Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “inner membrane complex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed1977

The development of oxidative enzymes in rat liver mitochondria.

During early postnatal development there was an increase in the specific activity of a number of oxidative enzymes localized on the outer and inner mitochondrial membrane. The succinic oxidase complex of the inner mitochondrial membrane, whose activity in 1-day-old rats was 50% of the value in adult animals, attained the maximum on about the 10th day after birth. Activity of the choline and the proline oxidase complex, both of which are also localized in the inner mitochondrial membrane, was minimal in 1-day-old rats and went on rising after the 10th day. Rotenone-insensitive NADH-cytochrome c reductase activity, which is localized on the outer mitochondrial membrane, remained stable up to the 10th day, and rose between the 10th and the 90th day. Developmental changes in monoaminooxidase activity, which is likewise localized on the outer mitochondrial membrane, followed a similar course to the choline and proline oxidase complexes. The amount of cytochromes a+alpha3 and cytochrome b in isolated mitochondria did not alter during development. The protein spectrum of the mitochondrial particles, determined by polyacrylamide gel electrophoresis in sodium dodecyl sulphate, likewise displayed no marked changes during postnatal development. The above findings show that the metabolic functions of the mitochondria mature during development and that changes in the different enzymes have their own characteristic time course.

Animals↗
PubMed2002

Protein import into mitochondria of Neurospora crassa.

Biogenesis of mitochondria requires import of several hundreds of different nuclear-encoded preproteins needed for mitochondrial structure and function. Import and sorting of these preproteins is a multistep process facilitated by complex proteinaceous machineries located in the mitochondrial outer and inner membranes. The translocase of the mitochondrial outer membrane, the TOM complex, comprises receptors which specifically recognize mitochondrial preproteins and a protein conducting channel formed by TOM40. The TOM complex is able to insert resident proteins into the outer membrane and to translocate proteins into the intermembrane space. For import of inner membrane or matrix proteins, the TOM complex cooperates with translocases of the inner membrane, the TIM complexes. During the past 30 years, intense research on fungi enabled the identification and mechanistic characterization of a number of different proteins involved in protein translocation. This review focuses on the contributions of the filamentous fungus Neurospora crassa to our current understanding of mitochondrial protein import, with special emphasis on the structure and function of the TOM complex.

Carrier Proteins↗
PubMed1995

Protein complex within Escherichia coli inner membrane. TolA N-terminal domain interacts with TolQ and TolR proteins.

The TolA, TolB, TolQ, and TolR proteins are involved in maintaining the integrity of the Escherichia coli outer membrane and in the import of group A colicins and filamentous phage DNA. TolA, TolQ, and TolR are localized in the inner membrane while TolB is periplasmic, although a small amount of membrane-associated TolB is always found. In vivo cross-linking experiments with formaldehyde were performed in order to determine the proteins interacting with TolA. In wild-type strains, two specific complexes of 65 and 71 kDa, comprising TolA, were identified. These complexes were absent in a tolQ strain, while only the 65-kDa complex was absent in a tolR strain. When the tol strains were transformed with plasmids encoding TolR or TolQ, the specific complexes were restored. Moreover, immunoprecipitation experiments with the antiserum directed against TolA indicated that TolQ and TolR were co-immunoprecipitated with TolA after cross-linking. These data demonstrate that TolA interacts directly with TolR and TolQ. Two truncated TolA proteins devoid of either the C-terminal or the central domains of the protein were subjected to in vivo cross-linking. Since these two TolA derivatives still formed specific complexes with TolR derivatives still formed specific complexes with TolR and TolQ, we concluded that the TolA N-terminal domain interacted with these proteins.

Bacterial Proteins↗
PubMed1995

The MIM complex mediates preprotein translocation across the mitochondrial inner membrane and couples it to the mt-Hsp70/ATP driving system.

We have identified a complex in mitochondria that functions as a part of the preprotein import machinery of the inner membrane (MIM complex). Two known components, MIM23 and MIM17, and two novel components, MIM33 and MIM14, were found as constituents of this complex. In the presence of a translocating chain, the outer membrane import machinery (MOM complex) and the MIM complex form translocation contact sites. On the matrix side, the MIM complex is associated with the mt-Hsp70-MIM44 system. We propose a structure of the import machinery in which the MIM complex constitutes a proteinaceous channel that accepts preproteins from the MOM complex, facilitates their reversible transmembrane movement, and mediates unidirectional transport by linkage to the ATP-dependent mt-Hsp70-MIM44 system.

Adenosine Triphosphate↗
PubMed1978

The mitochondrial localization of coproporphyrinogen III oxidase.

The location of coproporphyrinogen III oxidase in mitochondria was studied in rat liver by using the digitonin method or hypo-osmotic media for fractionation. The enzyme was found in the intermembrane space with a fraction loosely bound to the inner membrane. This fraction was released by washing the inner-membrane-matrix complex with alkaline solutions or solutions of high ionic strength. The enzyme in both fractions had the same Km (0.16 micrometer) for coproporphyrinogen III. When incubation was performed in a medium that avoided destruction of enzyme membrane binding, a dramatic increase in activity was observed after sonication of whole mitochondria or of the inner-membrane-matrix complex.

Animals↗
PubMed1985

Independent lateral diffusion of cytochrome bc1 complex and cytochrome oxidase in the mitochondrial inner membrane.

Distinct fluorophores have been conjugated to antibodies for cytochrome bc1 complex and cytochrome oxidase, two integral electron transferring proteins in the mitochondrial inner membrane. Addition of these fluorescent antibodies to preparations of mitochondrial inner membranes followed by appropriate secondary antibodies causes distinct and independent aggregation of the two cytochrome proteins. These results reveal that both cytochrome bc1 complex and cytochrome oxidase diffuse laterally in the membrane plane independent of one another consistent with the random collision model for electron transport in the mitochondrial inner membrane.

Animals↗
PubMed2004

The role of Hot13p and redox chemistry in the mitochondrial TIM22 import pathway.

The small Tim proteins in the mitochondrial intermembrane space participate in the TIM22 import pathway for assembly of the inner membrane. Assembly of the small TIM complexes requires the conserved "twin CX3C" motif that forms juxtapositional intramolecular disulfide bonds. Here we identify a new intermembrane space protein, Hot13p, as the first component of a pathway that mediates assembly of the small TIM complexes. The small Tim proteins require Hot13p for assembly into a 70-kDa complex in the intermembrane space. Once assembled the small TIM complexes escort hydrophobic inner membrane proteins en route to the TIM22 complex. The mechanism by which the small Tim proteins bind and release substrate is not understood, and we investigated the affect of oxidant/reductant treatment on the TIM22 import pathway. With in organello import studies, oxidizing agents arrest the ADP/ATP carrier (AAC) bound to the Tim9p-Tim10p complex in the intermembrane space; this productive intermediate can be chased into the inner membrane upon subsequent treatment with reductant. Moreover, AAC import is markedly decreased by oxidant treatment in Deltahot13 mitochondria and improved when Hot13p is overexpressed, suggesting Hot13p may function to remodel the small TIM complexes during import. Together these results suggest that the small TIM complexes have a specialized assembly pathway in the intermembrane space and that the local redox state of the TIM complexes may mediate translocation of inner membrane proteins.

Amino Acid Sequence↗
PubMed2000

Targeting of proteins to mitochondria.

A clear picture has emerged over the past years on how a 'classic' mitochondrial protein, like subunit IV of cytochrome c oxidase, might be targeted to mitochondria. The targeting and subsequent import process involves the commitment of the TOM (translocase in the outer mitochondrial membrane) receptor complex on the mitochondrial surface, a TIM (translocase in the inner mitochondrial membrane) translocation complex in the mitochondrial inner membrane, and assorted chaperones and processing enzymes within the organelle. Recent work suggests that while very many mitochondrial precursor proteins might follow this basic targeting pathway, a large number have further requirements if they are to be successfully imported. These include ribosome-associated factors and soluble factors in the cytosol, soluble factors in the mitochondrial intermembrane space, an additional TIM translocase in the inner membrane and a range of narrow specificity assembly factors in the inner membrane. This review is focused on the targeting of proteins up to the stage at which they enter the TOM complex in the outer membrane.

Carrier Proteins↗
PubMed2001

YidC, an assembly site for polytopic Escherichia coli membrane proteins located in immediate proximity to the SecYE translocon and lipids.

Like its mitochondrial homolog Oxa1p, the inner membrane protein YidC of Escherichia coli is involved in the integration of membrane proteins. We have analyzed individual insertion steps of the polytopic E. coli membrane protein MtlA targeted as ribosome-nascent chain complexes to inner membrane vesicles. YidC can accommodate at least the first two transmembrane segments of MtlA at the protein lipid interface and retain them even though the length of the nascent chain would amply allow insertion into membrane lipids. An even longer insertion intermediate of MtlA is described that still has the first transmembrane helix bound to YidC while the third contacts SecE and YidC during integration. Our findings suggest that YidC forms a contiguous integration unit with the SecYE translocon and functions as an assembly site for polytopic membrane proteins mediating the formation of helix bundles prior to their release into the membrane lipids.

Bacterial Proteins↗
PubMed1983

A yeast mitochondrial inner membrane 30K hydrophobic protein: comparison with subunit 32K of the cytochrome BC 1 complex.

A yeast mitochondrial inner membrane hydrophobic protein 30K has been isolated and compared to subunit 32K of the yeast cytochrome bc 1 complex. Both proteins are translated on mitochondrial ribosomes, have nearly the same molecular weight and similar aminoacid compositions. Comparison was carried out by immunological techniques with specific antibodies, and by studying 3 yeast strains having mutations in the COB region of the mitochondrial DNA. Results show that the two proteins are not identical.

Electron Transport Complex III↗
PubMed2000

Protein translocation into mitochondria: the role of TIM complexes.

Import of nuclear-encoded mitochondrial preproteins is mediated by a general translocase in the outer membrane, the TOM complex, and by two distinct translocases in the mitochondrial inner membrane, the TIM23 complex and the TIM22 complex. Both TIM complexes cooperate with the TOM complex but facilitate import of different classes of precursor proteins. Precursors with an N-terminal presequence are imported via the TIM23 complex, whereas mitochondrial carrier proteins require the TIM22 complex for insertion into the inner membrane. This review discusses recent advances in understanding the structure and function of the translocases of the inner membrane and the possible role of Tim proteins in the development of the Mohr-Tranebjaerg syndrome, a mitochondrial disorder leading to neurodegeneration.

Animals↗
PubMed2006

Bactericidal activity of both secreted and nonsecreted microcin E492 requires the mannose permease.

Microcin E492 (MccE492) is a bactericidal protein secreted by Klebsiella pneumoniae that is active against various species of Enterobacteriaceae. Interaction of MccE492 with target cells leads to the depolarization and permeabilization of their inner membranes. Several MccE492-specific proteins are required for the maturation and secretion of active MccE492. Surprisingly, the expression of only MceA, the polypeptide backbone of MccE492, is shown here to be toxic by itself. We refer to this phenomenon as endogenous MceA bactericidal activity to differentiate it from the action of extracellularly secreted MccE492. The toxicity of endogenous MceA is enhanced by an efficient targeting to the inner membrane. However, a periplasmic intermediate state is not required for MceA toxicity. Indeed, endogenous MceA remains fully active when it is fused to thioredoxin-1, a fast-folding protein that promotes retention of the C terminus of MceA in the cytoplasm. The C-terminal domain of MccE492 is required only for delivery from the extracellular environment to the periplasm, and it is not required for inner membrane damage. A common component is absolutely essential for the bactericidal activity of both endogenous MceA and extracellular MccE492. Indeed, toxicity is strictly dependent on the presence of ManYZ, an inner membrane protein complex involved in mannose uptake. Based on these findings, we propose a new model for cell entry, inner membrane insertion, and toxic activity of MccE492.

Anti-Bacterial Agents↗
PubMed2004

Cross-linking ATP synthase complexes in vivo eliminates mitochondrial cristae.

We have used the tetrameric nature of the fluorescent protein DsRed to cross-link F(1)F(O)-ATPase complexes incorporating a subunit gamma-DsRed fusion protein in vivo. Cells expressing such a fusion protein have impaired growth relative to control cells. Strikingly, fluorescence microscopy of these cells revealed aberrant mitochondrial morphology. Electron microscopy of cell sections revealed the absence of cristae and multiple layers of unfolded inner mitochondrial membrane. Complexes recovered from detergent lysates of mitochondria were present largely as tetramers. Co-expression of 'free' DsRed targeted to the mitochondria reduced F(1)F(O)-ATPase oligomerisation and partially reversed the impaired growth and abnormal mitochondrial morphology. We conclude that the correct arrangement of F(1)F(O)-ATPase complexes within the mitochondrial inner membrane is crucial for the genesis and/or maintenance of mitochondrial cristae and morphology. Our findings further suggest that F(1)F(O)-ATPase can exist in oligomeric associations within the membrane during respiratory growth.

Cell Division↗
PubMed1999

Genetic and structural characterization of the human mitochondrial inner membrane translocase.

Translocation of nuclear-encoded mitochondrial preproteins is mediated by translocases in the outer and inner membranes. In the yeast Saccharomyces cerevisiae, translocation of preproteins into the matrix requires the membrane proteins Tim23, Tim17 and Tim44, which drive translocation in cooperation with mtHsp70 and its co-chaperone Mge1p. We have cloned and functionally analyzed the human homologues of Tim17, Tim23 and Tim44. In contrast to yeast, two TIM17 genes were found to be expressed in humans. TIM44, TIM23 and TIM17a genes were mapped to chromosomes 19p13.2-p13.3, 10q11. 21-q11.23 and 1q32. The TIM17b gene mapped to Xp11.23, near the fusion point where an autosomal region was proposed to have been added to the "ancient" part of the X chromosome about 80-130 MY ago. The primary sequences of the two proteins, hTim17a and hTim17b, are essentially identical, significant differences being restricted to their C termini. They are ubiquitously expressed in fetal and adult tissues, and both show expression levels comparable to that of hTim23. Biochemical characterization of the human Tim components revealed that hTim44 is localized in the matrix and, in contrast to yeast, only loosely associated with the inner membrane. hTim23 is organized into two distinct complexes in the inner membrane, one containing hTim17a and one containing hTim17b. Both TIM complexes display a native molecular mass of 110 kDa. We suggest that the structural organization of TIM23.17 preprotein translocases is conserved from low to high eukaryotes.

Adult↗
PubMed2003

Mitochondria use different mechanisms for transport of multispanning membrane proteins through the intermembrane space.

The mitochondrial inner membrane contains numerous multispanning integral proteins. The precursors of these hydrophobic proteins are synthesized in the cytosol and therefore have to cross the mitochondrial outer membrane and intermembrane space to reach the inner membrane. While the import pathways of noncleavable multispanning proteins, such as the metabolite carriers, have been characterized in detail by the generation of translocation intermediates, little is known about the mechanism by which cleavable preproteins of multispanning proteins, such as Oxa1, are transferred from the outer membrane to the inner membrane. We have identified a translocation intermediate of the Oxa1 preprotein in the translocase of the outer membrane (TOM) and found that there are differences from the import mechanisms of carrier proteins. The intermembrane space domain of the receptor Tom22 supports the stabilization of the Oxa1 intermediate. Transfer of the Oxa1 preprotein to the inner membrane is not affected by inactivation of the soluble TIM complexes. Both the inner membrane potential and matrix heat shock protein 70 are essential to release the preprotein from the TOM complex, suggesting a close functional cooperation of the TOM complex and the presequence translocase of the inner membrane. We conclude that mitochondria employ different mechanisms for translocation of multispanning proteins across the aqueous intermembrane space.

Electron Transport Complex IV↗
PubMed1990

Bacterial killing and inhibition of inner membrane activity by C5b-9 complexes as a function of the sequential addition of C9 to C5b-8 sites.

The assembly of the C5b-9 complex on the outer membrane of C-sensitive cells of Escherichia coli results in a rapid inhibition of inner membrane function and ultimately a loss of cell viability. Cells bearing C5b-8 sites suffer no deleterious effects; however, the addition of C9 results in a rapid inhibition of inner membrane function and cell death. An attempt was made to examine the relationship between the toxic effects of the C5b-9 complex and the number of C9 molecules per C5b-8 site. Cells bearing C5b-8 sites were exposed to excess C9 at 0 degrees C and washed three times at 4 degrees C. The number of C9 molecules bound to each cell was equivalent to the number of C5b-8 sites present on each cell, and no additional C9 molecules could be bound when the cells were maintained at 4 degrees C. These cells were then incubated at 37 degrees C for 3 min and returned to 0 degrees C, a technique which exposed additional C9-binding sites equivalent to the number of C9 molecules previously bound to the cells. This technique was repeated and demonstrated that the sequential build-up of a C5b-9 site with two C9 molecules per C5b-8 site was capable of inhibiting both inner membrane function (respiration and amino acid transport) and cell viability. Three C9 molecules per complex had effects that approached the inhibitory effects of complexes formed in the presence of excess C9.

Bacterial Physiological Phenomena↗
PubMed2006

The Tim21 binding domain connects the preprotein translocases of both mitochondrial membranes.

Proteins destined for the mitochondrial matrix are imported by the translocase of the outer membrane--the TOM complex--and the presequence translocase of the inner membrane--the TIM23 complex. At present, there is no structural information on components of the presequence translocase. Tim21, a subunit of the presequence translocase consisting of a membrane anchor and a carboxy-terminal domain exposed to the intermembrane space, directly connects the TOM and TIM23 complexes by binding to the intermembrane space domain of the Tom22 receptor. We crystallized the binding domain of Tim21 of Saccharomyces cerevisiae and determined its structure at 1.6 A resolution. The Tim21 structure represents a new alpha/beta-mixed protein fold with two alpha-helices flanked by an extended eight-stranded beta-sheet. We also identified a core sequence of Tom22 that binds to Tim21. Furthermore, negatively charged amino-acid residues of Tom22 are important for binding to Tim21. Here we suggest a mechanism for the TOM-TIM interaction.

Amino Acid Sequence↗
PubMed2006

Outer membrane active transport: structure of the BtuB:TonB complex.

In Gram-negative bacteria, the import of essential micronutrients across the outer membrane requires a transporter, an electrochemical gradient of protons across the inner membrane, and an inner membrane protein complex (ExbB, ExbD, TonB) that couples the proton-motive force to the outer membrane transporter. The inner membrane protein TonB binds directly to a conserved region, called the Ton-box, of the transporter. We solved the structure of the cobalamin transporter BtuB in complex with the C-terminal domain of TonB. In contrast to its conformations in the absence of TonB, the Ton-box forms a beta strand that is recruited to the existing beta sheet of TonB, which is consistent with a mechanical pulling model of transport.

Bacterial Outer Membrane Proteins↗