Voltage-dependent anion channel

Last updated
Eukaryotic porin
Human Voltage-Dependent Anion Channel Protein Structure.png
Crystal Structure of the Human Voltage-Dependent Anion Channel. The arrows denote the antiparallel beta sheets that form the characteristic beta-barrel
Identifiers
SymbolPorin_3
Pfam PF01459
InterPro IPR001925
PROSITE PDOC00483
TCDB 1.B.8
OPM superfamily 189
OPM protein 3emn
CDD cd07306
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

Voltage-dependent anion channels, or mitochondrial porins, are a class of porin ion channel located on the outer mitochondrial membrane. [1] [2] There is debate as to whether or not this channel is expressed in the cell surface membrane. [3] [4] [5]

Contents

This major protein of the outer mitochondrial membrane of eukaryotes forms a voltage-dependent anion-selective channel (VDAC) that behaves as a general diffusion pore for small hydrophilic molecules. [6] [7] [8] [9] The channel adopts an open conformation at low or zero membrane potential and a closed conformation at potentials above 30–40 mV. VDAC facilitates the exchange of ions and molecules between mitochondria and cytosol and is regulated by the interactions with other proteins and small molecules. [10]

Structure

This protein contains about 280 amino acids and forms a beta barrel which spans the mitochondrial outer membrane. [11] [12]

Since its discovery in 1976, extensive function and structure analysis of VDAC proteins has been conducted. A prominent feature of the pore emerged: when reconstituted into planar lipid bilayers, there is a voltage-dependent switch between an anion-selective high-conductance state with high metabolite flux and a cation-selective low-conductance state with limited passage of metabolites.

More than 30 years after its initial discovery, in 2008, three independent structural projects of VDAC-1 were completed. The first was solved by multi-dimensional NMR spectroscopy. The second applied a hybrid approach using crystallographic data. The third was for mouse VDAC-1 crystals determined by X-ray crystallographic techniques. The three projects of the 3D structures of VDAC-1 revealed many structural features. First, VDAC-1 represents a new structural class of outer membrane β-barrel proteins with an odd number of strands. Another aspect is that the negatively charged side chain of residue E73 is oriented towards the hydrophobic membrane environment. The 19-stranded 3D structure obtained under different experimental sources by three different laboratories fits the EM and AFM data from native membrane sources and represents a biologically relevant state of VDAC-1. [10]

Mechanism

At membrane potentials exceeding 30 mV (positive or negative), VDAC assumes a closed state, and transitions to its open state once the voltage drops below this threshold. Although both states allow passage of simple salts, VDAC is much more stringent with organic anions, a category into which most metabolites fall. [13] The precise mechanism for coupling voltage changes to conformational changes within the protein has not yet been worked out, but studies by Thomas et al. suggest that when the protein transitions to the closed form, voltage changes lead to the removal of a large section of the protein from the channel and decrease effective pore radius. [14] Several lysine residues, as well as Glu-152, have been implicated as especially important sensor residues within the protein. [15]

Biological function

The voltage-dependent ion channel plays a key role in regulating metabolic and energetic flux across the outer mitochondrial membrane. It is involved in the transport of ATP, ADP, pyruvate, malate, and other metabolites, and thus communicates extensively with enzymes from metabolic pathways. [13] The ATP-dependent cytosolic enzymes hexokinase, glucokinase, and glycerol kinase, as well as the mitochondrial enzyme creatine kinase, have all been found to bind to VDAC. This binding puts them in close proximity to ATP released from the mitochondria. In particular, the binding of hexokinase is presumed to play a key role in coupling glycolysis to oxidative phosphorylation. [14] Additionally, VDAC is an important regulator of Ca2+ transport in and out of the mitochondria. Because Ca2+ is a cofactor for metabolic enzymes such as pyruvate dehydrogenase and isocitrate dehydrogenase, energetic production and homeostasis are both affected by VDAC's permeability to Ca2+. [16]

Disease relevance

VDAC has also been shown to play a role in apoptosis. [17] During apoptosis, VDAC modifies the mitochondrial permeability transition pore to release of apoptogenic factors such as cytochrome c. However, VDAC are not essential components of the mitochondrial permeability transition pore. Although cytochrome c plays an essential role in oxidative phosphorylation within the mitochondrion. In the cytosol it activates proteolytic enzymes called caspases, which play a major role in cell death. [18] Although the mechanism for VDAC-facilitated cytochrome c release has not yet been fully elucidated, some research suggests that oligomerization between individual subunits may create a large flexible pore through which cytochrome c can pass. [19] A more important factor is that release of cytochrome c is also regulated by the Bcl-2 protein family: Bax interacts directly with VDAC to increase pore size and promote cytochrome c release, while anti-apoptotic Bcl-xL produces the exact opposite effect. [20] In fact, it has been shown that antibodies that inhibit VDAC also interfere with Bax-mediated cytochrome c release in both isolated mitochondria and whole cells. [21] This key role in apoptosis suggests VDAC as a potential target for chemotherapeutic drugs.

Examples

Yeast contains two members of this family (genes POR1 and POR2); vertebrates have at least three members (genes VDAC1, VDAC2 and VDAC3). [11]

Humans, like most higher eukaryotes, encode three different VDACs; VDAC1, VDAC2, and VDAC3. Together with TOMM40 and TOMM40L they represent a family of evolutionarily related β-barrels. [22]

Plants have the largest number of VDACs. Arabidopsis encode four different VDACs but this number can be larger in other species. [23]

Related Research Articles

<span class="mw-page-title-main">Mitochondrion</span> Organelle in eukaryotic cells responsible for respiration

A mitochondrion is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used throughout the cell as a source of chemical energy. They were discovered by Albert von Kölliker in 1857 in the voluntary muscles of insects. The term mitochondrion was coined by Carl Benda in 1898. The mitochondrion is popularly nicknamed the "powerhouse of the cell", a phrase coined by Philip Siekevitz in a 1957 article of the same name.

<span class="mw-page-title-main">Cytochrome c</span> Protein-coding gene in the species Homo sapiens

The cytochrome complex, or cyt c, is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion where it plays a critical role in cellular respiration. It transfers electrons between Complexes III and IV. Cytochrome c is highly water-soluble, unlike other cytochromes. It is capable of undergoing oxidation and reduction as its iron atom converts between the ferrous and ferric forms, but does not bind oxygen. It also plays a major role in cell apoptosis. In humans, cytochrome c is encoded by the CYCS gene.

<span class="mw-page-title-main">Porin (protein)</span> Group of transport proteins

Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules. They are present in the outer membrane of gram-negative bacteria and some gram-positive mycobacteria, the outer membrane of mitochondria, and the outer chloroplast membrane.

<span class="mw-page-title-main">Intermembrane space</span>

The intermembrane space (IMS) is the space occurring between or involving two or more membranes. In cell biology, it is most commonly described as the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. It also refers to the space between the inner and outer nuclear membranes of the nuclear envelope, but is often called the perinuclear space. The IMS of mitochondria plays a crucial role in coordinating a variety of cellular activities, such as regulation of respiration and metabolic functions. Unlike the IMS of the mitochondria, the IMS of the chloroplast does not seem to have any obvious function.

<span class="mw-page-title-main">Inner mitochondrial membrane</span>

The inner mitochondrial membrane (IMM) is the mitochondrial membrane which separates the mitochondrial matrix from the intermembrane space.

The mitochondrial permeability transition pore is a protein that is formed in the inner membrane of the mitochondria under certain pathological conditions such as traumatic brain injury and stroke. Opening allows increase in the permeability of the mitochondrial membranes to molecules of less than 1500 daltons in molecular weight. Induction of the permeability transition pore, mitochondrial membrane permeability transition, can lead to mitochondrial swelling and cell death through apoptosis or necrosis depending on the particular biological setting.

<span class="mw-page-title-main">Phospholipid scramblase</span> Protein

Scramblase is a protein responsible for the translocation of phospholipids between the two monolayers of a lipid bilayer of a cell membrane. In humans, phospholipid scramblases (PLSCRs) constitute a family of five homologous proteins that are named as hPLSCR1–hPLSCR5. Scramblases are members of the general family of transmembrane lipid transporters known as flippases. Scramblases are distinct from flippases and floppases. Scramblases, flippases, and floppases are three different types of enzymatic groups of phospholipid transportation enzymes. The inner-leaflet, facing the inside of the cell, contains negatively charged amino-phospholipids and phosphatidylethanolamine. The outer-leaflet, facing the outside environment, contains phosphatidylcholine and sphingomyelin. Scramblase is an enzyme, present in the cell membrane, that can transport (scramble) the negatively charged phospholipids from the inner-leaflet to the outer-leaflet, and vice versa.

<span class="mw-page-title-main">Apoptosis regulator BAX</span> Mammalian protein found in Homo sapiens

Apoptosis regulator BAX, also known as bcl-2-like protein 4, is a protein that in humans is encoded by the BAX gene. BAX is a member of the Bcl-2 gene family. BCL2 family members form hetero- or homodimers and act as anti- or pro-apoptotic regulators that are involved in a wide variety of cellular activities. This protein forms a heterodimer with BCL2, and functions as an apoptotic activator. This protein is reported to interact with, and increase the opening of, the mitochondrial voltage-dependent anion channel (VDAC), which leads to the loss in membrane potential and the release of cytochrome c. The expression of this gene is regulated by the tumor suppressor P53 and has been shown to be involved in P53-mediated apoptosis.

<span class="mw-page-title-main">BH3 interacting-domain death agonist</span> Protein-coding gene in the species Homo sapiens

The BH3 interacting-domain death agonist, or BID, gene is a pro-apoptotic member of the Bcl-2 protein family. Bcl-2 family members share one or more of the four characteristic domains of homology entitled the Bcl-2 homology (BH) domains, and can form hetero- or homodimers. Bcl-2 proteins act as anti- or pro-apoptotic regulators that are involved in a wide variety of cellular activities.

<span class="mw-page-title-main">Bcl-2 homologous antagonist killer</span> Protein-coding gene in the species Homo sapiens

Bcl-2 homologous antagonist/killer is a protein that in humans is encoded by the BAK1 gene on chromosome 6. The protein encoded by this gene belongs to the BCL2 protein family. BCL2 family members form oligomers or heterodimers and act as anti- or pro-apoptotic regulators that are involved in a wide variety of cellular activities. This protein localizes to mitochondria, and functions to induce apoptosis. It interacts with and accelerates the opening of the mitochondrial voltage-dependent anion channel, which leads to a loss in membrane potential and the release of cytochrome c. This protein also interacts with the tumor suppressor P53 after exposure to cell stress.

<span class="mw-page-title-main">Mitochondrial membrane transport protein</span>

Mitochondrial membrane transport proteins, also known as mitochondrial carrier proteins, are proteins which exist in the membranes of mitochondria. They serve to transport molecules and other factors, such as ions, into or out of the organelles. Mitochondria contain both an inner and outer membrane, separated by the inter-membrane space, or inner boundary membrane. The outer membrane is porous, whereas the inner membrane restricts the movement of all molecules. The two membranes also vary in membrane potential and pH. These factors play a role in the function of mitochondrial membrane transport proteins. There are 53 discovered human mitochondrial membrane transporters, with many others that are known to still need discovered.

<span class="mw-page-title-main">Bcl-2-like protein 1</span> Protein-coding gene in the species Homo sapiens

Bcl-2-like protein 1 is a protein encoded in humans by the BCL2L1 gene. Through alternative splicing, the gene encodes both of the human proteins Bcl-xL and Bcl-xS.

<span class="mw-page-title-main">HK1</span> Mammalian protein found in Homo sapiens

Hexokinase-1 (HK1) is an enzyme that in humans is encoded by the HK1 gene on chromosome 10. Hexokinases phosphorylate glucose to produce glucose-6-phosphate (G6P), the first step in most glucose metabolism pathways. This gene encodes a ubiquitous form of hexokinase which localizes to the outer membrane of mitochondria. Mutations in this gene have been associated with hemolytic anemia due to hexokinase deficiency. Alternative splicing of this gene results in five transcript variants which encode different isoforms, some of which are tissue-specific. Each isoform has a distinct N-terminus; the remainder of the protein is identical among all the isoforms. A sixth transcript variant has been described, but due to the presence of several stop codons, it is not thought to encode a protein. [provided by RefSeq, Apr 2009]

<span class="mw-page-title-main">Mitochondrial apoptosis-induced channel</span>

The mitochondrial apoptosis-induced channel, is an early marker of the onset of apoptosis. This ion channel is formed on the outer mitochondrial membrane in response to certain apoptotic stimuli. MAC activity is detected by patch clamping mitochondria from apoptotic cells at the time of cytochrome c release.

<span class="mw-page-title-main">VDAC1</span> Protein-coding gene in the species Homo sapiens

Voltage-dependent anion-selective channel 1 (VDAC-1) is a beta barrel protein that in humans is encoded by the VDAC1 gene located on chromosome 5. It forms an ion channel in the outer mitochondrial membrane (OMM) and also the outer cell membrane. In the OMM, it allows ATP to diffuse out of the mitochondria into the cytoplasm. In the cell membrane, it is involved in volume regulation. Within all eukaryotic cells, mitochondria are responsible for synthesis of ATP among other metabolite needed for cell survival. VDAC1 therefore allows for communication between the mitochondrion and the cell mediating the balance between cell metabolism and cell death. Besides metabolic permeation, VDAC1 also acts as a scaffold for proteins such as hexokinase that can in turn regulate metabolism.

<span class="mw-page-title-main">VDAC2</span> Protein-coding gene in the species Homo sapiens

Voltage-dependent anion-selective channel protein 2 is a protein that in humans is encoded by the VDAC2 gene on chromosome 10. This protein is a voltage-dependent anion channel and shares high structural homology with the other VDAC isoforms. VDACs are generally involved in the regulation of cell metabolism, mitochondrial apoptosis, and spermatogenesis. Additionally, VDAC2 participates in cardiac contractions and pulmonary circulation, which implicate it in cardiopulmonary diseases. VDAC2 also mediates immune response to infectious bursal disease (IBD).

<span class="mw-page-title-main">VDAC3</span> Protein-coding gene in the species Homo sapiens

Voltage-dependent anion-selective channel protein 3 (VDAC3) is a protein that in humans is encoded by the VDAC3 gene on chromosome 8. The protein encoded by this gene is a voltage-dependent anion channel and shares high structural homology with the other VDAC isoforms. Nonetheless, VDAC3 demonstrates limited pore-forming ability and, instead, interacts with other proteins to perform its biological functions, including sperm flagella assembly and centriole assembly. Mutations in VDAC3 have been linked to male infertility, as well as Parkinson’s disease.

<span class="mw-page-title-main">Bcl-2 family</span>

The Bcl-2 family consists of a number of evolutionarily-conserved proteins that share Bcl-2 homology (BH) domains. The Bcl-2 family is most notable for their regulation of apoptosis, a form of programmed cell death, at the mitochondrion. The Bcl-2 family proteins consists of members that either promote or inhibit apoptosis, and control apoptosis by governing mitochondrial outer membrane permeabilization (MOMP), which is a key step in the intrinsic pathway of apoptosis. A total of 25 genes in the Bcl-2 family were identified by 2008.

Tryptophan-rich sensory proteins (TspO) are a family of proteins that are involved in transmembrane signalling. In either prokaryotes or mitochondria they are localized to the outer membrane, and have been shown to bind and transport dicarboxylic tetrapyrrole intermediates of the haem biosynthetic pathway. They are associated with the major outer membrane porins and with the voltage-dependent anion channel.

<span class="mw-page-title-main">Mitochondria associated membranes</span> Cellular structure

Mitochondria-associated membranes (MAM) represent a region of the endoplasmic reticulum (ER) which is reversibly tethered to mitochondria. These membranes are involved in import of certain lipids from the ER to mitochondria and in regulation of calcium homeostasis, mitochondrial function, autophagy and apoptosis. They also play a role in development of neurodegenerative diseases and glucose homeostasis.

References

  1. ↑ Hoogenboom BW, Suda K, Engel A, Fotiadis D (2007). "The supramolecular assemblies of voltage-dependent anion channels in the native membrane". J. Mol. Biol. 370 (2): 246–55. doi:10.1016/j.jmb.2007.04.073. PMID   17524423.
  2. ↑ Blachly-Dyson, E; Forte, M (September 2001). "VDAC channels". IUBMB Life. 52 (3–5): 113–8. doi: 10.1080/15216540152845902 . PMID   11798022. S2CID   38314888.
  3. ↑ Sabirov RZ, Merzlyak PG (June 2012). "Plasmalemmal VDAC controversies and maxi-anion channel puzzle". Biochim. Biophys. Acta. 1818 (6): 1570–80. doi: 10.1016/j.bbamem.2011.09.024 . PMID   21986486.
  4. ↑ De Pinto, V.; Messina, A.; Lane, D. J. R.; Lawen, A. (2010). "Voltage-dependent anion-selective channel (VDAC) in the plasma membrane". FEBS Letters. 584 (9): 1793–1799. doi: 10.1016/j.febslet.2010.02.049 . PMID   20184885. S2CID   3391282.
  5. ↑ Niehage, C.; Steenblock, C.; Pursche, T.; Bornhäuser, M.; Corbeil, D.; Hoflack, B. (2011). Borlongan, Cesario V (ed.). "The Cell Surface Proteome of Human Mesenchymal Stromal Cells". PLOS ONE. 6 (5): e20399. Bibcode:2011PLoSO...620399N. doi: 10.1371/journal.pone.0020399 . PMC   3102717 . PMID   21637820.
  6. ↑ Benz R (1994). "Permeation of hydrophilic solutes through mitochondrial outer membranes: review on mitochondrial porins". Biochim. Biophys. Acta. 1197 (2): 167–196. doi:10.1016/0304-4157(94)90004-3. PMID   8031826.
  7. ↑ Mannella CA (1992). "The 'ins' and 'outs' of mitochondrial membrane channels". Trends Biochem. Sci. 17 (8): 315–320. doi:10.1016/0968-0004(92)90444-E. PMID   1384178.
  8. ↑ Dihanich M (1990). "The biogenesis and function of eukaryotic porins". Experientia. 46 (2): 146–153. doi:10.1007/BF02027310. PMID   1689252. S2CID   2199583.
  9. ↑ Forte M, Guy HR, Mannella CA (1987). "Molecular genetics of the VDAC ion channel: structural model and sequence analysis". J. Bioenerg. Biomembr. 19 (4): 341–350. doi:10.1007/BF00768537. PMID   2442148. S2CID   10219032.
  10. 1 2 Hiller S, Abramson J, Mannella C, Wagner G, Zeth K (September 2010). "The 3D structures of VDAC represent a native conformation". Trends Biochem. Sci. 35 (9): 514–21. doi:10.1016/j.tibs.2010.03.005. PMC   2933295 . PMID   20708406.
  11. 1 2 Sampson MJ, Lovell RS, Davison DB, Craigen WJ (1996). "A novel mouse mitochondrial voltage-dependent anion channel gene localizes to chromosome 8". Genomics. 36 (1): 192–196. doi:10.1006/geno.1996.0445. PMID   8812436.
  12. ↑ Zeth K (2010). "Structure and evolution of mitochondrial outer membrane proteins of beta-barrel topology". Biochim. Biophys. Acta. 1797 (6–7): 1292–9. doi: 10.1016/j.bbabio.2010.04.019 . PMID   20450883.
  13. 1 2 Blachly-Dyson, E. & Forte, M. (2001). "VDAC Channels". IUBMB Life. 52 (3–5): 113–18. doi: 10.1080/15216540152845902 . PMID   11798022. S2CID   38314888.
  14. 1 2 Colombini M, Blachly-Dyson E, Forte M (1996). "VDAC, a Channel in the Outer Mitochondrial Membrane". Ion Channels. Vol. 4. pp. 169–202. doi:10.1007/978-1-4899-1775-1_5. ISBN   978-1-4899-1777-5. PMID   8744209.
  15. ↑ Thomas L, Blachly-Dyson E, Colombini M, Forte M (June 1993). "Mapping of residues forming the voltage sensor of the voltage-dependent anion-selective channel". Proc. Natl. Acad. Sci. U.S.A. 90 (12): 5446–9. Bibcode:1993PNAS...90.5446T. doi: 10.1073/pnas.90.12.5446 . PMC   46737 . PMID   7685903.
  16. ↑ Shoshan-Barmatz V; Gincel D. (2003). "The voltage-dependent anion channel: characterization, modulation, and role in mitochondrial function in cell life and death". Cell Biochem. Biophys. 39 (3): 279–92. doi:10.1385/CBB:39:3:279. PMID   14716081. S2CID   33628015.
  17. ↑ Lemasters JJ; Holmuhamedov E. (2006). "Voltage-dependent anion channel (VDAC) as mitochondrial governator--thinking outside the box". Biochim. Biophys. Acta. 1762 (2): 181–90. doi: 10.1016/j.bbadis.2005.10.006 . PMID   16307870.
  18. ↑ Tsujimoto Y, Shimizu S (2002). "The voltage-dependent anion channel: an essential player in apoptosis". Biochimie. 84 (2–3): 187–93. doi:10.1016/S0300-9084(02)01370-6. PMID   12022949.
  19. ↑ Zalk R; Israelson A; Garty ES; Azoulay-Zohar H; Shoshan-Barmatz V. (2005). "Oligomeric states of the voltage-dependent anion channel and cytochrome c release from mitochondria". Biochem. J. 386 (1): 73–83. doi:10.1042/BJ20041356. PMC   1134768 . PMID   15456403.
  20. ↑ Shimizu S; Narita M; Tsujimoto Y. (1999). "Bcl-2 family proteins regulate the release of apoptogenic cytochrome c by the mitochondrial channel VDAC". Nature. 399 (6735): 483–7. Bibcode:1999Natur.399..483S. doi:10.1038/20959. PMID   10365962. S2CID   4423304.
  21. ↑ Shimizu S; Matsuoka Y; Shinohara Y; Yoneda Y; Tsujimoto Y. (2001). "Essential role of voltage-dependent anion channel in various forms of apoptosis in mammalian cells". J. Cell Biol. 152 (2): 237–50. doi:10.1083/jcb.152.2.237. PMC   2199613 . PMID   11266442.
  22. ↑ Bay DC, Hafez M, Young MJ, Court DA (June 2012). "Phylogenetic and coevolutionary analysis of the β-barrel protein family comprised of mitochondrial porin (VDAC) and Tom40". Biochim. Biophys. Acta. 1818 (6): 1502–19. doi: 10.1016/j.bbamem.2011.11.027 . PMID   22178864.
  23. ↑ Homblé F, Krammer E, Prevost M (June 2012). "Plant VDAC: facts and speculations". Biochim. Biophys. Acta. 1818 (6): 1486–501. doi: 10.1016/j.bbamem.2011.11.028 . PMID   22155681.
This article incorporates text from the public domain Pfam and InterPro: IPR001925
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.