Porins in mitochondria

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Federal government websites often end in. The site is secure. Preview improvements coming to the PMC website in October Learn More or Try it out now. Porin, also termed the voltage-dependent anion channel, is the most abundant protein of the mitochondrial outer membrane. The process of import and assembly of the protein is known to be dependent on the surface receptor Tom20, but the requirement for other mitochondrial proteins remains controversial.

Porins in mitochondria

Mitochondria import the vast majority of their proteins via dedicated protein machineries. The translocase of the outer membrane TOM complex forms the main entry site for precursor proteins that are produced on cytosolic ribosomes. Subsequently, different protein sorting machineries transfer the incoming preproteins to the mitochondrial outer and inner membranes, the intermembrane space, and the matrix. In this review, we highlight the recently discovered role of porin, also termed voltage-dependent anion channel VDAC , in mitochondrial protein biogenesis. Porin forms the major channel for metabolites and ions in the outer membrane of mitochondria. Two different functions of porin in protein translocation have been reported. First, it controls the formation of the TOM complex by modulating the integration of the central receptor Tom22 into the mature translocase. Second, porin promotes the transport of carrier proteins toward the carrier translocase TIM22 complex , which inserts these preproteins into the inner membrane. Therefore, porin acts as a coupling factor to spatially coordinate outer and inner membrane transport steps. Thus, porin links metabolite transport to protein import, which are both essential for mitochondrial function and biogenesis. Work included in this study has been performed in partial fulfillment of the requirements for the doctoral thesis of A.

Further evidence comes from cell lines and knock-out mice lacking porin isoforms singly or in combination.

Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. They are present in the outer membrane of gram-negative bacteria and some gram-positive mycobacteria mycolic acid-containing actinomycetes , the outer membrane of mitochondria , and the outer chloroplast membrane outer plastid membrane. This means that the nonpolar residues face outward so as to interact with the nonpolar lipids of outer membrane , whereas the polar residues face inwards into the center of the beta barrel to create the aqueous channel. The specific amino acids in the channel determine the specificity of the porin to different molecules. The individual strands are joined together by loops and turns.

Metrics details. Mitochondrial porins, or voltage-dependent anion-selective channels VDAC allow the passage of small molecules across the mitochondrial outer membrane, and are involved in complex interactions regulating organellar and cellular metabolism. Numerous organisms possess multiple porin isoforms, and initial studies indicated an intriguing evolutionary history for these proteins and the genes that encode them. In this work, the wealth of recent sequence information was used to perform a comprehensive analysis of the evolutionary history of mitochondrial porins. Fungal porin sequences were well represented, and newly-released sequences from stramenopiles, alveolates, and seed and flowering plants were analyzed. A combination of Neighbour-Joining and Bayesian methods was used to determine phylogenetic relationships among the proteins.

Porins in mitochondria

Federal government websites often end in. The site is secure. 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. 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.

Dcccd ecampus

Using an assay established to monitor the assembly of in vitro—imported porin into preexisting porin complexes we have shown that besides Tom20, the biogenesis of porin depends on the central receptor Tom22, as well as Tom5 and Tom7 of the general import pore complex translocase of the outer mitochondrial membrane [TOM] core complex. The genomes of many eukaryotic organisms, in particular of mammals and plants, code very often for several porins with yet not fully understood functions Anflous and Craigen, ; Pinto and Messina, ; Graham and Craigen, ; Tateda et al. Pagliarini, D. If the first scenario applies it would suggest that VDAC duplication events in part paralleled the requirement for more specialized forms of VDACs as eukaryotes evolved into more complex multicellular or multi-tissue forms. Cell Biochem. Manual comparisons of the amino-terminal regions of the protein sequences visualized in GeneDoc [ 64 ] did reveal motifs common to most members of the largest phylogenetic groups: plants, fungi and animals Fig. Koonin, E. The minus - indicates that the sequence was incomplete and thus the GLK and eukaryotic porin motifs could not be identified. PubMed Abstract Google Scholar. Nargang: ac. Porins are primarily involved in passively transporting hydrophilic molecules of various sizes and charges across the membrane. Important for this could be the close apposition of mitochondrial inner and outer membrane that a voltage across the outer membrane is induced via capacitive coupling of inner and outer membranes, in which also the folding of the inner membrane may be involved Benz, ; Mannella et al. In the present study, we performed a detailed characterization of porin import in Neurospora crassa and the yeast Saccharomyces cerevisiae to directly determine the role of GIP and individual Tom proteins in import of porin.

Metrics details. Biological energy conversion in mitochondria is carried out by the membrane protein complexes of the respiratory chain and the mitochondrial ATP synthase in the inner membrane cristae. Recent advances in electron cryomicroscopy have made possible new insights into the structural and functional arrangement of these complexes in the membrane, and how they change with age.

Voltage-dependent anion-selective channel 1 VDAC1 --a mitochondrial protein, rediscovered as a novel enzyme in the plasma membrane. Dynamics of the TOM complex of mitochondria during binding and translocation of preproteins. In the present study, we performed a detailed characterization of porin import in Neurospora crassa and the yeast Saccharomyces cerevisiae to directly determine the role of GIP and individual Tom proteins in import of porin. Cell, 21 , — Moreover, the porin precursor can be cross-linked to Tom20, Tom22, and Tom40 on its import pathway. In a first step, mitochondria were lysed by an osmotic shock and the total mitochondrial membranes were obtained by centrifugation. Anion Carriers of Mitochondrial Membranes. Bibcode : Sci Samples were separated by SDS-PAGE, blotted onto nitrocellulose, and proteins from different mitochondrial compartments were detected using specific antisera. In the case of plant porins, also a second maximum was observed at 1. Peixoto, P. The combination of the cations and anions was chosen to show the voltage dependence of human eukaryotic porin 1 hVDAC1, Porin 31HL in dependence of cations and anions of different mobility because this provides not only some information on voltage dependence but also on ion selectivity of the open and closed states of the pore. Our results place the stramenopile VDACs as outliers to the three main clades. Rampelt, H. Cross-Linking of the Porin Precursor to Tom20, Tom22, and Tom40 To obtain independent evidence for the involvement of components of the GIP complex in porin import, we performed cross-linking of porin precursor molecules during the import process.