scholarly journals Protein Import into Hydrogenosomes of Trichomonas vaginalis Involves both N-Terminal and Internal Targeting Signals: a Case Study of Thioredoxin Reductases

2008 ◽  
Vol 7 (10) ◽  
pp. 1750-1757 ◽  
Author(s):  
Marek Mentel ◽  
Verena Zimorski ◽  
Patrick Haferkamp ◽  
William Martin ◽  
Katrin Henze
Keyword(s):  
Trichomonas Vaginalis ◽  
Protein Import ◽  
Atp Synthesis ◽  
Antioxidant Systems ◽  
Low Oxygen ◽  
Oxygen Sensitive ◽  
Targeting Signal ◽  
Targeting Signals ◽  
Thioredoxin Reductases

ABSTRACT The parabasalian flagellate Trichomonas vaginalis harbors mitochondrion-related and H2-producing organelles of anaerobic ATP synthesis, called hydrogenosomes, which harbor oxygen-sensitive enzymes essential to its pyruvate metabolism. In the human urogenital tract, however, T. vaginalis is regularly exposed to low oxygen concentrations and therefore must possess antioxidant systems protecting the organellar environment against the detrimental effects of molecular oxygen and reactive oxygen species. We have identified two closely related hydrogenosomal thioredoxin reductases (TrxRs), the hitherto-missing component of a thioredoxin-linked hydrogenosomal antioxidant system. One of the two hydrogenosomal TrxR isoforms, TrxRh1, carried an N-terminal extension resembling known hydrogenosomal targeting signals. Expression of hemagglutinin-tagged TrxRh1 in transfected T. vaginalis cells revealed that its N-terminal extension was necessary to import the protein into the organelles. The second hydrogenosomal TrxR isoform, TrxRh2, had no N-terminal targeting signal but was nonetheless efficiently targeted to hydrogenosomes. N-terminal presequences from hydrogenosomal proteins with known processing sites, i.e., the alpha subunit of succinyl coenzyme A synthetase (SCSα) and pyruvate:ferredoxin oxidoreductase A, were investigated for their ability to direct mature TrxRh1 to hydrogenosomes. Neither presequence directed TrxRh1 to hydrogenosomes, indicating that neither extension is, by itself, sufficient for hydrogenosomal targeting. Moreover, SCSα lacking its N-terminal extension was efficiently imported into hydrogenosomes, indicating that this extension is not required for import of this major hydrogenosomal protein. The finding that some hydrogenosomal enzymes require N-terminal signals for import but that in others the N-terminal extension is not necessary for targeting indicates the presence of additional targeting signals within the mature subunits of several hydrogenosome-localized proteins.

scholarly journals Amino-terminal extension generated from an upstream AUG codon increases the efficiency of mitochondrial import of yeast N2,N2-dimethylguanosine-specific tRNA methyltransferases.

1989 ◽  
Vol 9 (4) ◽  
pp. 1611-1620 ◽  
Author(s):  
S R Ellis ◽  
A K Hopper ◽  
N C Martin
Keyword(s):  
Protein Import ◽  
Amino Terminus ◽  
Mitochondrial Targeting ◽  
Amino Terminal ◽  
Trna Methyltransferase ◽  
Targeting Signal ◽  
Targeting Signals ◽  
Passenger Protein

Fusions between the TRM1 gene of Saccharomyces cerevisiae and COXIV or DHFR were made to examine the mitochondrial targeting signals of N2,N2-dimethylguanosine-specific tRNA methyltransferase [tRNA (m2(2)G)dimethyltransferase]. This enzyme is responsible for the modification of both mitochondrial and cytoplasmic tRNAs. We have previously shown that two forms of the enzyme are translated from two in-frame ATGs in this gene, that they differ by a 16-amino-acid amino-terminal extension, and that both the long and short forms are imported into mitochondria. Results of studies to test the ability of various TRM1 sequences to serve as surrogate mitochondrial targeting signals for passenger protein import in vitro and in vivo showed that the most efficient signal derived from tRNA (m2(2)G)dimethyltransferase included a combination of sequences from both the amino-terminal extension and the amino terminus of the shorter form of the enzyme. The amino-terminal extension itself did not serve as an independent mitochondrial targeting signal, whereas the amino terminus of the shorter form of tRNA (m2(2)G)dimethyltransferase did function in this regard, albeit inefficiently. We analyzed the first 48 amino acids of tRNA (m2(2)G)dimethyltransferase for elements of primary and secondary structure shared with other known mitochondrial targeting signals. The results lead us to propose that the most efficient signal spans the area around the second ATG of TRM1 and is consistent with the idea that there is a mitochondrial targeting signal present at the amino terminus of the shorter form of the enzyme and that the amino-terminal extension augments this signal by extending it to form a larger, more efficient mitochondrial targeting signal.

Amino-terminal extension generated from an upstream AUG codon increases the efficiency of mitochondrial import of yeast N2,N2-dimethylguanosine-specific tRNA methyltransferases

1989 ◽  
Vol 9 (4) ◽  
pp. 1611-1620
Author(s):  
S R Ellis ◽  
A K Hopper ◽  
N C Martin
Keyword(s):  
Protein Import ◽  
Amino Terminus ◽  
Mitochondrial Targeting ◽  
Amino Terminal ◽  
Trna Methyltransferase ◽  
Targeting Signal ◽  
Targeting Signals ◽  
Passenger Protein

Fusions between the TRM1 gene of Saccharomyces cerevisiae and COXIV or DHFR were made to examine the mitochondrial targeting signals of N2,N2-dimethylguanosine-specific tRNA methyltransferase [tRNA (m2(2)G)dimethyltransferase]. This enzyme is responsible for the modification of both mitochondrial and cytoplasmic tRNAs. We have previously shown that two forms of the enzyme are translated from two in-frame ATGs in this gene, that they differ by a 16-amino-acid amino-terminal extension, and that both the long and short forms are imported into mitochondria. Results of studies to test the ability of various TRM1 sequences to serve as surrogate mitochondrial targeting signals for passenger protein import in vitro and in vivo showed that the most efficient signal derived from tRNA (m2(2)G)dimethyltransferase included a combination of sequences from both the amino-terminal extension and the amino terminus of the shorter form of the enzyme. The amino-terminal extension itself did not serve as an independent mitochondrial targeting signal, whereas the amino terminus of the shorter form of tRNA (m2(2)G)dimethyltransferase did function in this regard, albeit inefficiently. We analyzed the first 48 amino acids of tRNA (m2(2)G)dimethyltransferase for elements of primary and secondary structure shared with other known mitochondrial targeting signals. The results lead us to propose that the most efficient signal spans the area around the second ATG of TRM1 and is consistent with the idea that there is a mitochondrial targeting signal present at the amino terminus of the shorter form of the enzyme and that the amino-terminal extension augments this signal by extending it to form a larger, more efficient mitochondrial targeting signal.

scholarly journals Peroxisome Senescence in Human Fibroblasts

2002 ◽  
Vol 13 (12) ◽  
pp. 4243-4255 ◽  
Author(s):  
Julie E. Legakis ◽  
Jay I. Koepke ◽  
Chris Jedeszko ◽  
Ferdous Barlaskar ◽  
Laura J. Terlecky ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Protein Import ◽  
Human Fibroblasts ◽  
Toxic Metabolite ◽  
Age Related ◽  
Peroxisomal Targeting ◽  
Targeting Signal ◽  
Effects Of Aging ◽  
Antioxidant Enzyme Catalase ◽  
Import Receptor

The molecular mechanisms of peroxisome biogenesis have begun to emerge; in contrast, relatively little is known about how the organelle functions as cells age. In this report, we characterize age-related changes in peroxisomes of human cells. We show that aging compromises peroxisomal targeting signal 1 (PTS1) protein import, affecting in particular the critical antioxidant enzyme catalase. The number and appearance of peroxisomes are altered in these cells, and the organelles accumulate the PTS1-import receptor, Pex5p, on their membranes. Concomitantly, cells produce increasing amounts of the toxic metabolite hydrogen peroxide, and we present evidence that this increased load of reactive oxygen species may further reduce peroxisomal protein import and exacerbate the effects of aging.

scholarly journals Characterization of Mmp37p, aSaccharomyces cerevisiaeMitochondrial Matrix Protein with a Role in Mitochondrial Protein Import

2006 ◽  
Vol 17 (9) ◽  
pp. 4051-4062 ◽  
Author(s):  
Michelle R. Gallas ◽  
Mary K. Dienhart ◽  
Rosemary A. Stuart ◽  
Roy M. Long
Keyword(s):  
Matrix Protein ◽  
Protein Import ◽  
Mitochondrial Protein ◽  
Temperature Sensitive ◽  
Inner Membrane ◽  
Mitochondrial Inner Membrane ◽  
Close Proximity ◽  
The Matrix ◽  
Targeting Signal

Many mitochondrial proteins are encoded by nuclear genes and after translation in the cytoplasm are imported via translocases in the outer and inner membranes, the TOM and TIM complexes, respectively. Here, we report the characterization of the mitochondrial protein, Mmp37p (YGR046w) and demonstrate its involvement in the process of protein import into mitochondria. Haploid cells deleted of MMP37 are viable but display a temperature-sensitive growth phenotype and are inviable in the absence of mitochondrial DNA. Mmp37p is located in the mitochondrial matrix where it is peripherally associated with the inner membrane. We show that Mmp37p has a role in the translocation of proteins across the mitochondrial inner membrane via the TIM23-PAM complex and further demonstrate that substrates containing a tightly folded domain in close proximity to their mitochondrial targeting sequences display a particular dependency on Mmp37p for mitochondrial import. Prior unfolding of the preprotein, or extension of the region between the targeting signal and the tightly folded domain, relieves their dependency for Mmp37p. Furthermore, evidence is presented to show that Mmp37 may affect the assembly state of the TIM23 complex. On the basis of these findings, we hypothesize that the presence of Mmp37p enhances the early stages of the TIM23 matrix import pathway to ensure engagement of incoming preproteins with the mtHsp70p/PAM complex, a step that is necessary to drive the unfolding and complete translocation of the preprotein into the matrix.

scholarly journals Presence of a Member of the Mitochondrial Carrier Family in Hydrogenosomes: Conservation of Membrane-Targeting Pathways between Hydrogenosomes and Mitochondria

2000 ◽  
Vol 20 (7) ◽  
pp. 2488-2497 ◽  
Author(s):  
Sabrina D. Dyall ◽  
Carla M. Koehler ◽  
Maria G. Delgadillo-Correa ◽  
Peter J. Bradley ◽  
Evelyn Plümper ◽  
...  
Keyword(s):  
Trichomonas Vaginalis ◽  
Protein Targeting ◽  
Phylogenetic Analyses ◽  
Eukaryotic Cell ◽  
Membrane Targeting ◽  
Carrier Proteins ◽  
Mitochondrial Carrier ◽  
Mitochondrial Carrier Family ◽  
Targeting Signal ◽  
Mitochondrial Carrier Proteins

ABSTRACT A number of microaerophilic eukaryotes lack mitochondria but possess another organelle involved in energy metabolism, the hydrogenosome. Limited phylogenetic analyses of nuclear genes support a common origin for these two organelles. We have identified a protein of the mitochondrial carrier family in the hydrogenosome ofTrichomonas vaginalis and have shown that this protein, Hmp31, is phylogenetically related to the mitochondrial ADP-ATP carrier (AAC). We demonstrate that the hydrogenosomal AAC can be targeted to the inner membrane of mitochondria isolated from Saccharomyces cerevisiae through the Tim9-Tim10 import pathway used for the assembly of mitochondrial carrier proteins. Conversely, yeast mitochondrial AAC can be targeted into the membranes of hydrogenosomes. The hydrogenosomal AAC contains a cleavable, N-terminal presequence; however, this sequence is not necessary for targeting the protein to the organelle. These data indicate that the membrane-targeting signal(s) for hydrogenosomal AAC is internal, similar to that found for mitochondrial carrier proteins. Our findings indicate that the membrane carriers and membrane protein-targeting machinery of hydrogenosomes and mitochondria have a common evolutionary origin. Together, they provide strong evidence that a single endosymbiont evolved into a progenitor organelle in early eukaryotic cells that ultimately give rise to these two distinct organelles and support the hydrogen hypothesis for the origin of the eukaryotic cell.

Mechanism of protein import across the chloroplast envelope

2000 ◽  
Vol 28 (4) ◽  
pp. 485-491 ◽  
Author(s):  
K. Chen ◽  
X. Chen ◽  
D. J. Schnell
Keyword(s):  
Protein Import ◽  
Essential Elements ◽  
Chloroplast Envelope ◽  
Envelope Membrane ◽  
Outer Envelope ◽  
Double Membrane ◽  
Protein Subunits ◽  
Targeting Signals ◽  
Outer Envelope Membrane ◽  
Envelope Membranes

The development and maintenance of chloroplasts relies on the contribution of protein subunits from both plastid and nuclear genomes. Most chloroplast proteins are encoded by nuclear genes and are post-translationally imported into the organelle across the double membrane of the chloroplast envelope. Protein import into the chloroplast consists of two essential elements: the specific recognition of the targeting signals (transit sequences) of cytoplasmic preproteins by receptors at the outer envelope membrane and the subsequent translocation of preproteins simultaneously across the double membrane of the envelope. These processes are mediated via the co-ordinate action of protein translocon complexes in the outer (Toe apparatus) and inner (Tic apparatus) envelope membranes.

Metabolic control of peroxisome abundance

1999 ◽  
Vol 112 (10) ◽  
pp. 1579-1590 ◽  
Author(s):  
C.C. Chang ◽  
S. South ◽  
D. Warren ◽  
J. Jones ◽  
A.B. Moser ◽  
...  
Keyword(s):  
Metabolic Control ◽  
Matrix Protein ◽  
Protein Import ◽  
Zellweger Syndrome ◽  
Mutant Gene ◽  
Peroxisomal Membrane ◽  
Peroxisomal Targeting ◽  
Targeting Signal ◽  
Complementation Groups ◽  
Peroxisomal Targeting Signal

Zellweger syndrome and related disorders represent a group of lethal, genetically heterogeneous diseases. These peroxisome biogenesis disorders (PBDs) are characterized by defective peroxisomal matrix protein import and comprise at least 10 complementation groups. The genes defective in seven of these groups and more than 90% of PBD patients are now known. Here we examine the distribution of peroxisomal membrane proteins in fibroblasts from PBD patients representing the seven complementation groups for which the mutant gene is known. Peroxisomes were detected in all PBD cells, indicating that the ability to form a minimal peroxisomal structure is not blocked in these mutants. We also observed that peroxisome abundance was reduced fivefold in PBD cells that are defective in the PEX1, PEX5, PEX12, PEX6, PEX10, and PEX2 genes. These cell lines all display a defect in the import of proteins with the type-1 peroxisomal targeting signal (PTS1). In contrast, peroxisome abundance was unaffected in cells that are mutated in PEX7 and are defective only in the import of proteins with the type-2 peroxisomal targeting signal. Interestingly, a fivefold reduction in peroxisome abundance was also observed for cells lacking either of two PTS1-targeted peroxisomal beta-oxidation enzymes, acyl-CoA oxidase and 2-enoyl-CoA hydratase/D-3-hydroxyacyl-CoA dehydrogenase. These results indicate that reduced peroxisome abundance in PBD cells may be caused by their inability to import these PTS1-containing enzymes. Furthermore, the fact that peroxisome abundance is influenced by peroxisomal 105-oxidation activities suggests that there may be metabolic control of peroxisome abundance.

Protein import into orangelles: Hierarchical targeting signals

Cell ◽  
1986 ◽  
Vol 46 (3) ◽  
pp. 321-322 ◽  
Author(s):  
Alan Colman ◽  
Colin Robinson
Keyword(s):  
Protein Import ◽  
Targeting Signals
Sign in / Sign up

Export Citation Format

Share Document