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Mannella C. In Silico Exploration of Alternative Conformational States of VDAC. Molecules 2023; 28:molecules28083309. [PMID: 37110543 PMCID: PMC10144127 DOI: 10.3390/molecules28083309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Revised: 04/03/2023] [Accepted: 04/06/2023] [Indexed: 04/29/2023] Open
Abstract
VDAC (Voltage-Dependent Anion-selective Channel) is the primary metabolite pore in the mitochondrial outer membrane (OM). Atomic structures of VDAC, consistent with its physiological "open" state, are β-barrels formed by 19 transmembrane (TM) β-strands and an N-terminal segment (NTERM) that folds inside the pore lumen. However, structures are lacking for VDAC's partially "closed" states. To provide clues about possible VDAC conformers, we used the RoseTTAFold neural network to predict structures for human and fungal VDAC sequences modified to mimic removal from the pore wall or lumen of "cryptic" domains, i.e., segments buried in atomic models yet accessible to antibodies in OM-bound VDAC. Predicted in vacuo structures for full-length VDAC sequences are 19-strand β-barrels similar to atomic models, but with weaker H-bonding between TM strands and reduced interactions between NTERM and the pore wall. Excision of combinations of "cryptic" subregions yields β-barrels with smaller diameters, wide gaps between N- and C-terminal β-strands, and in some cases disruption of the β-sheet (associated with strained backbone H-bond registration). Tandem repeats of modified VDAC sequences also were explored, as was domain swapping in monomer constructs. Implications of the results for possible alternative conformational states of VDAC are discussed.
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Affiliation(s)
- Carmen Mannella
- Department of Physiology and Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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2
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Abstract
The evolution of the eukaryotic cell from the primal endosymbiotic event involved a complex series of adaptations driven primarily by energy optimization. Transfer of genes from endosymbiont to host and concomitant expansion (by infolding) of the endosymbiont's chemiosmotic membrane greatly increased output of adenosine triphosphate (ATP) and placed selective pressure on the membrane at the host-endosymbiont interface to sustain the energy advantage. It is hypothesized that critical functions at this interface (metabolite exchange, polypeptide import, barrier integrity to proteins and DNA) were managed by a precursor β-barrel protein ("pβB") from which the voltage-dependent anion-selective channel (VDAC) descended. VDAC's role as hub for disparate and increasingly complex processes suggests an adaptability that likely springs from a feature inherited from pβB, retained because of important advantages conferred. It is proposed that this property is the remarkable structural flexibility evidenced in VDAC's gating mechanism, a possible origin of which is discussed.
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Affiliation(s)
- Carmen A Mannella
- Department of Physiology, Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD 20201, USA
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3
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Gross LE, Spies N, Simm S, Schleiff E. Toc75-V/OEP80 is processed during translocation into chloroplasts, and the membrane-embedded form exposes its POTRA domain to the intermembrane space. FEBS Open Bio 2020; 10:444-454. [PMID: 31953987 PMCID: PMC7050246 DOI: 10.1002/2211-5463.12791] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 12/11/2019] [Accepted: 01/14/2020] [Indexed: 12/12/2022] Open
Abstract
The insertion of membrane proteins requires proteinaceous complexes in the cytoplasm, the membrane, and the lumen of organelles. Most of the required complexes have been described, while the components for insertion of β-barrel-type proteins into the outer membrane of chloroplasts remain unknown. The same holds true for the signals required for the insertion of β-barrel-type proteins. At present, only the processing of Toc75-III, the β-barrel-type protein of the central chloroplast translocon with an atypical signal, has been explored in detail. However, it has been debated whether Toc75-V/ outer envelope protein 80 (OEP80), a second protein of the same family, contains a signal and undergoes processing. To substantiate the hypothesis that Toc75-V/OEP80 is processed as well, we reinvestigated the processing in a protoplast-based assay as well as in native membranes. Our results confirm the existence of a cleavable segment. By protease protection and pegylation, we observed intermembrane space localization of the soluble N-terminal domain. Thus, Toc75-V contains a cleavable N-terminal signal and exposes its polypeptide transport-associated domains to the intermembrane space of plastids, where it likely interacts with its substrates.
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Affiliation(s)
- Lucia E. Gross
- Department of Molecular Cell Biology of PlantsGoethe UniversityFrankfurtGermany
| | - Nicole Spies
- Department of Molecular Cell Biology of PlantsGoethe UniversityFrankfurtGermany
| | - Stefan Simm
- Department of Molecular Cell Biology of PlantsGoethe UniversityFrankfurtGermany
- Frankfurt Institute for Advanced StudiesGermany
| | - Enrico Schleiff
- Department of Molecular Cell Biology of PlantsGoethe UniversityFrankfurtGermany
- Frankfurt Institute for Advanced StudiesGermany
- Buchmann Institute for Molecular Life SciencesGoethe UniversityFrankfurtGermany
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Rajmohan R, Reddy PH. Amyloid-Beta and Phosphorylated Tau Accumulations Cause Abnormalities at Synapses of Alzheimer's disease Neurons. J Alzheimers Dis 2018; 57:975-999. [PMID: 27567878 DOI: 10.3233/jad-160612] [Citation(s) in RCA: 279] [Impact Index Per Article: 46.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Amyloid-beta (Aβ) and hyperphosphorylated tau are hallmark lesions of Alzheimer's disease (AD). However, the loss of synapses and dysfunctions of neurotransmission are more directly tied to disease severity. The role of these lesions in the pathoetiological progression of the disease remains contested. Biochemical, cellular, molecular, and pathological studies provided several lines of evidence and improved our understanding of how Aβ and hyperphosphorylated tau accumulation may directly harm synapses and alter neurotransmission. In vitro evidence suggests that Aβ and hyperphosphorylated tau have both direct and indirect cytotoxic effects that affect neurotransmission, axonal transport, signaling cascades, organelle function, and immune response in ways that lead to synaptic loss and dysfunctions in neurotransmitter release. Observations in preclinical models and autopsy studies support these findings, suggesting that while the pathoetiology of positive lesions remains elusive, their removal may reduce disease severity and progression. The purpose of this article is to highlight the need for further investigation of the role of tau in disease progression and its interactions with Aβ and neurotransmitters alike.
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Affiliation(s)
- Ravi Rajmohan
- Department of Pharmacology and Neuroscience, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - P Hemachandra Reddy
- Department of Pharmacology and Neuroscience, Texas Tech University Health Sciences Center, Lubbock, TX, USA.,Department of Garrison Institute on Aging, Texas Tech University Health Sciences Center, Lubbock, TX, USA.,Department of Cell Biology & Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX, USA.,Department of Neurology, Texas Tech University Health Sciences Center, Lubbock, TX, USA.,Department of Speech, Language and Hearing Sciences, Texas Tech University Health Sciences Center, Lubbock, TX, USA
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5
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Affiliation(s)
- Marco Colombini
- Department of Biology,
University of Maryland, College
Park, Maryland 20742, United States
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Majumder S, Slabodnick M, Pike A, Marquardt J, Fisk HA. VDAC3 regulates centriole assembly by targeting Mps1 to centrosomes. Cell Cycle 2012; 11:3666-78. [PMID: 22935710 DOI: 10.4161/cc.21927] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Centrioles are duplicated during S-phase to generate the two centrosomes that serve as mitotic spindle poles during mitosis. The centrosomal pool of the Mps1 kinase is important for centriole assembly, but how Mps1 is delivered to centrosomes is unknown. Here we have identified a centrosome localization domain within Mps1 and identified the mitochondrial porin VDAC3 as a protein that binds to this region of Mps1. Moreover, we show that VDAC3 is present at the mother centriole and modulates centriole assembly by recruiting Mps1 to centrosomes.
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Affiliation(s)
- Shubhra Majumder
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
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7
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Manczak M, Reddy PH. Abnormal interaction of VDAC1 with amyloid beta and phosphorylated tau causes mitochondrial dysfunction in Alzheimer's disease. Hum Mol Genet 2012; 21:5131-46. [PMID: 22926141 DOI: 10.1093/hmg/dds360] [Citation(s) in RCA: 235] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The purpose of our study was to determine the relationship between voltage-dependent anion channel 1 protein (VDAC1) and amyloid beta (Aβ) and phosphorylated tau in Alzheimer's disease (AD). Using brain specimens from AD patients, control subjects and 6-, 12- and 24-month-old Aβ precursor protein (APP) transgenic mice, we studied VDAC1 protein levels. Further, we also studied the interaction between VDAC1 and Aβ (monomers and oligomers) and phosphorylated tau, using cortical issues from AD patients, control subjects, APP, APP/PS1 and 3XTg.AD mice. We also studied age- and VDAC1-linked, mutant APP/Aβ-induced mitochondrial dysfunction in APP and non-transgenic wild-type (WT) mice. We found progressively increased levels of VDAC1 in the cortical tissues from the brains of patients with AD, relative to control subjects, and significantly increased levels of VDAC1 in the cerebral cortices of 6-, 12- and 24-month-old APP transgenic mice, relative to the age-matched control WT mice. Interestingly, we found VDAC1 interacted with Aβ and phosphorylated tau in the brains from AD patients and from APP, APP/PS1 and 3XTg.AD mice. We found progressively increased mitochondrial dysfunction in APP mice relative to WT mice. These observations led us to conclude that VDAC1 interacts with Aβ, and phosphorylated tau may in turn block mitochondrial pores, leading to mitochondrial dysfunction in AD pathogenesis. Based on current study observations, we propose that reduced levels of VDAC1, Aβ and phosphorylated tau may reduce the abnormal interaction between VDAC1 and APP, VDAC1 and Aβ, and VDAC1 and phosphorylated tau; and that reduced levels of VDAC1, Aβ and phosphorylated tau may maintain normal mitochondrial pore opening and pore closure, ultimately leading to normal mitochondrial function, mitochondria supplying ATP to nerve terminals and boosting synaptic and cognitive function in AD.
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Affiliation(s)
- Maria Manczak
- Neurogenetics Laboratory, Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science University, Beaverton, OR 97006, USA
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8
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Colombini M. VDAC structure, selectivity, and dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1457-65. [PMID: 22240010 DOI: 10.1016/j.bbamem.2011.12.026] [Citation(s) in RCA: 210] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 12/02/2011] [Accepted: 12/22/2011] [Indexed: 11/29/2022]
Abstract
VDAC channels exist in the mitochondrial outer membrane of all eukaryotic organisms. Of the different isoforms present in one organism, it seems that one of these is the canonical VDAC whose properties and 3D structure are highly conserved. The fundamental role of these channels is to control the flux of metabolites between the cytosol and mitochondrial spaces. Based on many functional studies, the fundamental structure of the pore wall consists of one α helix and 13 β strands tilted at a 46° angle. This results in a pore with an estimated internal diameter of 2.5nm. This structure has not yet been resolved. The published 3D structure consists of 19 β strands and is different from the functional structure that forms voltage-gated channels. The selectivity of the channel is exquisite, being able to select for ATP over molecules of the same size and charge. Voltage gating involves two separate gating processes. The mechanism involves the translocation of a positively charged portion of the wall of the channel to the membrane surface resulting in a reduction in pore diameter and volume and an inversion in ion selectivity. This mechanism is consistent with experiments probing changes in selectivity, voltage gating, kinetics and energetics. Other published mechanisms are in conflict with experimental results. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism.
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Affiliation(s)
- Marco Colombini
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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9
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Bay DC, Court DA. Effects of ergosterol on the structure and activity of Neurospora mitochondrial porin in liposomes. Can J Microbiol 2009; 55:1275-83. [DOI: 10.1139/w09-088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondrial porins (also known as voltage-dependent anion-selective channels (VDACs)) regulate and contribute to cellular metabolism. These proteins copurify with sterols, and some purified forms of the protein require sterol for insertion into planar artificial membranes. Recently, interactions between detergent-solubilized mitochondrial porins and sterols have been detected by NMR and spectroscopic methods, but the effects of sterols on pore function remained to be assessed. Therefore, in this work, a freeze–thaw technique was used to introduce recombinant Neurospora porin into liposomes containing, or lacking, the native fungal sterol ergosterol. In both types of liposomes, insertion of the protein converts it to a protease-resistant state and low levels of dimeric and trimeric forms are observed. There are only minor differences between the secondary structural components of the protein in the presence or absence of sterol. Ergosterol in proteoliposomes alters their osmotic responses to sucrose, possibly due to increased membrane rigidity or interactions with the protein that were not revealed by the methods used in this study. The presence of ergosterol is associated with an increased change in conformation and loss of function of liposome-embedded porin at high temperature. Taken with other evidence for direct interactions of sterols with porins, these results support a link between these two molecules in mitochondrial membrane activity.
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Affiliation(s)
- Denice C. Bay
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
| | - Deborah A. Court
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
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10
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Hirano M, Takeuchi Y, Aoki T, Yanagida T, Ide T. Current Recordings of Ion Channel Proteins Immobilized on Resin Beads. Anal Chem 2009; 81:3151-4. [DOI: 10.1021/ac900286z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Minako Hirano
- Network Center for Molecular and System Life Sciences, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka Suita, Osaka 565-0871, Japan
| | - Yuko Takeuchi
- Network Center for Molecular and System Life Sciences, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka Suita, Osaka 565-0871, Japan
| | - Takaaki Aoki
- Network Center for Molecular and System Life Sciences, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka Suita, Osaka 565-0871, Japan
| | - Toshio Yanagida
- Network Center for Molecular and System Life Sciences, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka Suita, Osaka 565-0871, Japan
| | - Toru Ide
- Network Center for Molecular and System Life Sciences, Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka Suita, Osaka 565-0871, Japan
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11
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Roman I, Figys J, Steurs G, Zizi M. Direct measurement of VDAC-actin interaction by surface plasmon resonance. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:479-86. [PMID: 16678788 DOI: 10.1016/j.bbamem.2006.03.019] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 02/20/2006] [Accepted: 03/16/2006] [Indexed: 11/21/2022]
Abstract
VDAC--a mitochondrial channel involved in the control of aerobic metabolism and apoptosis--interacts in vitro and in vivo with a wide repertoire of proteins including cytoskeletal elements. A functional interaction between actin and Neurospora crassa VDAC was reported, excluding other VDAC isoforms. From a recent genome-wide screen of the VDAC interactome, we found that human actin is a putative ligand of yeast VDAC. Since such interaction may have broader implications for various mitochondrial processes, we probed it with Surface Plasmon Resonance (SPR) technology using purified yeast VDAC (YVDAC) and rabbit muscle G-actin (RGA). We show that RGA binds to immobilized YVDAC in a reversible and dose-dependent manner with saturating kinetics and an apparent K(D) of 50 microg/ml (1.2 microM actin). BSA does not bind VDAC regardless of the concentrations. Alternatively, VDAC binds similarly to immobilized RGA but without saturating kinetics. VDAC being known to interact with itself, this latter interaction was directly measured to interpret the RGA signals. VDAC could bind to VDAC without saturating kinetics as expected if higher order binding occurred, and could account for maximally 66% of the non-saturating behavior of VDAC binding onto RGA. Hence, actin-VDAC interactions are not a species-specific oddity and may be a more general phenomenon, the role of which ought to be further investigated.
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Affiliation(s)
- Inge Roman
- Molecular Membrane Biophysics and Neurophysiology, Dept. of Physiology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, 103 Laarbeeklaan, 1090 Brussels, Belgium
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12
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Dai H, Lo YS, Litvinchuk A, Wang YT, Jane WN, Hsiao LJ, Chiang KS. Structural and functional characterizations of mung bean mitochondrial nucleoids. Nucleic Acids Res 2005; 33:4725-39. [PMID: 16116038 PMCID: PMC1188516 DOI: 10.1093/nar/gki783] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mitochondrial nucleoids isolated from mung bean seedlings exhibited a chromatin-like structure associated with a membrane component. A similar structure, which underwent discrete changes during cotyledon development, was identified in situ. Isolated nucleoids consisted of essentially the same phospholipids, including cardiolipin, as whole mitochondria and proteins of inner- and outer-mitochondrial-membrane origin. Actin was consistently found with mitochondrial nucleoids prepared with different detergent concentrations. Formaldehyde cross-linking of cytochalasin B- and proteinase K-treated mitochondria further revealed that actin was associated with DNA in nucleoids. Mitochondrial nucleoids were self-sufficient in directing DNA synthesis in vitro in a pattern mimicking mtDNA synthesis in isolated mitochondria. In pulse-field gel electrophoresis, newly synthesized mtDNA separated into two major components, well-bound and fast-moving forms. Nucleoids DNA synthesis was resistant to aphidicolin but sensitive to N-ethylmaleimide, which indicates that a gamma-type DNA polymerase was responsible for this activity. Mitochondrial nucleoids were capable of self-directed RNA transcription in a non-random fashion in vitro. Consistent with and complementary to results from fungi and human cells done mostly in situ, our present work helps to establish the important paradigm that mitochondrial nucleoids in eukaryotes are more than mere mtDNA compaction and segregation entities but are centers of mtDNA maintenance and expression.
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Affiliation(s)
- Hwa Dai
- Institute of Plant and Microbial Biology, Academia Sinica Taipei, Taiwan 11509, ROC.
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13
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Rostovtseva TK, Antonsson B, Suzuki M, Youle RJ, Colombini M, Bezrukov SM. Bid, but Not Bax, Regulates VDAC Channels. J Biol Chem 2004; 279:13575-83. [PMID: 14729675 DOI: 10.1074/jbc.m310593200] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During apoptosis, cytochrome c is released from mitochondria into the cytosol, where it participates in caspase activation. Various and often conflicting mechanisms have been proposed to account for the increased permeability of the mitochondrial outer membrane that is responsible for this process. The voltage-dependent anion channel (VDAC) is the major permeability pathway for metabolites in the mitochondrial outer membrane and therefore is a very attractive candidate for cytochrome c translocation. Here, we report that properties of VDAC channels reconstituted into planar phospholipid membranes are unaffected by addition of the pro-apoptotic protein Bax under a variety of conditions. Contrary to other reports (Shimizu, S., Narita, M., and Tsujimoto, Y. (1999) Nature 399, 483-487; Shimizu, S., Ide, T., Yanagida, T., and Tsujimoto, Y. (2000) J. Biol. Chem. 275, 12321-12325; Shimizu, S., Konishi, A., Kodama, T., and Tsujimoto, Y. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 3100-3105), we found no electrophysiologically detectable interaction between VDAC channels isolated from mammalian mitochondria and either monomeric or oligomeric forms of Bax. We conclude that Bax does not induce cytochrome c release by acting on VDAC. In contrast to Bax, another pro-apoptotic protein (Bid) proteolytically cleaved with caspase-8 affected the voltage gating of VDAC by inducing channel closure. We speculate that by decreasing the probability of VDAC opening, Bid reduces metabolite exchange between mitochondria and the cytosol, leading to mitochondrial dysfunction.
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Affiliation(s)
- Tatiana K Rostovtseva
- Laboratory of Physical and Structural Biology, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Kleinschmidt JH, Tamm LK. Secondary and tertiary structure formation of the beta-barrel membrane protein OmpA is synchronized and depends on membrane thickness. J Mol Biol 2002; 324:319-30. [PMID: 12441110 DOI: 10.1016/s0022-2836(02)01071-9] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The mechanism of membrane insertion and folding of a beta-barrel membrane protein has been studied using the outer membrane protein A (OmpA) as an example. OmpA forms an eight-stranded beta-barrel that functions as a structural protein and perhaps as an ion channel in the outer membrane of Escherichia coli. OmpA folds spontaneously from a urea-denatured state into lipid bilayers of small unilamellar vesicles. We have used fluorescence spectroscopy, circular dichroism spectroscopy, and gel electrophoresis to investigate basic mechanistic principles of structure formation in OmpA. Folding kinetics followed a second-order rate law and is strongly depended on the hydrophobic thickness of the lipid bilayer. When OmpA was refolded into model membranes of dilaurylphosphatidylcholine, fluorescence kinetics were characterized by a rate constant that was about fivefold higher than the rate constants of formation of secondary and tertiary structure, which were determined by circular dichroism spectroscopy and gel electrophoresis, respectively. The formation of beta-sheet secondary structure and closure of the beta-barrel of OmpA were correlated with the same rate constant and coupled to the insertion of the protein into the lipid bilayer. OmpA, and presumably other beta-barrel membrane proteins therefore do not follow a mechanism according to the two-stage model that has been proposed for the folding of alpha-helical bundle membrane proteins. These different folding mechanisms are likely a consequence of the very different intramolecular hydrogen bonding and hydrophobicity patterns in these two classes of membrane proteins.
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Affiliation(s)
- Jörg H Kleinschmidt
- Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0736, USA
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Li XX, Colombini M. Catalyzed insertion of proteins into phospholipid membranes: specificity of the process. Biophys J 2002; 83:2550-9. [PMID: 12414689 PMCID: PMC1302341 DOI: 10.1016/s0006-3495(02)75266-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The process of insertion of intrinsic proteins into phospholipid membranes conjures up the thought of enormous energy barriers but is a routine occurrence in cells. Proteinaceous complexes responsible for protein targeting/translocation/insertion into membranes have been studied intensively. However, the mitochondrial voltage-dependent anion channel (VDAC), can insert into phospholipid membranes by an auto-catalytic process called "auto-directed insertion." This process results in an oriented insertion of VDAC channels and an increase in insertion rate per unit area of 10 orders of magnitude. Here we report that VDAC catalyzes the insertion of PorA/C1 and KcsA by increasing their calculated insertion rate per unit area by 9 orders of magnitude with no detectable effect on the insertion of alpha-hemolysin. This was measured as a reduction in the delay before the first insertion of these proteins. Gramicidin and PorA/C1 accelerate the calculated insertion rate per unit area of VDAC by 8 and 9 orders of magnitude, respectively. Only PorA/C1 increases the overall rate of VDAC insertion (50-fold) over the self-catalyzed rate. Our results indicate that catalyzed insertion of proteins into phospholipid membranes does not arise simply from disturbance of the phospholipid membrane because it shows strong specificity.
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Affiliation(s)
- Xiao Xian Li
- Department of Biology, University of Maryland, College Park, MD 20742, USA
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16
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Li C, Breton S, Morrison R, Cannon CL, Emma F, Sanchez-Olea R, Bear C, Strange K. Recombinant pICln forms highly cation-selective channels when reconstituted into artificial and biological membranes. J Gen Physiol 1998; 112:727-36. [PMID: 9834142 PMCID: PMC2229450 DOI: 10.1085/jgp.112.6.727] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/1998] [Accepted: 09/21/1998] [Indexed: 11/20/2022] Open
Abstract
pICln has been proposed to be the swelling-activated anion channel responsible for ICl, swell, or a channel regulator. We tested the anion channel hypothesis by reconstituting recombinant pICln into artificial and biological membranes. Single channels were observed when pICln was reconstituted into planar lipid bilayers. In the presence of symmetrical 300 mM KCl, the channels had a high open probability and a slope conductance of 48 pS, and were outwardly rectifying. Reduction of trans KCl to 50 mM shifted the reversal potential by -31.2 +/- 0.06 mV, demonstrating that the channel is at least seven times more selective for cations than for anions. Consistent with this finding, channel conductance was unaffected by substitution of Cl- with glutamate, but was undetectable when K+ was replaced by N-methyl-D-glucamine. Reconstitution of pICln into liposomes increased 86Rb+ uptake by three- to fourfold, but had no effect on 36Cl- uptake. Phosphorylation of pICln with casein kinase II or mutation of G54, G56, and G58 to alanine decreased channel open probability and 86Rb+ uptake. When added to the external medium bathing Sf9 cells, pICln inserted into the plasma membrane and increased cell cation permeability. Taken together, these observations demonstrate that channel activity is due to pICln and not minor contaminant proteins. However, these findings do not support the hypothesis that pICln is the anion-selective ICl, swell channel. The observed cation channel activity may reflect an as yet to be defined physiological function of pICln, or may be a consequence of in vitro reconstitution of purified, recombinant protein.
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Affiliation(s)
- C Li
- Division of Cell Biology, Research Institute, Hospital for Sick Children and Physiology Department, University of Toronto, Toronto, Ontario, Canada M5G 1X8
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17
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Báthori G, Szabó I, Schmehl I, Tombola F, Messina A, De Pinto V, Zoratti M. Novel aspects of the electrophysiology of mitochondrial porin. Biochem Biophys Res Commun 1998; 243:258-63. [PMID: 9473514 DOI: 10.1006/bbrc.1997.7926] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The recent findings that mitochondrial porin, VDAC, participates in supramolecular complexes and is present in the plasmamembrane need to be reconciled with its biophysical properties. We report here that VDAC often displays previously unobserved or unappreciated behaviors. Reconstituted VDAC can: a) exhibit fast gating when in any of many conductance substates; b) close completely, although briefly, on its own; c) close for a long periods, in the presence of König's polyanion; d) take several milliseconds to re-open when an applied transmembrane potential is switched off; e) be desensitized by prolonged exposure to high voltages, so that it will not re-open to the full conductance state upon subsequent return to zero voltage; f) display polarity-dependent voltage-induced closure. These behaviors are especially noticeable when the observations are conducted on a single reincorporated channel, suggesting that interactions between copies of VDAC may play a role in determining its electrophysiological properties. Any model of VDAC's structure, gating and function should take these observations into account.
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Affiliation(s)
- G Báthori
- CNR Unit for Biomembranes, Department of Biomedical Sciences, University of Padova, Italy
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