  
Rosaura Pérez-Pé ◽  
María José Martínez-Lorenzo ◽  
Nabil Halaihel ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Transmembrane Domain ◽  
Cultured Cells ◽  
Mitochondrial Protein ◽  
Transmembrane Domains ◽  
Presenilin 1 ◽  
Mitochondrial Outer Membrane ◽  
Rat Tissues ◽  
Mitochondrial Carrier ◽  
Amino Terminal

Presenilin 1-associated protein (PSAP) was first identified as a protein that interacts with presenilin 1. It was later reported that PSAP is a mitochondrial protein that induces apoptosis when overexpressed in cultured cells. PSAP is also known as mitochondrial carrier homolog 1 (Mtch1). In this study, we show that there are two proapoptotic PSAP isoforms generated by alternative splicing that differ in the length of a hydrophilic loop located between two predicted transmembrane domains. Using RT-PCR and Western blot assays, we determined that both isoforms are expressed in human and rat tissues as well as in culture cells. Our results indicate that PSAP is an integral mitochondrial outer membrane protein, although it contains a mitochondrial carrier domain conserved in several inner membrane carriers, which partially overlaps one of the predicted transmembrane segments. Deletion of this transmembrane segment impairs mitochondrial import of PSAP. Replacement of this segment with each of two transmembrane domains, with opposite membrane orientations, from an unrelated protein indicated that one of them allowed mitochondrial localization of the PSAP mutant, whereas the other one did not. Our interpretation of these results is that PSAP contains multiple mitochondrial targeting motifs dispersed along the protein but that a transmembrane domain in the correct position and orientation is necessary for membrane insertion. The amino acid sequence within this transmembrane domain may also be important. Furthermore, two independent regions in the amino terminal side of the protein are responsible for its proapoptotic activity. Possible implications of these findings in PSAP function are discussed.

Characterization of rat TOM70 as a receptor of the preprotein translocase of the mitochondrial outer membrane

2002 ◽  
Vol 115 (9) ◽  
pp. 1895-1905 ◽  
Author(s):  
Hiroyuki Suzuki ◽  
Maki Maeda ◽  
Katsuyoshi Mihara
Keyword(s):  
Outer Membrane ◽  
Transmembrane Domain ◽  
Structural Similarity ◽  
Mitochondrial Outer Membrane ◽  
Outer Membranes ◽  
Sequence Identity ◽  
Arginine Residues ◽  
Targeting Signal ◽  
Mitochondria Targeting

We cloned a ∼70 kDa rat mitochondrial outer membrane protein (OM70)with a sequence identity of 28.1% and 20.1% with N. crassa and S. cerevisiae Tom70, respectively. Even with this low sequence identity,however, the proteins share a remarkable structural similarity: they have 7-10 tetratricopeptide repeat motifs and are anchored to the outer membrane through the N-terminal transmembrane domain with the bulk portion located in the cytosol. Antibodies against OM70 inhibited import of preproteins, such as the ADP/ATP carrier and rTOM40, that use internal targeting signals but not the import of cleavable presequence-containing preproteins. Blue native gel electrophoresis and immunoprecipitation of digitoninsolubilized mitochondrial outer membranes revealed that OM70 was loosely associated with the ∼400 kDa translocase complex of the mitochondrial outer membrane, which contains rTOM22 and rTOM40. A yeast two-hybrid system demonstrated that OM70 interacted with rTOM20 and rTOM22 through the cytoplasmic domains. Thus, OM70 is a functional homologue of fungal Tom70 and functions as a receptor of the preprotein import machinery of the rat mitochondrial outer membrane. Furthermore, the N-terminal 66 residue region of OM70, which comprises a hydrophilic 41 residue N-terminal domain, a 22 residue transmembrane domain and three arginine residues, is sufficient to act as a mitochondria-targeting signal, and the arginine cluster is crucial for this function.

scholarly journals Role of MMM1 in Maintaining Mitochondrial Morphology inNeurospora crassa

2000 ◽  
Vol 11 (9) ◽  
pp. 2961-2971 ◽  
Author(s):  
Holger Prokisch ◽  
Walter Neupert ◽  
Benedikt Westermann
Keyword(s):  
Outer Membrane ◽  
Transmembrane Domain ◽  
Female Sterility ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Temperature Sensitive ◽  
Dependent Manner ◽  
Giant Mitochondria ◽  
Mitochondrial Transport ◽  
General Importance

Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interaction of the mitochondrial outer membrane with the actin cytoskeleton. We report the cloning and characterization of MMM1 of the filamentous fungus Neurospora crassa, an organism that uses microtubules for mitochondrial transport. Mutation of themmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochondria at all stages of the asexual life cycle, whereas actin filament-depolymerizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the outer membrane in a receptor-dependent manner. Our findings suggest that MMM1 is a factor of general importance for mitochondrial morphology independent of the cytoskeletal system used for mitochondrial transport.

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