1
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Benz R. Historical Perspective of Pore-Forming Activity Studies of Voltage-Dependent Anion Channel (Eukaryotic or Mitochondrial Porin) Since Its Discovery in the 70th of the Last Century. Front Physiol 2021; 12:734226. [PMID: 35547863 PMCID: PMC9083909 DOI: 10.3389/fphys.2021.734226] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 09/24/2021] [Indexed: 01/07/2023] Open
Abstract
Eukaryotic porin, also known as Voltage-Dependent Anion Channel (VDAC), is the most frequent protein in the outer membrane of mitochondria that are responsible for cellular respiration. Mitochondria are most likely descendants of strictly aerobic Gram-negative bacteria from the α-proteobacterial lineage. In accordance with the presumed ancestor, mitochondria are surrounded by two membranes. The mitochondrial outer membrane contains besides the eukaryotic porins responsible for its major permeability properties a variety of other not fully identified channels. It encloses also the TOM apparatus together with the sorting mechanism SAM, responsible for the uptake and assembly of many mitochondrial proteins that are encoded in the nucleus and synthesized in the cytoplasm at free ribosomes. The recognition and the study of electrophysiological properties of eukaryotic porin or VDAC started in the late seventies of the last century by a study of Schein et al., who reconstituted the pore from crude extracts of Paramecium mitochondria into planar lipid bilayer membranes. Whereas the literature about structure and function of eukaryotic porins was comparatively rare during the first 10years after the first study, the number of publications started to explode with the first sequencing of human Porin 31HL and the recognition of the important function of eukaryotic porins in mitochondrial metabolism. Many genomes contain more than one gene coding for homologs of eukaryotic porins. More than 100 sequences of eukaryotic porins are known to date. Although the sequence identity between them is relatively low, the polypeptide length and in particular, the electrophysiological characteristics are highly preserved. This means that all eukaryotic porins studied to date are anion selective in the open state. They are voltage-dependent and switch into cation-selective substates at voltages in the physiological relevant range. A major breakthrough was also the elucidation of the 3D structure of the eukaryotic pore, which is formed by 19 β-strands similar to those of bacterial porin channels. The function of the presumed gate an α-helical stretch of 20 amino acids allowed further studies with respect to voltage dependence and function, but its exact role in channel gating is still not fully understood.
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2
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Di Rosa MC, Guarino F, Conti Nibali S, Magrì A, De Pinto V. Voltage-Dependent Anion Selective Channel Isoforms in Yeast: Expression, Structure, and Functions. Front Physiol 2021; 12:675708. [PMID: 34093236 PMCID: PMC8171188 DOI: 10.3389/fphys.2021.675708] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Accepted: 04/20/2021] [Indexed: 12/25/2022] Open
Abstract
Mitochondrial porins, also known as voltage-dependent anion selective channels (VDACs), are pore-forming molecules of the outer mitochondrial membranes, involved in the regulation of metabolic flux between cytosol and mitochondria. Playing such an essential role, VDAC proteins are evolutionary conserved and isoforms are present in numerous species. The quest for specific function(s) related to the raise of multiple isoforms is an intriguing theme. The yeast Saccharomyces cerevisiae genome is endowed with two different VDAC genes encoding for two distinct porin isoforms, definitely less characterized in comparison to mammalian counterpart. While yVDAC1 has been extensively studied, the second isoform, yVDAC2, is much less expressed, and has a still misunderstood function. This review will recapitulate the known and poorly known information in the literature, in the light of the growing interest about the features of VDAC isoforms in the cell.
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Affiliation(s)
- Maria Carmela Di Rosa
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Francesca Guarino
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy.,we.MitoBiotech S.R.L., Catania, Italy
| | - Stefano Conti Nibali
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
| | - Andrea Magrì
- we.MitoBiotech S.R.L., Catania, Italy.,Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy
| | - Vito De Pinto
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy.,we.MitoBiotech S.R.L., Catania, Italy
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3
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Alpha-Synuclein and Mitochondrial Dysfunction in Parkinson's Disease: The Emerging Role of VDAC. Biomolecules 2021; 11:biom11050718. [PMID: 34064816 PMCID: PMC8170894 DOI: 10.3390/biom11050718] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 05/05/2021] [Accepted: 05/08/2021] [Indexed: 12/12/2022] Open
Abstract
Alpha-Synuclein (αSyn) is a protein whose function is still debated, as well as its role in modulation of mitochondrial function in both physiological and pathological conditions. Mitochondrial porins or Voltage-Dependent Anion Channel (VDAC) proteins are the main gates for ADP/ATP and various substrates towards the organelle. Furthermore, they act as a mitochondrial hub for many cytosolic proteins, including αSyn. This review analyzes the main aspects of αSyn-mitochondria interaction, focusing on the role of VDAC and its emerging involvement in the pathological processes.
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4
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De Pinto V. Renaissance of VDAC: New Insights on a Protein Family at the Interface between Mitochondria and Cytosol. Biomolecules 2021; 11:biom11010107. [PMID: 33467485 PMCID: PMC7831034 DOI: 10.3390/biom11010107] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/10/2021] [Accepted: 01/12/2021] [Indexed: 12/14/2022] Open
Abstract
It has become impossible to review all the existing literature on Voltage-Dependent Anion selective Channel (VDAC) in a single article. A real Renaissance of studies brings this protein to the center of decisive knowledge both for cell physiology and therapeutic application. This review, after highlighting the similarities between the cellular context and the study methods of the solute carriers present in the inner membrane and VDAC in the outer membrane of the mitochondria, will focus on the isoforms of VDAC and their biochemical characteristics. In particular, the possible reasons for their evolutionary onset will be discussed. The variations in their post-translational modifications and the differences between the regulatory regions of their genes, probably the key to understanding the current presence of these genes, will be described. Finally, the situation in the higher eukaryotes will be compared to that of yeast, a unicellular eukaryote, where there is only one active isoform and the role of VDAC in energy metabolism is better understood.
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Affiliation(s)
- Vito De Pinto
- Department of Biomedicine and Biotechnology Sciences, University of Catania, Via S. Sofia 64, 95123 Catania, Italy; ; Tel.: +39-095-73842444
- we.MitoBiotech.srl, c.so Italia 172, 95129 Catania, Italy
- National Institute of Biostructures and Biosystems, Section of Catania, 00136 Rome, Italy
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5
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Magrì A, Karachitos A, Di Rosa MC, Reina S, Conti Nibali S, Messina A, Kmita H, De Pinto V. Recombinant yeast VDAC2: a comparison of electrophysiological features with the native form. FEBS Open Bio 2019; 9:1184-1193. [PMID: 31206247 PMCID: PMC6609568 DOI: 10.1002/2211-5463.12574] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 12/04/2018] [Accepted: 12/10/2018] [Indexed: 12/22/2022] Open
Abstract
Voltage‐dependent anion channel isoform 2 of the yeast Saccharomyces cerevisiae (yVDAC2) was believed for many years to be devoid of channel activity. Recently, we isolated yVDAC2 and showed that it exhibits channel‐forming activity in the planar lipid bilayer system when in its so‐called native form. Here, we describe an alternative strategy for yVDAC2 isolation, through heterologous expression in bacteria and refolding in vitro. Recombinant yVDAC2, like its native form, is able to form voltage‐dependent channels. However, some differences between native and recombinant yVDAC2 emerged in terms of voltage dependence and ion selectivity, suggesting that, in this specific case, the recombinant protein might be depleted of post‐translational modification(s) that occur in eukaryotic cells.
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Affiliation(s)
- Andrea Magrì
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy.,Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy
| | - Andonis Karachitos
- Department of Bioenergetics, Faculty of Biology, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Poznan, Poland
| | - Maria Carmela Di Rosa
- Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy
| | - Simona Reina
- Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy
| | - Stefano Conti Nibali
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy
| | - Angela Messina
- Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy.,National Institute for Biomembranes and Biosystems, Section of Catania, Italy
| | - Hanna Kmita
- Department of Bioenergetics, Faculty of Biology, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Poznan, Poland
| | - Vito De Pinto
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy.,National Institute for Biomembranes and Biosystems, Section of Catania, Italy
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6
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Magrì A, Reina S, De Pinto V. VDAC1 as Pharmacological Target in Cancer and Neurodegeneration: Focus on Its Role in Apoptosis. Front Chem 2018; 6:108. [PMID: 29682501 PMCID: PMC5897536 DOI: 10.3389/fchem.2018.00108] [Citation(s) in RCA: 108] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 03/22/2018] [Indexed: 01/15/2023] Open
Abstract
Cancer and neurodegeneration are different classes of diseases that share the involvement of mitochondria in their pathogenesis. Whereas the high glycolytic rate (the so-called Warburg metabolism) and the suppression of apoptosis are key elements for the establishment and maintenance of cancer cells, mitochondrial dysfunction and increased cell death mark neurodegeneration. As a main actor in the regulation of cell metabolism and apoptosis, VDAC may represent the common point between these two broad families of pathologies. Located in the outer mitochondrial membrane, VDAC forms channels that control the flux of ions and metabolites across the mitochondrion thus mediating the organelle's cross-talk with the rest of the cell. Furthermore, the interaction with both pro-apoptotic and anti-apoptotic factors makes VDAC a gatekeeper for mitochondria-mediated cell death and survival signaling pathways. Unfortunately, the lack of an evident druggability of this protein, since it has no defined binding or active sites, makes the quest for VDAC interacting molecules a difficult tale. Pharmacologically active molecules of different classes have been proposed to hit cancer and neurodegeneration. In this work, we provide an exhaustive and detailed survey of all the molecules, peptides, and microRNAs that exploit VDAC in the treatment of the two examined classes of pathologies. The mechanism of action and the potential or effectiveness of each compound are discussed.
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Affiliation(s)
- Andrea Magrì
- Section of Molecular Biology, Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy.,Section of Biology and Genetics, Department of Biomedicine and Biotechnology, National Institute for Biomembranes and Biosystems, Section of Catania, Catania, Italy
| | - Simona Reina
- Section of Molecular Biology, Department of Biological, Geological and Environmental Sciences, University of Catania, Catania, Italy.,Section of Biology and Genetics, Department of Biomedicine and Biotechnology, National Institute for Biomembranes and Biosystems, Section of Catania, Catania, Italy
| | - Vito De Pinto
- Section of Biology and Genetics, Department of Biomedicine and Biotechnology, National Institute for Biomembranes and Biosystems, Section of Catania, Catania, Italy
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7
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Leggio L, Guarino F, Magrì A, Accardi-Gheit R, Reina S, Specchia V, Damiano F, Tomasello MF, Tommasino M, Messina A. Mechanism of translation control of the alternative Drosophila melanogaster Voltage Dependent Anion-selective Channel 1 mRNAs. Sci Rep 2018; 8:5347. [PMID: 29593233 PMCID: PMC5871876 DOI: 10.1038/s41598-018-23730-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 03/19/2018] [Indexed: 01/08/2023] Open
Abstract
The eukaryotic porin, also called the Voltage Dependent Anion-selective Channel (VDAC), is the main pore-forming protein of the outer mitochondrial membrane. In Drosophila melanogaster, a cluster of genes evolutionarily linked to VDAC is present on chromosome 2L. The main VDAC isoform, called VDAC1 (Porin1), is expressed from the first gene of the cluster. The porin1 gene produces two splice variants, 1A-VDAC and 1B-VDAC, with the same coding sequence but different 5' untranslated regions (UTRs). Here, we studied the influence of the two 5' UTRs, 1A-5' UTR and 1B-5' UTR, on transcription and translation of VDAC1 mRNAs. In porin-less yeast cells, transformation with a construct carrying 1A-VDAC results in the expression of the corresponding protein and in complementation of a defective cell phenotype, whereas the 1B-VDAC sequence actively represses VDAC expression. Identical results were obtained using constructs containing the two 5' UTRs upstream of the GFP reporter. A short region of 15 nucleotides in the 1B-5' UTR should be able to pair with an exposed helix of 18S ribosomal RNA (rRNA), and this interaction could be involved in the translational repression. Our data suggest that contacts between the 5' UTR and 18S rRNA sequences could modulate the translation of Drosophila 1B-VDAC mRNA. The evolutionary significance of this finding is discussed.
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Affiliation(s)
- L Leggio
- Department of Biological, University of Catania, Geological and Environmental Sciences, Catania, 95125, Italy.,Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, 95123, Italy
| | - F Guarino
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, 95123, Italy.,National Institute of Biostructures and Biosystems (INBB), Catania, Italy
| | - A Magrì
- Department of Biological, University of Catania, Geological and Environmental Sciences, Catania, 95125, Italy
| | - R Accardi-Gheit
- International Agency for Research on Cancer (IARC), World Health Organization, Lyon, 69372, France
| | - S Reina
- Department of Biological, University of Catania, Geological and Environmental Sciences, Catania, 95125, Italy.,Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, 95123, Italy
| | - V Specchia
- Department of Biological and Environmental Sciences and Technologies (DiSTeBA), University of Salento, Lecce, Italy
| | - F Damiano
- Department of Biological and Environmental Sciences and Technologies (DiSTeBA), University of Salento, Lecce, Italy
| | - M F Tomasello
- IBB-CNR, Institute of Biostructure and Bioimaging, Section of Catania, Via Paolo Gaifami, 18-95126, Catania, Italy
| | - M Tommasino
- International Agency for Research on Cancer (IARC), World Health Organization, Lyon, 69372, France
| | - A Messina
- Department of Biological, University of Catania, Geological and Environmental Sciences, Catania, 95125, Italy. .,National Institute of Biostructures and Biosystems (INBB), Catania, Italy.
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8
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Guardiani C, Magrì A, Karachitos A, Di Rosa MC, Reina S, Bodrenko I, Messina A, Kmita H, Ceccarelli M, De Pinto V. yVDAC2, the second mitochondrial porin isoform of Saccharomyces cerevisiae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:270-279. [PMID: 29408701 DOI: 10.1016/j.bbabio.2018.01.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Revised: 01/09/2018] [Accepted: 01/25/2018] [Indexed: 10/18/2022]
Abstract
The yeast Saccharomyces cerevisiae genome is endowed with two distinct isoforms of Voltage-Dependent Anion Channel (VDAC). The isoform yVDAC2 is currently understudied with respect to the best known yVDAC1. Yet, since the discovery, the function of yVDAC2 was unclear, leading to the hypothesis that it might be devoid of a channel function. In this work we have elucidated, by bioinformatics modeling and electrophysiological analysis, the functional activity of yVDAC2. The conformation of yVDAC2 and, for comparison, of yVDAC1 were modeled using a multiple template approach involving mouse, human and zebrafish structures and both showed to arrange the sequences as the typical 19-stranded VDAC β-barrel. Molecular dynamics simulations showed that yVDAC2, in comparison with yVDAC1, has a different number of permeation paths of potassium and chloride ions. yVDAC2 protein was over-expressed in the S. cerevisiae cells depleted of functional yVDAC1 (Δpor1 mutant) and, after purification, it was reconstituted in artificial membranes (planar lipid bilayer (PLB) system). The protein displayed channel-forming activity and the calculated conductance, voltage-dependence and ion selectivity values were similar to those of yVDAC1 and other members of VDAC family. This is the first time that yVDAC2 channel features are detected and characterized.
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Affiliation(s)
| | - Andrea Magrì
- Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy
| | - Andonis Karachitos
- Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland
| | - Maria Carmela Di Rosa
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy
| | - Simona Reina
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy
| | - Igor Bodrenko
- Department of Physics, University of Cagliari, Cagliari, Italy
| | - Angela Messina
- Department of Biological, Geological and Environmental Sciences, Section of Molecular Biology, University of Catania, Italy
| | - Hanna Kmita
- Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Poznan, Poland.
| | | | - Vito De Pinto
- Department of Biomedical and Biotechnological Sciences, University of Catania, Italy.
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9
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Danelishvili L, Chinison JJJ, Pham T, Gupta R, Bermudez LE. The Voltage-Dependent Anion Channels (VDAC) of Mycobacterium avium phagosome are associated with bacterial survival and lipid export in macrophages. Sci Rep 2017; 7:7007. [PMID: 28765557 PMCID: PMC5539096 DOI: 10.1038/s41598-017-06700-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 06/16/2017] [Indexed: 01/02/2023] Open
Abstract
Mycobacterium avium subsp. hominissuis is associated with infection of immunocompromised individuals as well as patients with chronic lung disease. M. avium infects macrophages and actively interfere with the host killing machinery such as apoptosis and autophagy. Bacteria alter the normal endosomal trafficking, prevent the maturation of phagosomes and modify many signaling pathways inside of the macrophage by secreting effector molecules into the cytoplasm. To investigate whether M. avium needs to attach to the internal surface of the vacuole membrane before releasing efferent molecules, vacuole membrane proteins were purified and binding to the surface molecules present in intracellular bacteria was evaluated. The voltage-dependent anion channels (VDAC) were identified as components of M. avium vacuoles in macrophages. M. avium mmpL4 proteins were found to bind to VDAC-1 protein. The inactivation of VDAC-1 function either by pharmacological means or siRNA lead to significant decrease of M. avium survival. Although, we could not establish a role of VDAC channels in the transport of known secreted M. avium proteins, we demonstrated that the porin channels are associated with the export of bacterial cell wall lipids outside of vacuole. Suppression of the host phagosomal transport systems and the pathogen transporter may serve as therapeutic targets for infectious diseases.
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Affiliation(s)
- Lia Danelishvili
- Department of Biomedical Sciences, College of Veterinary Medicine, Corvallis, OR, USA.
| | - Jessica J J Chinison
- Department of Biomedical Sciences, College of Veterinary Medicine, Corvallis, OR, USA.,Department of Microbiology, College of Science, Corvallis, OR, USA
| | - Tuan Pham
- Department of Biochemistry and Biophysics, College of Science, Oregon State University, Corvallis, Oregon, 97331, USA
| | - Rashmi Gupta
- Department of Biomedical Sciences, College of Veterinary Medicine, Corvallis, OR, USA.,College of Medicine, University of Central Florida, Orlando, Florida, 32827, USA
| | - Luiz E Bermudez
- Department of Biomedical Sciences, College of Veterinary Medicine, Corvallis, OR, USA. .,Department of Microbiology, College of Science, Corvallis, OR, USA.
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10
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Saletti R, Reina S, Pittalà MG, Belfiore R, Cunsolo V, Messina A, De Pinto V, Foti S. High resolution mass spectrometry characterization of the oxidation pattern of methionine and cysteine residues in rat liver mitochondria voltage-dependent anion selective channel 3 (VDAC3). BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:301-311. [DOI: 10.1016/j.bbamem.2016.12.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 11/18/2016] [Accepted: 12/14/2016] [Indexed: 10/20/2022]
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11
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Reina S, Guarino F, Magrì A, De Pinto V. VDAC3 As a Potential Marker of Mitochondrial Status Is Involved in Cancer and Pathology. Front Oncol 2016; 6:264. [PMID: 28066720 PMCID: PMC5179545 DOI: 10.3389/fonc.2016.00264] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 12/09/2016] [Indexed: 01/24/2023] Open
Abstract
VDAC3 is the least known isoform of the mammalian voltage-dependent anion selective channels of the outer mitochondrial membrane. It has been recently shown that cysteine residues of VDAC3 are found over-oxidized. The VDAC3 cysteine over-oxidation was associated with the oxidizing environment and the abundance of reactive oxygen species (ROS) in the intermembrane space. In this work, we have examined the role of VDAC3 in general pathogenic mechanisms at the basis of mitochondrial dysfunction and involving the mitochondrial quality control. Many of the diseases reported here, including cancer and viral infections, are often associated with significant changes in the intracellular redox state. In this sense, VDAC3 bearing oxidative modifications could become marker of the oxidative load in the mitochondria and part of the ROS signaling pathway.
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Affiliation(s)
- Simona Reina
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy; National Institute of Biostructures and Biosystems (INBB), Rome, Italy
| | - Francesca Guarino
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy; National Institute of Biostructures and Biosystems (INBB), Rome, Italy
| | - Andrea Magrì
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy; National Institute of Biostructures and Biosystems (INBB), Rome, Italy
| | - Vito De Pinto
- Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy; National Institute of Biostructures and Biosystems (INBB), Rome, Italy
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12
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VDAC, a multi-functional mitochondrial protein regulating cell life and death. Mol Aspects Med 2010; 31:227-85. [PMID: 20346371 DOI: 10.1016/j.mam.2010.03.002] [Citation(s) in RCA: 530] [Impact Index Per Article: 37.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 03/17/2010] [Indexed: 01/22/2023]
Abstract
Research over the past decade has extended the prevailing view of the mitochondrion to include functions well beyond the generation of cellular energy. It is now recognized that mitochondria play a crucial role in cell signaling events, inter-organellar communication, aging, cell proliferation, diseases and cell death. Thus, mitochondria play a central role in the regulation of apoptosis (programmed cell death) and serve as the venue for cellular decisions leading to cell life or death. One of the mitochondrial proteins controlling cell life and death is the voltage-dependent anion channel (VDAC), also known as mitochondrial porin. VDAC, located in the mitochondrial outer membrane, functions as gatekeeper for the entry and exit of mitochondrial metabolites, thereby controlling cross-talk between mitochondria and the rest of the cell. VDAC is also a key player in mitochondria-mediated apoptosis. Thus, in addition to regulating the metabolic and energetic functions of mitochondria, VDAC appears to be a convergence point for a variety of cell survival and cell death signals mediated by its association with various ligands and proteins. In this article, we review what is known about the VDAC channel in terms of its structure, relevance to ATP rationing, Ca(2+) homeostasis, protection against oxidative stress, regulation of apoptosis, involvement in several diseases and its role in the action of different drugs. In light of our recent findings and the recently solved NMR- and crystallography-based 3D structures of VDAC1, the focus of this review will be on the central role of VDAC in cell life and death, addressing VDAC function in the regulation of mitochondria-mediated apoptosis with an emphasis on structure-function relations. Understanding structure-function relationships of VDAC is critical for deciphering how this channel can perform such a variety of functions, all important for cell life and death. This review also provides insight into the potential of VDAC1 as a rational target for new therapeutics.
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13
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De Pinto V, Messina A, Lane DJ, Lawen A. Voltage-dependent anion-selective channel (VDAC) in the plasma membrane. FEBS Lett 2010; 584:1793-9. [DOI: 10.1016/j.febslet.2010.02.049] [Citation(s) in RCA: 122] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 02/15/2010] [Accepted: 02/16/2010] [Indexed: 10/19/2022]
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14
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Abstract
A variety of ion channels, including members of all major ion channel families, have been shown to be regulated by changes in the level of membrane cholesterol and partition into cholesterol-rich membrane domains. In general, several types of cholesterol effects have been described. The most common effect is suppression of channel activity by an increase in membrane cholesterol, an effect that was described for several types of inwardly-rectifying K(+) channels, voltage-gated K(+) channels, Ca(+2) sensitive K(+) channels, voltage-gated Na(+) channels, N-type voltage-gated Ca(+2) channels and volume-regulated anion channels. In contrast, several types of ion channels, such as epithelial amiloride-sensitive Na(+) channels and Transient Receptor Potential channels, as well as some of the types of inwardly-rectifying and voltage-gated K(+) channels were shown to be inhibited by cholesterol depletion. Cholesterol was also shown to alter the kinetic properties and current-voltage dependence of several voltage-gated channels. Finally, maintaining membrane cholesterol level is required for coupling ion channels to signalling cascades. In terms of the mechanisms, three general mechanisms have been proposed: (i) specific interactions between cholesterol and the channel protein, (ii) changes in the physical properties of the membrane bilayer and (iii) maintaining the scaffolds for protein-protein interactions. The goal of this review is to describe systematically the role of cholesterol in regulation of the major types of ion channels and to discuss these effects in the context of the models proposed.
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Affiliation(s)
- Irena Levitan
- Department of Medicine, University of Illinois at Chicago, Chicago, IL, USA.
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15
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De Pinto V, Messina A, Schmid A, Simonetti S, Carnevale F, Benz R. Characterization of channel-forming activity in muscle biopsy from a porin-deficient human patient. J Bioenerg Biomembr 2009; 32:585-93. [PMID: 15254372 DOI: 10.1023/a:1005622611410] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A bioptic specimen from the muscles of a patient suffering from severe myopathy was inspected for the presence of human porin 31HL. Western blotting suggested that the specimen was free of the most abundant eukaryotic porin 31HL (HVDAC1). The specimen was treated with detergent and the soluble protein fraction was passed through a dry hydroxyapatite column. The passthrough of this column was inspected for channel formation in artificial lipid-bilayer membranes. The channel observed under these conditions had a single-channel conductance of about 2.5 nS in 1 M KCl, was cation selective, and was found to be virtually voltage independent. Experiments with a control specimen from a healthy human being, without any indication for muscle myopathy, revealed the presence of the voltage-dependent porin 31HL in the sample. It is discussed whether the patient's bioptic specimen contained another human porin, which has not been studied to date in its natural environment.
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Affiliation(s)
- V De Pinto
- Department of Chemical Sciences, Laboratory of Biochemistry and Molecular Biology, Università di Catania, viale A. Doria 6, I-95125 Catania, Italy.
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16
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Porin isoform 2 has a different localization in Drosophila melanogaster ovaries than porin 1. J Bioenerg Biomembr 2008; 40:219-26. [DOI: 10.1007/s10863-008-9149-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Accepted: 05/22/2008] [Indexed: 11/25/2022]
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17
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Lee S, Leung HT, Kim E, Jang J, Lee E, Baek K, Pak WL, Yoon J. Effects of a mutation in the Drosophila porin gene encoding mitochondrial voltage-dependent anion channel protein on phototransduction. Dev Neurobiol 2007; 67:1533-45. [PMID: 17525991 DOI: 10.1002/dneu.20526] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Mitochondrial porins, also know as VDACs (voltage-dependent anion channels), play an important role in regulating energy metabolism, apoptosis, and the transport of metabolites across the mitochondrial outer membrane. So far three distinct isoforms of VDAC (VDAC1-3) have been reported in vertebrates, but their functions remain unknown. The annotation database of the Drosophila melanogaster genome sequence has identified four genes (porin, CG17137, CG17139, and CG17140) encoding different isoforms of VDACs. We identified post-translational modifications of PORIN that are specific to D. melanogaster eyes. We also identified the P-element insertion in the porin gene, porin(G2294), that is homozygous viable whereas all the porin mutants previously reported are homozygous lethal at the pupal stage. The mutant does not show any defects in fly morphology, survival, and photoreceptor structure. The mutant, however, produces <10% of the normal level of wild-type (WT) porin transcripts and 16.5% of WT level of the PORIN protein. The P-element insertion affects only the expression of Class I transcript but not Class II transcript of the porin gene. Unlike in WT, the mutant displays an ERG (electroretinogram) that is not maintained during a prolonged light stimulus. The revertant obtained from remobilization of the P-element in the mutant produces the WT level of porin transcripts and PORIN protein, and shows a normal ERG response. Our data suggest that the PORIN protein is important in maintaining a photoreceptor response during prolonged stimulation.
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Affiliation(s)
- Sunji Lee
- Graduate School of Biotechnology, KyungHee University, Yongin-si, Gyeonggi-do, Korea
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18
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Komarov AG, Graham BH, Craigen WJ, Colombini M. The physiological properties of a novel family of VDAC-like proteins from Drosophila melanogaster. Biophys J 2004; 86:152-62. [PMID: 14695259 PMCID: PMC1303779 DOI: 10.1016/s0006-3495(04)74093-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
VDAC, a major protein of the mitochondrial outer membrane, forms voltage-dependent, anion-selective channels permeable to most metabolites. Although multiple isoforms of VDAC have been found in different organisms, only one isoform (porin/DVDAC) has been previously reported for Drosophila melanogaster. We have examined the physiological properties of three other Drosophila proteins (CG17137, CG17139, and CG17140) whose primary sequences have significant homology to DVDAC. A comparison of their hydropathy profiles (beta-pattern) with known VDAC sequences indicates the same fundamental folding pattern but with major insertions and deletions. The ability of these proteins to form channels was tested on planar membranes and liposomes. Channel activity was observed with varying degrees of similarity to VDAC. Two of these proteins (CG17137 and CG17140) produced channels with anionic selectivity in the open state. Sometimes channels exhibited closure and voltage gating, but for CG17140 this occurred at much higher voltages than is typical for VDAC. CG17139 was not able to form channels. DVDAC and CG17137 were able to rescue the temperature-sensitive conditional-lethal phenotype of VDAC-deficient yeast, whereas CG17139 and CG17140 demonstrated no complementation. Similar structure and channel formation indicate that VDAC-like proteins are part of the larger VDAC family but the modifications are indicative of specialized functions.
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Affiliation(s)
- Alexander G Komarov
- Department of Biology, University of Maryland, College Park, Maryland 20742, USA
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19
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Aiello R, Messina A, Schiffler B, Benz R, Tasco G, Casadio R, De Pinto V. Functional Characterization of a Second Porin Isoform in Drosophila melanogaster. J Biol Chem 2004; 279:25364-73. [PMID: 15054101 DOI: 10.1074/jbc.m310572200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial porins or voltage-dependent anion-selective channels are channel-forming proteins mainly found in the mitochondrial outer membrane. Genome sequencing of the fruit fly Drosophila melanogaster revealed the presence of three additional porin-like genes. No functional information was available for the different gene products. In this work we have studied the function of the gene product closest to the known Porin gene (CG17137 coding for DmPorin2). Its coding sequence was expressed in Escherichia coli. The recombinant DmPorin2 protein is able to form channels similar to those formed by DmPorin1 reconstituted in artificial membranes. Furthermore, DmPorin2 is clearly voltage-independent and cation-selective, whereas its counterpart isoform 1 is voltage-dependent and anion-selective. Sequence comparison of the two porin isoforms indicates the exchange of four lysines in DmPorin1 for four glutamic acids in DmPorin2. We have mutated two of them (Glu-66 and Glu-163) to lysines to investigate their role in the functional features of the pore. The mutants E163K and E66K/E163K are endowed with an almost full inversion of the ion selectivity. Both single mutations partially restore the voltage dependence of the pore. We found that an additional effect with the double mutant E66K/E163K was the restoration of voltage dependence. Protein structure predictions highlight a 16 beta-strand pattern, typical for porins. In a three-dimensional model of DmPorin2, Glu-66 and Glu-163 are close to the rim of the channel, on two opposite sides. DmPorin2 is expressed in all the fly tissues and in all the developmental stages tested. Our main conclusions are as follows. 1) The CG17137 gene may express a porin with a functional role in D. melanogaster. 2) We have identified two amino acids of major relevance for the voltage dependence of the porin pore.
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Affiliation(s)
- Rita Aiello
- Department of Chemical Sciences, University of Catania, 95125 Catania, Italy
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20
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Laver DR, Peter WG. Interpretation of substates in ion channels: unipores or multipores? PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 67:99-140. [PMID: 9446932 DOI: 10.1016/s0079-6107(97)00008-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- D R Laver
- John Curtin School of Medical Research, Australian National University, Camberra, ACT, Australia
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21
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Ryerse J, Colombini M, Hagerty T, Nagel B, Liu TT. Isolation and characterization of the mitochondrial channel, VDAC, from the insect Heliothis virescens. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1327:193-203. [PMID: 9271261 DOI: 10.1016/s0005-2736(97)00058-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A 31 kDa voltage-dependent anion-selective channel (VDAC) protein was purified from the insect Heliothis virescens (tobacco budworm, denoted TBW) using an alkali extraction and filtration procedure and was characterized by SDS-PAGE, amino acid sequencing, biophysical properties and immunocytochemistry. The N-terminal sequence has highest identity with VDACs from mammals (50-66%) followed by plants (34-41%) and lower eukaryotes (30-34%). Reconstitution in planar phospholipid membranes yielded properties typical of VDACs from other organisms including a single-channel conductance of 4.1 nS (in 1 M KCl), closure in response to positive and negative transmembrane voltage, and a reversal potential of 11.8 mV indicating anion selectivity in the open state. A polyclonal antiserum (R19) raised against gel-purified 31 kDa protein specifically labelled mitochondria and mitochondrial outer membranes in TBW flight muscle by light and electron microscope immunocytochemistry.
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Affiliation(s)
- J Ryerse
- Department of Pathology, St. Louis University Health Sciences Center, MO 63104, USA.
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22
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Ryerse J, Blachly-Dyson E, Forte M, Nagel B. Cloning and molecular characterization of a voltage-dependent anion-selective channel (VDAC) from Drosophila melanogaster. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1327:204-12. [PMID: 9271262 DOI: 10.1016/s0005-2736(97)00059-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A full length voltage-dependent anion-selective channel (VDAC) cDNA was cloned from Drosophila melanogaster by expression library screening using an antibody against an insect VDAC protein. The cDNA clone (denoted DmVDAC) is 1082 base pairs (bp) in length and contains an open reading frame (bp 62-907) encoding a 282 amino acid protein which has a predicted molecular mass of 30550 Da, a predicted pI of 6.98 and no cysteines. Hydrophobicity analysis suggests 15 or 16 membrane-spanning domains. The DmVDAC amino acid sequence has variable homology with VDACs from other species ranging from 62% identity with a human VDAC to 23% identity with a Dictyostelium discoideum VDAC. DmVDAC has 92% identity with the 38 conserved residues in a VDAC consensus sequence. DmVDAC was expressed in VDAC-null yeast but failed to rescue viability. DmVDAC has 88% identity at the amino acid level and 99% identity at the nucleic acid level with a recently reported D. melanogaster VDAC sequence (A. Messina et al., FEBS Lett. 384 (1996) 9-13). Homology analyses with the Messina and other VDAC sequences indicate that the amino acid differences are due to minor errors in the Messina sequence. Southern blots and chromosomal in situ hybridizations suggest a single VDAC gene occurs in the fly with a locus at 32B on the left arm of the second chromosome.
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Affiliation(s)
- J Ryerse
- Department of Pathology, St. Louis University Health Sciences Center, MO 63104, USA.
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23
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Wiesner P, Popp B, Schmid A, Benz R, Kayser H. Isolation of mitochondrial porin of the fly Protophormia: porin modification by the pesticide CGA 140'408 studied in lipid bilayer membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1282:216-24. [PMID: 8703976 DOI: 10.1016/0005-2736(96)00059-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Mitochondrial porin from the fly Protophormia was solubilized with detergent from whole mitochondria and purified by chromatography across a hydroxyapatite (HPT) column. The purified protein had an apparent molecular mass of about 30 kDa on SDS-PAGE. Partial sequencing of the protein confirmed that it is porin. When reconstituted in planar lipid bilayer membranes, porin formed ion-permeable channels with single-channel conductances of 2.4 and 4.5 nS in 1 M KCl. At low voltage, Protophormia porin displayed the properties of a general diffusion pore and had a small selectivity for anions over cations. At transmembrane potentials starting with about 20-30 mV, the channel switched in closed state, which is still ion-permeable. Our results suggest that Protophormia porin possesses functional properties similar to those of other mitochondrial porins. Porin was also isolated and purified from mitochondria, which were treated with the carbodiimide CGA 140'408 It represents the active derivative of diafenthiuron a new acaricide and insecticide. This carbodiimide labels both a F0-component of the inner membrane ATPase and outer membrane porin in a similar way as N,N'-dicyclohexylcarbodiimide (DCCD). Reconstitution experiments with the CGA 140'408-modified porin showed no significant effect of the modification on the single-channel conductance, suggesting that CGA 140'408 binds outside the channel. The voltage-dependence of the CGA 140'408-modified porin was changed with respect to the unmodified form. The closed configuration of the pesticide-modified channel was reached at smaller transmembrane potentials, suggesting a shift of the open to the closed state of Protophormia porin by pesticide binding. A possible contribution of this effect to the pesticide action is discussed.
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Affiliation(s)
- P Wiesner
- Lehrstuhl für Biotechnologie, Theodor-Boveri-Institut (Biozentrum), Universität Würzburg, Germany
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24
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Messina A, Neri M, Perosa F, Caggese C, Marino M, Caizzi R, De Pinto V. Cloning and chromosomal localization of a cDNA encoding a mitochondrial porin from Drosophila melanogaster. FEBS Lett 1996; 384:9-13. [PMID: 8797793 DOI: 10.1016/0014-5793(96)00268-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have raised polyclonal antibodies against purified the Drosphila melanogaster mitochondrial porin. They showed high titre and specificity and were thus used as a tool for screening an expression library. The isolated clone 1T1 showed 74% sequence identity in the last 19 residues at the C-terminus of human porin. A subclone of 1T1, containing the porin-like sequence, was thus used as a probe for re-screening a cDNA library and several positive clones were plaque-purified. We present here the sequence of a 1363 bp cDNA encoding a protein of 279 amino acids. Its identity with porin was also confirmed by N-terminal Edman degradation of the purified protein. The D. melanogaster porin shows an overall 51.8% identity with human porin isoform 1 (porin 31HL or HVDAC1) and an overall 55.7% identity with human porin isoform 2 (HVDAC2). Hydrophobicity plots and secondary structure predictions showed a very high similarity with data obtained from known porin sequences. The D. melanogaster porin cDNA was used as a probe for in situ hybridization to polytenic salivar gland chromosomes. It hybridizes with different intensities in two sites, in chromosome 2L, at region 31E and in chromosome 3L at region 79D. Thus, also in Drosophila melanogaster porin polypeptide(s) belong(s) to a multigene family.
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Affiliation(s)
- A Messina
- Istituto di Scienze Biochimiche e Farmacologiche, Facoltà di Scienze M.F.N., Università di Catania, Italy
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25
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Abstract
Higher eukaryotes, including mammals and plants, express a family of VDAC proteins each encoded by a distinct gene. Two human genes encoding VDAC isoforms (HVDAC1 and HVDAC2) have been characterized in greatest detail. These genes generate three proteins that differ primarily by the addition of distinct N terminal extensions in HVDAC2 and HVDAC2', a splice variant of HVDAC2, relative to HVDAC1. Since N terminal sequences have been demonstrated to target many proteins to appropriate subcellular compartments, this observation raises the possibility that the N terminal differences found in HVDAC isoforms may lead to targeting of each protein to different cellular locations. Consistent with this hypothesis, a large number of reports have provided evidence consistent with the notion that HVDAC1 and its homolog in related mammalian species may specifically be present in the plasma membrane or other nonmitochondrial cellular compartments. Here, we review this information and conclude that if VDAC molecules are present at nonmitochondrial locations in mammalian cells, these are unlikely to be the known products of the HVDAC1 or HVDAC2 genes.
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Affiliation(s)
- W H Yu
- Department of Cell and Developmental Biology, Oregon Health Sciences University, Portland 97201, USA
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26
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Lewis TM, Roberts ML, Bretag AH. Immunolabelling for VDAC, the mitochondrial voltage-dependent anion channel, on sarcoplasmic reticulum from amphibian skeletal muscle. Neurosci Lett 1994; 181:83-6. [PMID: 7898777 DOI: 10.1016/0304-3940(94)90565-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Patch-clamp studies of ion channels in the sarcoball membrane, a relatively pure preparation of sarcoplasmic reticulum, had earlier revealed a high-conductance anion channel with some properties similar to the mitochondrial voltage-dependent anion channel (VDAC). Using post-embedding immunolabelling, the presence of VDAC was investigated in sarcoball preparations from the semitendinosus muscle of the cane toad Bufo marinus. As expected, the outer membrane of mitochondria found within the interior of skinned fibres was decorated with gold label. Surprisingly, sarcoplasmic reticulum membrane was also labelled. The sarcoball membranes, which could arise from either the sarcoplasmic reticulum or from mitochondria, were also labelled. These results indicate the presence of a VDAC-like protein in the sarcoplasmic reticulum.
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Affiliation(s)
- T M Lewis
- Department of Physiology, University of Adelaide, Australia
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27
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Benz R. Permeation of hydrophilic solutes through mitochondrial outer membranes: review on mitochondrial porins. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1197:167-96. [PMID: 8031826 DOI: 10.1016/0304-4157(94)90004-3] [Citation(s) in RCA: 347] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- R Benz
- Lehrstuhl für Biotechnologie, Theodor-Boveri-Institut (Biozentrum) der Universität Würzburg, Germany
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28
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Sorgato MC, Moran O. Channels in mitochondrial membranes: knowns, unknowns, and prospects for the future. Crit Rev Biochem Mol Biol 1993; 28:127-71. [PMID: 7683593 DOI: 10.3109/10409239309086793] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Rapid diffusion of hydrophilic molecules across the outer membrane of mitochondria has been related to the presence of a protein of 29 to 37 kDa, called voltage-dependent anion channel (VDAC), able to generate large aqueous pores when integrated in planar lipid bilayers. Functional properties of VDAC from different origins appear highly conserved in artificial membranes: at low transmembrane potentials, the channel is in a highly conducting state, but a raise of the potential (both positive and negative) reduces drastically the current and changes the ionic selectivity from slightly anionic to cationic. It has thus been suggested that VDAC is not a mere molecular sieve but that it may control mitochondrial physiology by restricting the access of metabolites of different valence in response to voltage and/or by interacting with a soluble protein of the intermembrane space. The latest application of the patch clamp and tip-dip techniques, however, has indicated both a different electric behavior of the outer membrane and that other proteins may play a role in the permeation of molecules. Biochemical studies, use of site-directed mutants, and electron microscopy of two-dimensional crystal arrays of VDAC have contributed to propose a monomeric beta barrel as the structural model of the channel. An important insight into the physiology of the inner membrane of mammalian mitochondria has come from the direct observation of the membrane with the patch clamp. A slightly anionic, voltage-dependent conductance of 107 pS and one of 9.7 pS, K(+)-selective and ATP-sensitive, are the best characterized at the single channel level. Under certain conditions, however, the inner membrane can also show unselective nS peak transitions, possibly arising from a cooperative assembly of multiple substrates.
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Affiliation(s)
- M C Sorgato
- Dipartimento di Chimica Biologica, Università di Padova, Italy
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29
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Kalinowski S, Figaszewski Z. A new system for bilayer lipid membrane capacitance measurements: method, apparatus and applications. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1112:57-66. [PMID: 1420270 DOI: 10.1016/0005-2736(92)90254-j] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A new method and a new apparatus for capacitance measurements on bilayer lipid membranes are described. The membrane is charged and discharged with a constant current during the measurement. The charge-discharge cycle duration, which is proportional to the membrane capacitance, is measured. The measured time period is converted into a binary number by digital systems and then this number is either further converted into a constant capacity-proportional voltage or read out by the computer. The apparatus makes it possible to measure the capacitances of voltage-polarized membranes. Application of the apparatus to capacitance measurements of bilayer lipid membranes during their potential on the capacitance is presented. The capacitances of membranes stimulated by rectangular voltage pulses and of those stimulated by a linearly varying potential were reported.
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Affiliation(s)
- S Kalinowski
- Institute of Chemistry, University of Warsaw, Białystok, Poland
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30
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De Pinto VD, Palmieri F. Transmembrane arrangement of mitochondrial porin or voltage-dependent anion channel (VDAC). J Bioenerg Biomembr 1992; 24:21-6. [PMID: 1380500 DOI: 10.1007/bf00769526] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Porin or voltage-dependent anion-selective channel (VDAC) is the main protein responsible for the high permeability of the outer mitochondrial membrane. The mitochondrial porin is mainly composed of sided beta-strands, in analogy with bacterial porin, whose structure has been resolved at 1.8 A resolution. In mitochondrial porins the N-terminal region forms an amphipathic alpha-helix, a structure conserved in organisms very distant from the evolutionary point of view. This part of the protein is exposed to the water phase, as demonstrated by ELISA assays. Various extramembranous loops have been identified by specific proteolytic cleavages. These overall, combined results were used to draw a model of the transmembrane arrangement of mammalian porin. This model is compared to other mitochondrial and bacterial porin models.
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Affiliation(s)
- V D De Pinto
- Department of Pharmaco-Biology, University of Bari, Italy
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31
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De Pinto V, al Jamal JA, Benz R, Genchi G, Palmieri F. Characterization of SH groups in porin of bovine heart mitochondria. Porin cysteines are localized in the channel walls. EUROPEAN JOURNAL OF BIOCHEMISTRY 1991; 202:903-11. [PMID: 1722458 DOI: 10.1111/j.1432-1033.1991.tb16450.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Porin from bovine heart mitochondria contains probably two cysteines (Cys126 and Cys230 in human porin, Kayser, H., Kratzin, H. D., Thinnes, F. P., Götz, H., Schmidt, W. E., Eckart, K. & Hilschmann, N. (1989) Biol. Chem. Hoppe-Seyler 370, 1265-1278). Reduced and oxidized forms of these cysteines were investigated in purified protein and in intact mitochondria using the agents dithioerythritol, cuprous(II) phenantroline, diamide and performic acid. Furthermore, intact mitochondria were labelled with the sulfhydryl-alkylating agents N-[14C]ethylmaleimide, eosin-5-maleimide and N-(1-pyrenyl)-maleimide. Affinity chromatography of bovine heart porin was performed with cysteine-specific material. The results can be summarized as follows: (1) Porin has one reduced and two oxidized forms of apparent molecular masses between 30 and 35 kDa. The native form of porin is the reduced 33 kDa form. The oxidized forms only appear after denaturation with SDS. (2) The 35-kDa reduced and the 33.5-kDa oxidized forms of porin show the same pore-forming properties after reconstitution of the protein into lipid bilayer membranes. (3) Labelling of cysteines by eosin-5-maleimide and N-(1-pyrenyl)-maleimide suggested their location at a boundary between the water-phase and the lipid-phase. Incubation of intact mitochondria with N-ethylmaleimide prior to eosin-5-maleimide and N-(1-pyrenyl)maleimide treatment resulted in the inhibition of the fluorescent labelling. Among the cysteines present in the primary structure, Cys126 is the most sensitive to N-ethylmaleimide binding. (4) Bovine heart mitochondrial porin covalently bound to Affi-Gel 501 (with a 1.75 nm long spacer), but not to Thiopropyl-Sepharose 6B (with a 0.51 nm spacer). This suggests that at least one of the cysteines is localized between 0.51 nm and 1.75 nm deep in the protein micelle.
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Affiliation(s)
- V De Pinto
- Department of Pharmaco-Biology, University of Bari, Italia
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32
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De Pinto V, Prezioso G, Thinnes F, Link TA, Palmieri F. Peptide-specific antibodies and proteases as probes of the transmembrane topology of the bovine heart mitochondrial porin. Biochemistry 1991; 30:10191-200. [PMID: 1718414 DOI: 10.1021/bi00106a017] [Citation(s) in RCA: 113] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have investigated the transmembrane topology of the bovine heart mitochondrial porin by means of proteases and antibodies raised against the amino-terminal region of the protein. The antisera against the human N-terminus reacted with porin in Western blots of NaDodSO4-solubilized bovine heart mitochondria and with the membrane-bound porin in enzyme-linked immunosorbent assay (ELISA). The immunoreaction with mitochondria coated on microtiter wells showed that the amino-terminal region of the protein is not embedded in the lipid bilayer but is exposed to the cytosol. Back-titration of unreacted anti-N-terminal antibodies after their incubation with intact mitochondria demonstrated that the porin N-terminus is also exposed in "noncoated" mitochondria. No difference in antisera reactivity was observed between intact and broken mitochondria. Intact and broken mitochondria were subjected to proteolysis by specific proteases. The membrane-bound bovine heart porin was strongly resistant to proteolysis, but a few specific cleavage sites were observed. Staphylococcus aureus V8 protease gave a large 24K N-terminal peptide, trypsin produced a 12K N-terminal and an 18K C-terminal peptide, and chymotrypsin gave two peptides of Mr 19.5K and 12.5K, which were both recognized by the antiserum against the human N-terminus. Carboxypeptidase A was ineffective in cleaving the membrane-bound porin in both intact and broken mitochondria. Thus, the carboxy-terminal part of the protein is probably not exposed to the water phase. The cleavage patterns of membrane-bound porin, obtained with S. aureus V8 protease, trypsin, and chymotrypsin, showed no difference between intact and broken mitochondria, thus indicating that all porin molecules have the same orientation in the membrane. The computer analysis of the sequence of human B-lymphocyte porin suggested that 16 beta-strands can span the phospholipid bilayer. This result, together with the overall information presented, allowed us to draw a possible scheme of the transmembrane arrangement of mammalian mitochondrial porin.
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Affiliation(s)
- V De Pinto
- Department of Pharmaco-Biology, University of Bari, Germany
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33
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De Pinto V, Zara V, Benz R, Gnoni GV, Palmieri F. Characterization of pore-forming activity in liver mitochondria from Anguilla anguilla. Two porins in mitochondria? BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1061:279-86. [PMID: 1705440 DOI: 10.1016/0005-2736(91)90293-h] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A fast purification procedure for the isolation and purification of eukaryotic porin (De Pinto et al., (1987) Biochim. Biophys. Acta 905, 499-502) was applied to liver mitochondria of the fish Anguilla anguilla. A protein preparation was obtained which formed slightly anionically selective pores in reconstitution experiments with lipid bilayer membranes. The distribution of single-channel conductances had two maxima of 2.4 nS and 4.0 nS in 1 M KCl. Sodium dodecylsulfate electrophoretograms of the protein preparation showed the presence of two bands of very similar electrophoretic mobility (32 and 32.5 kDa). Both bands cross-reacted with antibodies raised against purified bovine heart porin and with antibodies raised against the 19 amino acids N-terminal end of human porin. No cross-reactivity was observed with antibodies against yeast porin. The peptide maps of the two bands showed slight differences. The possibility of the presence of two different porins in liver mitochondria of Anguilla anguilla is discussed. An extensive immunological comparison of different mitochondrial porins is presented.
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Affiliation(s)
- V De Pinto
- Dipartimento Farmaco-Biologico, Università di Bari, Italy
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34
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Abstract
The distribution of gap junction (GJ) protein in Drosophila tissues and developmental stages was determined by probing immuno-blots with an anti-Drosophila GJ protein antibody (R2AP18). All tissues and developmental stages examined contained 18, 24 or 72 kD GJ protein. GJ protein was notably abundant in immuno-blots of homogenates of adult brain tissue. This was confirmed by the direct visualization of GJs in thin sections of adult brain by electron microscopy. GJs were particularly large and numerous between glial cells in the optic lobes and peripheral glial sheath. R2AP18 reactivity was used to identify GJ protein in immunoblots of cell fractions from isolated adult heads. The final GJ-enriched pellets, derived by extracting crude membrane fractions with urea and N-lauroyl sarcosine, contained GJs with reduced profile widths (13-15 nm vs 16-18 nm for native GJs) and which, unlike native GJs in the crude membrane fractions, were immuno-labelled by R2AP18. Immuno-blots of the urea-sarcosine extracted GJ pellets and supernatant contained higher molecular weight R2AP18 immuno-reactive proteins in addition to the 18 kD form which was present in the tissue homogenate and crude membrane fractions. The results confirm previous observations that urea-sarcosine causes alterations in GJ structure and suggest that urea-sarcosine treatment exposes antigenic determinant(s) which are unavailable for R2AP18 binding in non-extracted native GJs. The abundance of GJs in the adult brain and the relatively simple R2AP18 staining patterns in immuno-blots of GJ-enriched fractions from isolated adult heads suggest that this tissue will be useful for further biochemical and molecular studies of GJs in Drosophila.
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Affiliation(s)
- J S Ryerse
- Department of Pathology, St. Louis University School of Medicine, Missouri 63104
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