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Malik C, Ghosh S. Regulation of Single-Channel Conductance of Voltage-Dependent Anion Channel by Mercuric Chloride in a Planar Lipid Bilayer. J Membr Biol 2020; 253:357-371. [PMID: 32748041 DOI: 10.1007/s00232-020-00134-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 07/24/2020] [Indexed: 11/26/2022]
Abstract
The existence of mercury in various forms, e.g., elemental, organic, and inorganic has been known for decades. In any of these forms, it is poisonous to metabolism. In this, an investigation about the effect of the inorganic form of mercury, i.e., mercuric chloride (HgCl2) to the mitochondrial voltage-dependent anion channel (VDAC), has been done after isolation from the cardiac and brain tissues of Wistar rats. In vitro electrophysiology experiments were performed in Cardiolipin planar lipid bilayer membrane (BLM) to study the change in the conductance, selectivity, and gating charge of VDAC post HgCl2 treatment. A reduction in mean conductance of VDAC from 4.3 ± 0.18 to 1.66 ± 0.11 nS was observed. Further, the Gating charge calculated before (± 3.5) and after HgCl2 treatment (± 2.3) showed significant difference. Later, VDAC's behavior was studied at different concentrations of HgCl2 ranging from 0.1 μM to 1 mM. The Inhibitory concentration (IC50) was calculated from the linear regression plot. The IC50 was found to be 488.1 μM. In the asymmetrical HgCl2 (5:1), a permeability ratio of cation to anion was found to be 4.2. It is interpreted that VDAC functioning is affected due to the application of 4 mM HgCl2 and a reduction in the conductance, gating charge, and permeability of VDAC was detected. The results provide clues to HgCl2-induced toxicity mediated through VDAC in the Cardiolipin BLM.
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Affiliation(s)
- Chetan Malik
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India
| | - Subhendu Ghosh
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
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2
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Malty RH, Jessulat M, Jin K, Musso G, Vlasblom J, Phanse S, Zhang Z, Babu M. Mitochondrial targets for pharmacological intervention in human disease. J Proteome Res 2014; 14:5-21. [PMID: 25367773 PMCID: PMC4286170 DOI: 10.1021/pr500813f] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
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Over the past several years, mitochondrial
dysfunction has been
linked to an increasing number of human illnesses, making mitochondrial
proteins (MPs) an ever more appealing target for therapeutic intervention.
With 20% of the mitochondrial proteome (312 of an estimated 1500 MPs)
having known interactions with small molecules, MPs appear to be highly
targetable. Yet, despite these targeted proteins functioning in a
range of biological processes (including induction of apoptosis, calcium
homeostasis, and metabolism), very few of the compounds targeting
MPs find clinical use. Recent work has greatly expanded the number
of proteins known to localize to the mitochondria and has generated
a considerable increase in MP 3D structures available in public databases,
allowing experimental screening and in silico prediction of mitochondrial
drug targets on an unprecedented scale. Here, we summarize the current
literature on clinically active drugs that target MPs, with a focus
on how existing drug targets are distributed across biochemical pathways
and organelle substructures. Also, we examine current strategies for
mitochondrial drug discovery, focusing on genetic, proteomic, and
chemogenomic assays, and relevant model systems. As cell models and
screening techniques improve, MPs appear poised to emerge as relevant
targets for a wide range of complex human diseases, an eventuality
that can be expedited through systematic analysis of MP function.
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Affiliation(s)
- Ramy H Malty
- Department of Biochemistry, Research and Innovation Centre, University of Regina , Regina, Saskatchewan S4S 0A2, Canada
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3
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Dobrov A, Arion VB, Kandler N, Ginzinger W, Jakupec MA, Rufińska A, Graf von Keyserlingk N, Galanski MS, Kowol C, Keppler BK. The First Metal-Based Paullone Derivative with High Antiproliferative Activity in Vitro. Inorg Chem 2006; 45:1945-50. [PMID: 16499355 DOI: 10.1021/ic0511120] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
9-Bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6(5H)-one, kenpaullone, which displays similarities in the activity profile to flavopiridol, was modified by chemical transformations at the lactam unit to provide a peripheral binding site able to accommodate metal ions. The first metal-based paullone has been prepared and characterized by single-crystal X-ray diffraction methods, solid-state cross-polarization magic angle spinning 13C NMR spectroscopy, electrospray ionization mass spectra, and electronic spectra. The gallium complex [GaL2]Cl.2.5H2O, the metal-free ligand (HL), and the starting compound used for the preparation of HL were assessed in vitro for their cytotoxicity in a panel of human tumor cell lines. The gallium complex was found to be 1.5-18-fold more cytotoxic than HL, with an average IC50 value of 2.0 microM.
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Affiliation(s)
- Anatoly Dobrov
- Institute of Inorganic Chemistry, University of Vienna, Waehringerstrasse 42, A-1090 Vienna, Austria
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4
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Abstract
Research on VDAC has accelerated as evidence grows of its importance in mitochondrial function and in apoptosis. New investigators entering the field are often confounded by the VDAC literature and its many apparent conflicts and contradictions. This review is an effort to shed light on the situation and identify reliable information from more questionable claims. Our views on the most important controversial issues are as follows: VDAC is only present in the mitochondrial outer membrane. VDAC functions as a monomer. VDAC functions normally with or without Ca(2+). It does not form channels that mediate the flux of proteins through membranes (peptides and unfolded proteins are excluded from this statement). Closure of VDAC, not VDAC opening, leads to mitochondria outer membrane permeabilization and apoptosis.
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Affiliation(s)
- Tatiana K Rostovtseva
- Laboratory of Physical and Structural Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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5
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Abstract
The mitochondrial outer membrane is not just a barrier but a site of regulation of mitochondrial function. The VDAC family of proteins are the major pathways for metabolite flux through the outer membrane. These can be regulated in a variety of ways and the integration of these regulatory inputs allows mitochondrial metabolism to be adjusted to changing cellular conditions. This includes total blockage of the flux of anionic metabolites leading to permeabilization of the outer membrane to small proteins followed by apoptotic cell death.
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Affiliation(s)
- Marco Colombini
- Department of Biology, University of Maryland, College Park, MD 20742, USA.
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6
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Abstract
Aluminum has been implicated in several neurodegenerative conditions including Alzheimer's disease. Because the mammalian olfactory system has an unusual capacity for the uptake and transneuronal spread of inhaled substances such as aluminum, whole cell recording techniques were used to examine the actions of aluminum on basic membrane properties and amino acid receptors on rat olfactory bulb mitral/tufted (M/T) neurons in culture. Aluminum had little direct effects on M/T neurons. Aluminum (100 microM) did not evoke a membrane current or alter action-potential shape or duration. Aluminum also had no marked effects on the family of voltage-gated membrane currents evoked by a series of 10-mV, 50-ms depolarizing steps. However, aluminum dramatically potentiated the current evoked by 30 microM gamma-aminobutyric acid (GABA) at concentrations <100 microM. Conversely, higher concentrations of aluminum blocked the GABA-evoked current. The effects of aluminum on GABA-evoked currents were not voltage dependent. Aluminum (100 microM) equally potentiated both inward currents at -30 mV and outward currents at + 30 mV. At 300 microM, aluminum blocked both inward and outward currents to a similar extent. In some neurons, aluminum only blocked the current and potentiation was not observed. The biphasic action of aluminum on GABA-evoked currents suggests separate binding sites: a high-affinity potentiating site and a low-affinity inhibiting site. Despite its effects on GABA-evoked currents, aluminum did not alter membrane currents evoked by glutamate, N-methyl-D-aspartate, kainate, or glycine. Aluminum also did not reduce spontaneous excitatory synaptic activity, suggesting little, if any, effect on glutamate release. Although a causal role for aluminum in Alzheimer's disease and other neuropathological conditions remains controversial, it is clear that elevated aluminum concentrations in the brain are associated with a variety of cognitive impairments. The present results indicate that aluminum can alter the function of GABAA receptors and may suggest that aluminum can contribute to cognitive impairment through disruption of inhibitory circuits.
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Affiliation(s)
- P Q Trombley
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4340, USA
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7
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Ahmadzadeh M, Horng A, Colombini M. The control of mitochondrial respiration in yeast: a possible role of the outer mitochondrial membrane. Cell Biochem Funct 1996; 14:201-8. [PMID: 8888574 DOI: 10.1002/cbf.673] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Mitochondrial respiration in yeast (S. cerevisiae) is regulated by the level of glucose in the medium. Glucose is known to inhibit respiration by repressing key enzymes in the respiratory chain. We present evidence that the early events in this inhibition include the closure of VDAC channels, the primary pathway for metabolite flow across the outer membrane. Aluminum hydroxide is known to inhibit the closure of VDAC. Addition of aluminum acetylacetonate to yeast cells, which should elevate the aluminum hydroxide concentrations in the cytoplasm, caused the inhibition of cell respiration by glucose to be delayed for up to 100 min. No significant effect of aluminum was observed in cells grown on glycerol. Yeast cells lacking the VDAC gene were also unresponsive to the addition of aluminum salt in the presence of glucose. Therefore, the closure of VDAC channels may be an early step in the inhibition of the respiration of yeast by glucose.
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Affiliation(s)
- M Ahmadzadeh
- Department of Zoology, University of Maryland, College Park 20742, USA
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8
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Gilbert ME, Shafer TJ. In vitro exposure to aluminum does not alter long-term potentiation or glutamate release in rat hippocampal slices. Neurotoxicol Teratol 1996; 18:175-80. [PMID: 8709929 DOI: 10.1016/0892-0362(95)02017-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Aluminum has been reported to inhibit long-term potentiation (LTP) following in vivo administration and decrease glutamate release following in vitro exposure. Because glutamate release is critical for synaptic transmission and the development and maintenance of LTP in the hippocampus, we examined the effects of aluminum chloride (AlCl3) on depolarization-induced glutamate release and LTP in rat hippocampal slices. The effects of AlCl3 on [14C]glutamate release were examined by incubation of slices in depolarizing (56 mM)K+ buffer solution in the absence or presence of 2 mM CaCl2. After 15 min depolarization, AlCl3 (100-1000 microM) did not significantly affect Ca(2+)-dependent [14C]glutamate release from slices, whereas a known Ca2+ channel blocker (100 microM CdCl2) decreased Ca(2+)-dependent [14C]glutamate release by approximately 50%. In contrast to a previous report, acute exposure to AlCl3 was without effect on depolarization-dependent glutamate release. LTP of the population spike (PS) in CA1 of hippocampus was induced by the delivery of stimulus trains to the stratum radiatum. LTP of the PS was observed in both control slices and slices bathed in solution containing 100 microM AlCl3. Neither the magnitude nor longevity (measured up to 1 h posttrain) of LTP distinguished control from aluminum-exposed slices. The lack of sensitivity in rat to the encephalopathic changes induced by aluminum, or methodological differences in exposure conditions may account for the lack of effect of aluminum on in vitro LTP in rat hippocampus.
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Affiliation(s)
- M E Gilbert
- Neurotoxicology Division (MD-74B), Health Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA
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9
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Colombini M, Blachly-Dyson E, Forte M. VDAC, a channel in the outer mitochondrial membrane. ION CHANNELS 1996; 4:169-202. [PMID: 8744209 DOI: 10.1007/978-1-4899-1775-1_5] [Citation(s) in RCA: 175] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- M Colombini
- Department of Zoology, University of Maryland, College Park 20742, USA
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10
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Liu MY, Torgrimson A, Colombini M. Characterization and partial purification of the VDAC-channel-modulating protein from calf liver mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1185:203-12. [PMID: 7513187 DOI: 10.1016/0005-2728(94)90211-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The mitochondrial channel, VDAC, mediates metabolic flux across the mitochondrial outer membrane. When reconstituted into planar phospholipid membranes, VDAC is voltage-dependent, existing in multiple conformational states with different selectivities and permeabilities. At low membrane potentials, these channels are in the open state and are anion-selective. VDAC channels switch to lower-conductive closed states at high membrane potentials. The VDAC modulator, a soluble mitochondrial protein, has been demonstrated to dramatically increase the voltage dependence of VDAC channels and induce the channels to enter closed states even at low membrane potentials. We have isolated and partially purified this modulating protein and the activity is associated with a 54 kDa protein on SDS-PAGE. Under native reduced conditions the activity eluted around 100 kDa from a gel filtration column. As little as 200 ng/ml of the partially purified protein was sufficient to modulate reconstituted VDAC channels. This protein had a pI of 5.1. A second activity with a pI of 4.8 was far more potent, making VDAC-channel-containing membranes virtually non-conductive in some experiments. The effects of both modulator activities could be completely reversed by the addition of pronase. Simple perfusion of the chamber did not reverse the effect of the modulator on VDAC. By controlling the gating of VDAC channels, the VDAC modulator could play an important role in regulating cellular metabolism.
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Affiliation(s)
- M Y Liu
- Department of Zoology, University of Maryland, College Park 20742
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Colombini M. Chapter 4 Anion Channels in the Mitochondrial Outer Membrane. CURRENT TOPICS IN MEMBRANES 1994. [DOI: 10.1016/s0070-2161(08)60819-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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12
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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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13
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Liu MY, Colombini M. Regulation of mitochondrial respiration by controlling the permeability of the outer membrane through the mitochondrial channel, VDAC. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1098:255-60. [PMID: 1730010 DOI: 10.1016/s0005-2728(05)80344-5] [Citation(s) in RCA: 86] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mitochondrial functions depend not only on the properties of the particular enzyme systems, but also on the continual flux of metabolites between the cytoplasm and mitochondrial spaces. We report the results of experiments that strongly indicate that a soluble mitochondrial protein can regulate mitochondrial respiration by reducing the permeability of the outer membrane. This protein is known as the VDAC modulator because it induces the outer mitochondrial membrane channel, VDAC, to close. When added to intact mitochondria, the modulator reduces the ADP-stimulated respiration. This inhibition can be prevented by damaging the outer membrane prior to modulator addition. Another mitochondrial activity, adenylate kinase, is reduced by 40% by the addition of the VDAC modulator to intact mitochondria. Again, damaging the outer membrane removed the modulator effect. Dextran sulfate, an artificial polyanion that acts on VDAC channels in a similar way to the VDAC modulator, has the same effects on intact mitochondria. The findings correlate well with observations of the actions of the VDAC modulator on reconstituted VDAC channels, in which the modulator induces the channel to enter a very low conductive state. The ability of a mitochondrial protein to regulate mitochondrial activities by reducing the permeability of the outer membrane further fuels the hypothesis that this membrane participates in the overall regulation of mitochondrial functions.
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Affiliation(s)
- M Y Liu
- Department of Zoology, University of Maryland, College Park, MD
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Yoshino M, Murakami K. Aluminum: a pH-dependent inhibitor of NADP-isocitrate dehydrogenase from porcine heart. Biometals 1992; 5:217-21. [PMID: 1463928 DOI: 10.1007/bf01061221] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Aluminum showed a pH-dependent inhibitory effect on NADP-isocitrate dehydrogenase from porcine heart. Aluminum ions (Al3+) acted as a partial competitive inhibitor of the enzyme with respect to the substrate threo-Ds-isocitrate and inhibited the enzyme non-competitively with respect to NADP at pH 6.85. Fractional velocity plot analysis showed the Ki of the enzyme for aluminum ions to be 0.88 microM. When pH was elevated to 8.0, aluminum ions, which occur as a form of the Al(OH)4- anion, acted as partial uncompetitive and non-competitive inhibitors of the enzyme with respect to the substrates isocitrate and NADP, respectively. The Kí of the enzyme was determined to be 5.64 microM at pH 8.0 by fractional velocity plot analysis. The inhibition of NADP-isocitrate dehydrogenase by two forms of aluminum ions may explain aluminum toxicity in various tissues and organs.
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Affiliation(s)
- M Yoshino
- Department of Genetics, Institute for Developmental Research, Aichi, Japan
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15
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Zhang DW, Colombini M. Group IIIA-metal hydroxides indirectly neutralize the voltage sensor of the voltage-dependent mitochondrial channel, VDAC, by interacting with a dynamic binding site. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1025:127-34. [PMID: 1694685 DOI: 10.1016/0005-2736(90)90089-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The voltage-dependent, anion-selective mitochondrial channel, VDAC, undergoes two different conformational changes from the open to a closed state under positive and negative applied electric fields. Micromolar quantities of aluminum hydroxide and other metal trihydroxides have recently been shown to be able to inhibit this voltage-dependent closure (Dill et al. (1987) J. Membr. Biol. 99, 187-196; Zhang and Colombini (1989) Biochim. Biophys. Acta 991, 68-78). It was suggested that the inhibition results from the neutralization of the positively charged voltage sensors by the metal species. In the present study, the dynamics of the metal-binding site accompanying channel closure was investigated by adding In(OH)3 to only one side of the membrane and examining its effect on the channel's gating processes. Indium added to open channels inhibited channel closure only when the metal-containing side was on the lower potential side of the applied field. If indium was added only to the higher-potential side, the channels closed and tended to remain closed after the field was abolished. The addition of metal hydroxide after closing the channels with a negative potential on the metal side did not result in channel re-opening as would be expected for sensor neutralization. Inhibition occurred immediately, however, if the channels were first allowed to open briefly. The closed-state selectivity seemed to be very similar in the absence or presence of the metal, indicating that the metal-binding sites are not located within the pore of the channel in the closed conformation. The results are consistent with a voltage-dependent translocation across the membrane of each of two metal-binding sites on VDAC. This translocation is tightly coupled with channel opening and closing.
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Affiliation(s)
- D W Zhang
- Department of Zoology, University of Maryland, College Park 20742
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