The Voltage-Dependent Anion Selective Channel 1 (VDAC1) Topography in the Mitochondrial Outer Membrane as Detected in Intact Cell (original) (raw)
Related papers
Biochemistry, 2015
The Voltage-Dependent Anion Channel (VDAC) is the main mitochondrial porin allowing the exchange of ions and metabolites between the cytosol and the mitochondrion. In addition, VDAC was found to actively interact with proteins playing a fundamental role in the regulation of apoptosis and being of central interest in cancer research. VDAC is a large transmembrane β barrel channel, whose N terminal helical fragment adheres to the channel interior, partially closing the pore. This fragment is considered to play a key role for protein stability and function as well as for the interaction with apoptosis related proteins. Three VDAC isoforms are differently expressed in higher eukaryotes, for which distinct and complementary roles are proposed. In the present work, the folding propensity of their N-terminal fragments has been compared. By using multiple spectroscopic techniques, and complementing the experimental results with theoretical computer-assisted approaches, their conformational ...
Voltage-dependent anion channels: the wizard of the mitochondrial outer membrane
Biological Chemistry, 2014
Voltage dependent anion channels (VDACs) are the most abundant proteins in the outer mitochondrial membrane. Although they are essential in metabolite exchange, cell defense and apoptosis, the molecular mechanism of these VDAC-mediated processes remains elusive. Here we review recent progress in terms of VDACs’ structure and regulation, with a special focus on the molecular aspects of gating and the interaction with effector proteins.
International Journal of Biochemistry & Cell Biology, 2005
The eukaryotic porin or voltage-dependent anion-selective channel (VDAC1) is a pore-forming protein discovered twenty five years ago in the mitochondrial outer membrane. Its gene in eukaryotes is known, but its tertiary structure has never been solved. Structure predictions highlight the presence of several amphipathic -strands possibly organised in a -barrel. VDAC1 has recently been described as being a NADH:ferricyanide reductase in the plasma membrane. There it affects the regulation of cell growth and death. Physiological cell death (apoptosis) has become a major research focus of biomedical research. Regulation of the enzyme will have impacts on cancer and autoimmune diseases (insufficient apoptosis) as well as neurodegenerative diseases (excessive apoptosis). VDAC1 in the plasma membrane establishes a novel level of apoptosis regulation putatively via its redox activity.
Conformational Changes in the Mitochondrial Channel Protein, VDAC, and Their Functional Implications
Journal of Structural Biology, 1998
The voltage-dependent, anion-selective channel (VDAC) is generally considered the main pathway for metabolite diffusion across the mitochondrial outer membrane. It also interacts with several mitochondrial and cytosolic proteins, including kinases and cytochrome c. Sequence analysis and circular dichroism suggest that the channel is a bacterial porin-like beta-barrel. However, unlike bacterial porins, VDAC does not form tight trimeric complexes and is easily gated (reversibly closed) by membrane potential and low pH. Circular dichroism indicates that the protein undergoes a major conformational change at pH < 5, involving decreased beta-sheet and increased alpha-helical content. Electron microscopy of two-dimensional crystals of fungal VDAC provides direct information about the size and shape of its lumen and suggests that the N-terminal domain forms a mobile alpha-helix. It is proposed that the N-terminal domain normally resides in a groove in the lumen wall and that gating stimuli favor its displacement, destabilizing the putative beta-barrel. Partial closure would result from subsequent larger-scale structural rearrangements in the protein, possibly corresponding to the conformational change observed at pH < 5.
Journal of molecular …, 2010
Voltage-dependent anion channels (VDAC) are pore-forming proteins found in the outer mitochondrial membrane of eukaryotes. VDACs are known to play an essential role in cellular metabolism and in early stages of apoptosis. In mammals, three VDAC isoforms have been identified. A proteomic approach was exploited to study the expression of VDAC isoforms in rat, bovine, and chicken brain mitochondria. Given the importance of mitochondrially bound hexokinase in regulation of aerobic glycolysis in brain, we studied the possibility that differences in the relative expression of VDAC isoforms may be a factor in determining the species-dependent ratio of type A/type B hexokinase binding sites on brain mitochondria. The spots were characterized, and the signal intensities among spots were compared. VDAC1 was the most abundantly expressed of the three isoforms. Moreover the expression of VDAC1 plus VDAC2 was significantly higher in bovine than in rat brain. Chicken brain mitochondria showed the highest VDAC1 expression and the lowest of VDAC2. Bovine brain mitochondria had the highest VDAC2 levels. We concluded that the nature of hexokinase binding site is not determined by the expression of a single VDAC isoform.
The mitochondrial channel VDAC has a cation-selective open state
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2005
The mitochondrial channel VDAC is known to have two major classes of functional states, a large conductance "open" state that is anion selective, and lower conductance substates that are cation selective. The channel can reversibly switch between open and half-open states, with the latter predominant at increasing membrane voltages of either polarity. We report the presence of a new functional state of VDAC, a cationselective state with conductance approximately equal to that of the canonical open state. This newly described state of VDAC can be reached from either the half-open cation-selective state or from the open anion-selective state. The latter transition implies that a mechanism exists for selectivity gating in VDAC that is separate from partial closure, which may be relevant to the physiological regulation of this channel and mitochondrial outer membrane permeability. Biochimica et Biophysica Acta 1710 (2005) 96 -102 http://www.elsevier.com/locate/bba Abbreviations: E rev , equilibrium reversal potential; IMS, intermembrane space; TOM, translocase outer membrane; VDAC, voltage dependent anionselective channel ⁎ Corresponding author. Fax: +1 212 995 4087.
Journal of Biological Chemistry, 2006
Cell function depends on the distribution of cytosolic and mitochondrial factors across the outer mitochondrial membrane (OMM). Passage of metabolites through the OMM has been attributed to the voltage-dependent anion-selective channel (VDAC), which can form a large conductance and permanently open a channel in lipid bilayers. However, recent data indicate that the transport of metabolites through the OMM is controlled in the cells. Recognizing that the bilayer studies had been commonly conducted at supraphysiological [Ca 2؉ ] and [K ؉ ], we determined the effect of Ca 2؉ on VDAC activity. In liposomes, the purified VDAC displays Ca 2؉-dependent control of the molecular cutoff size and shows Ca 2؉-regulated Ca 2؉ permeability in the physiological [Ca 2؉ ] range. In bilayer experiments, at submicromolar [Ca 2؉ ], the purified VDAC or isolated OMM does not show sustained large conductance but rather exhibits gating between a nonconducting state and various subconductance states. Ca 2؉ addition causes a reversible increase in the conductance and may evoke channel opening to full conductance. Furthermore, single cell imaging data indicate that Ca 2؉ may facilitate the cation and ATP transport across the OMM. Thus, the VDAC gating is dependent on the physiological concentrations of cations, allowing the OMM to control the passage of ions and some small molecules. The OMM barrier is likely to decrease during the calcium signal.
Toward the molecular structure of the mitochondrial channel, VDAC
Journal of Bioenergetics and Biomembranes, 1992
A summary is presented of the most recent information about the structure and mechanism of closure of the mitochondrial channel, VDAC. Considerable information has come from studies involving electron microscopy of two-dimensional crystals and from electrophysiological studies of wild-type channels and site-directed mutants. Available evidence points to a/~-barrel as the basic structural model for VDAC. Two models for voltage-or effector-induced closure have been proposed, the first involving removal of strands from the wall of the pore, the second invoking movement of protein domains into the lumen. Experimental strategies to resolve the actual mechanism are presented.
Journal of Biological Chemistry, 2003
The relevance of the mitochondrial permeability transition pore (PTP) in Ca 2؉ homeostasis and cell death has gained wide attention. Yet, despite detailed functional characterization, the structure of this channel remains elusive. Here we report on a new class of inhibitors of the PTP and on the identification of their molecular target. The most potent among the compounds prepared, Ro 68-3400, inhibited PTP with a potency comparable to that of cyclosporin A. Since Ro 68-3400 has a reactive moiety capable of covalent modification of pro-
Journal of Structural Biology, 1999
Overexpressed human voltage-dependent anionselective channel VDAC or porin from mitochondrial outer membranes has been purified to homogeneity. Electron microscopic analysis of VDAC in detergent solution revealed a uniform particle population consisting of porin monomers. After dialysis of detergent-solubilized porin in the presence of dimyristoylphosphatidylcholine at lipid-to-protein ratios between 0.2 and 0.5 (percentage by weight), mostly multilamellar crystals were obtained. Crystals adsorbed to carbon films flattened during negative staining and air-drying and exhibited different structural features due to differences in the vertical stacking of several crystalline layers, each consisting of one membrane bilayer. Adsorbed, frozenhydrated multilamellar membrane crystals revealed uniform diffraction patterns with sharp diffraction spots extending to 8.2 Å. The surface structure of VDAC was reconstructed from freeze-dried and unidirectionally metal-shadowed crystals. Major protein protrusions were observed from two VDAC monomers present in the unit cell. Differences in the surface structural features indicate alternate orientations of VDAC molecules with respect to the lipid bilayer, allowing the simultaneous imaging of both the cytosolic and intramitochondrial surfaces. Each VDAC molecule consists of a pore lumen with a diameter of 17-20 Å surrounded by a protein rim of nonuniform height, suggesting an asymmetrical distribution of protein mass around the diffusion channels. 1999 Academic Press