scholarly journals Ribosome-binding Proteins Mdm38 and Mba1 Display Overlapping Functions for Regulation of Mitochondrial Translation

2010 ◽  
Vol 21 (12) ◽  
pp. 1937-1944 ◽  
Author(s):  
Heike Bauerschmitt ◽  
David U. Mick ◽  
Markus Deckers ◽  
Christine Vollmer ◽  
Soledad Funes ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Respiratory Chain ◽  
Membrane Insertion ◽  
Mitochondrial Translation ◽  
Respiratory Chain Complexes ◽  
Ribosome Binding ◽  
Chain Complexes ◽  
Inner Membrane Protein ◽  
Simultaneous Loss ◽  
Regulatory Functions

Biogenesis of respiratory chain complexes depends on the expression of mitochondrial-encoded subunits. Their synthesis occurs on membrane-associated ribosomes and is probably coupled to their membrane insertion. Defects in expression of mitochondrial translation products are among the major causes of mitochondrial disorders. Mdm38 is related to Letm1, a protein affected in Wolf-Hirschhorn syndrome patients. Like Mba1 and Oxa1, Mdm38 is an inner membrane protein that interacts with ribosomes and is involved in respiratory chain biogenesis. We find that simultaneous loss of Mba1 and Mdm38 causes severe synthetic defects in the biogenesis of cytochrome reductase and cytochrome oxidase. These defects are not due to a compromised membrane binding of ribosomes but the consequence of a mis-regulation in the synthesis of Cox1 and cytochrome b. Cox1 expression is restored by replacing Cox1-specific regulatory regions in the mRNA. We conclude, that Mdm38 and Mba1 exhibit overlapping regulatory functions in translation of selected mitochondrial mRNAs.

scholarly journals Mrpl36 Is Important for Generation of Assembly Competent Proteins during Mitochondrial Translation

2009 ◽  
Vol 20 (10) ◽  
pp. 2615-2625 ◽  
Author(s):  
Martin Prestele ◽  
Frank Vogel ◽  
Andreas S. Reichert ◽  
Johannes M. Herrmann ◽  
Martin Ott
Keyword(s):  
Protein Synthesis ◽  
Respiratory Chain ◽  
Large Subunit ◽  
Critical Role ◽  
Mitochondrial Translation ◽  
Respiratory Chain Complexes ◽  
Ribosomal Subunits ◽  
Terminal Domain ◽  
Chain Complexes ◽  
Mitochondrial Ribosome

The complexes of the respiratory chain represent mosaics of nuclear and mitochondrially encoded components. The processes by which synthesis and assembly of the various subunits are coordinated remain largely elusive. During evolution, many proteins of the mitochondrial ribosome acquired additional domains pointing at specific properties or functions of the translation machinery in mitochondria. Here, we analyzed the function of Mrpl36, a protein associated with the large subunit of the mitochondrial ribosome. This protein, homologous to the ribosomal protein L31 from bacteria, contains a mitochondria-specific C-terminal domain that is not required for protein synthesis per se; however, its absence decreases stability of Mrpl36. Cells lacking this C-terminal domain can still synthesize proteins, but these translation products fail to be properly assembled into respiratory chain complexes and are rapidly degraded. Surprisingly, overexpression of Mrpl36 seems to even increase the efficiency of mitochondrial translation. Our data suggest that Mrpl36 plays a critical role during translation that determines the rate of respiratory chain assembly. This important function seems to be carried out by a stabilizing activity of Mrpl36 on the interaction between large and small ribosomal subunits, which could influence accuracy of protein synthesis.

AML Cells Have Increased Mitochondrial Mass but Less Reserve in Their Respiratory Chain Complexes Leading to Heightened Sensitivity to Inhibition of Mitochondrial Protein Translation,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3585-3585
Author(s):  
Shrivani Sriskanthadevan ◽  
Skrtic Marko ◽  
Bozhena Livak ◽  
Yulia Jitkova ◽  
Rose Hurren ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Respiratory Chain ◽  
Mitochondrial Biogenesis ◽  
Complex Iii ◽  
Reserve Capacity ◽  
Mitochondrial Translation ◽  
Respiratory Chain Complexes ◽  
Mitochondrial Mass ◽  
Respiratory Complexes ◽  
Chain Complexes

Abstract Abstract 3585 Recent studies suggest that dysregulated mitochondrial oxygen consumption promotes the growth of AML cells. Therefore, we characterized the structure and metabolic function of the mitochondria in AML and normal G-CSF-mobilized hematopoietic mononuclear cells (PBSCs). Compared to PBSCs, 1o AML cells had increased mitochondrial mass as demonstrated by an increased mitochondrial DNA copy number and increased activity of matrix enzyme citrate synthase. The increased mitochondrial mass observed in 1o AML cells may represent larger mitochondria and/or more numerous mitochondria. Therefore, we evaluated the mitochondria of 1o AML and normal CD34+ hematopoietic cells by electron microscopy. The mitochondria in 1o AML cells were larger in area, but fewer in number compared to normal CD34+ cells. Mitochondria contain the respiratory chain complexes that promote oxidative phosphorylation. Given the dysregulated mitochondrial biogenesis in 1o AML cells, we examined the levels and capacity of the respiratory complexes in 1o AML and normal PBSCs. When normalized for mitochondrial mass, 1o AML cells (n = 12) had reduced activity of respiratory complexes III and IV compared to PBSCs (n = 10) (Mean complex III activity AML vs PBSC: 0.32 ± 0.04 RU vs 0.66 ± 0.11 RU p = 0.0063; Mean complex IV activity AML vs PBSC: 0.13 ± 0.01 RU vs 0.24 ± 0.02 RU, p= 0.0003). We evaluated the capacity of the respiratory complexes in AML cells and PBSCs by treating with increasing concentrations of the complex III inhibitor antimycin, and measuring the changes in oxygen consumption. AML cells displayed heightened sensitivity to the complex III inhibitor and less reserve capacity in the respiratory complex compared to PBSCs (mean concentration of antimycin required to reduce oxygen consumption by 50%: AML (n = 11) vs PBSC (n = 3): 13.7 ± 1.6 nM vs 29.0 ± 2.4 nM; p = 0.0007). AML cell lines were similar to 1o AML cells with decreased basal respiratory complex activity and reserve capacity compared to PBSCs. Given the reduced levels and reserve in the respiratory chain complexes in AML cells, we evaluated the effects of inhibiting mitochondrial protein translation in AML cells and PBSCs. Chemical (tigecycline, and chloramphenicol) and genetic (RNAi knockdown of the EF-Tu) inhibition of mitochondrial translation reduced the levels and function of the respiratory complexes that contain proteins encoded by mitochondrial DNA. Consistent with the reduced reserve capacity, inhibiting mitochondrial translation preferentially reduced oxygen consumption and viability of 1o AML cells and AML cell lines over PBSCs and normal CD34+ cells. To understand the molecular basis for the abnormal mitochondrial biogenesis in 1o AML cells, we measured levels of the NRF-1, TFAM and EF-Tu, genes known to positively regulate mitochondrial biogenesis. Compared to PBSCs, AML samples showed at least a 3-fold increase in mRNA expression of these genes. Myc is a positive regulator of NRF-1, TFAM and EF-Tu. Therefore, we measured levels of myc in 1o AML cells and PBSCs by Q-RT-PCR. Compared to PBSCs, myc was increased in 1o AML cells and positively correlated with expression of NRF-1, TFAM and EF-Tu as well as with mitochondrial mass. To determine whether increased myc expression is functionally related to the increased mitochondrial biogenesis and decreased reserve in respiratory capacity, we employed P493 Burkitt's cells with inducible myc knockdown. P493 cells expressing myc had increased mitochondrial mass, larger mitochondria, and increased basal oxygen consumption compared to the myc knockdown cells. When normalized for mitochondrial mass, myc expressing cells had reduced activity of respiratory complexes III and IV compared to myc knockdown cells. In addition, myc expressing cells had less reserve in respiratory complex III (concentration of antimycin required to reduce oxygen consumption by 50% –+ myc P493 vs –myc P493: 6.580 ± 0.393 nM vs 12.87 ± 1.97 nM p =0.0352). Thus, compared to normal hematopoietic cells, AML cells have greater mitochondrial mass but reduced reserve in their respiratory complexes. As a result of this decreased reserve, AML cells have a heightened sensitivity to inhibition of mitochondrial translation which reduces respiratory chain complex levels and activity. Genetically, the abnormal mitochondrial structure and function appears related to dysregulated myc and its influence on genes promoting increased mitochondrial biogenesis. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Taz1, an Outer Mitochondrial Membrane Protein, Affects Stability and Assembly of Inner Membrane Protein Complexes: Implications for Barth Syndrome

2005 ◽  
Vol 16 (11) ◽  
pp. 5202-5214 ◽  
Author(s):  
Katrin Brandner ◽  
David U. Mick ◽  
Ann E. Frazier ◽  
Rebecca D. Taylor ◽  
Chris Meisinger ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Respiratory Chain ◽  
Mitochondrial Membrane ◽  
Barth Syndrome ◽  
Outer Mitochondrial Membrane ◽  
Respiratory Chain Complexes ◽  
Complex Iv ◽  
Inner Membrane ◽  
Chain Complexes ◽  
Mitochondrial Membrane Protein

The Saccharomyces cerevisiae Taz1 protein is the orthologue of human Tafazzin, a protein that when inactive causes Barth Syndrome (BTHS), a severe inherited X-linked disease. Taz1 is a mitochondrial acyltransferase involved in the remodeling of cardiolipin. We show that Taz1 is an outer mitochondrial membrane protein exposed to the intermembrane space (IMS). Transport of Taz1 into mitochondria depends on the receptor Tom5 of the translocase of the outer membrane (TOM complex) and the small Tim proteins of the IMS, but is independent of the sorting and assembly complex (SAM). TAZ1 deletion in yeast leads to growth defects on nonfermentable carbon sources, indicative of a defect in respiration. Because cardiolipin has been proposed to stabilize supercomplexes of the respiratory chain complexes III and IV, we assess supercomplexes in taz1Δ mitochondria and show that these are destabilized in taz1Δ mitochondria. This leads to a selective release of a complex IV monomer from the III2IV2 supercomplex. In addition, assembly analyses of newly imported subunits into complex IV show that incorporation of the complex IV monomer into supercomplexes is affected in taz1Δ mitochondria. We conclude that inactivation of Taz1 affects both assembly and stability of respiratory chain complexes in the inner membrane of mitochondria.

scholarly journals Selective and Reversible Disruption of Mitochondrial Inner Membrane Protein Complexes by Lipophilic Cations

2021 ◽  
Author(s):  
Anezka Kafkova ◽  
Lisa Tilokani ◽  
Filip Trčka ◽  
Veronika Šrámková ◽  
Marie Vancová ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Respiratory Chain ◽  
Mitochondrial Membrane ◽  
Mitochondrial Morphology ◽  
Respiratory Chain Complexes ◽  
Inner Membrane ◽  
Protein Levels ◽  
Mitochondrial Inner Membrane ◽  
Chain Complexes ◽  
The Impact

ABSTRACTMitochondria represent an attractive drug target in the treatment of many diseases. One of the most commonly used approaches to deliver therapeutics specifically into mitochondria is their conjugation to the triphenylphosphonium (TPP) moiety. While the TPP molecule is often regarded as biologically inert, there is evidence that the moiety itself has a significant impact on the activity of mitochondrial respiratory chain complexes.We studied the impact of a subchronic exposure of C2C12 mouse myoblasts to a set of TPP derivatives. Our results show that the alkyl-TPP cause dose- and hydrophobicity-dependent alterations of mitochondrial morphology and a selective decrease in the amounts of mitochondrial inner membrane (but not outer membrane) proteins including structural subunits of the respiratory chain complexes (such as MT-CO1 of complex IV or NDUFB8 of complex I), as well as components of the mitochondrial calcium uniporter complex (MCUC). The treatment with alkyl-TPP additionally resulted in OPA1-cleavage. Both the structural and functional effects of alkyl-TPP were found to be reversible. A similar effect was observed with the mitochondria-targeted antioxidant MitoQ. We further show that this effect on protein levels cannot be explained solely by a decrease in mitochondrial membrane potential.We conclude that TPP derivatives negatively affect mitochondrial structure and function at least in part through their effect on selective mitochondrial membrane protein levels via a reversible controlled process.

scholarly journals Assembly factors monitor sequential hemylation of cytochrome b to regulate mitochondrial translation

2014 ◽  
Vol 205 (4) ◽  
pp. 511-524 ◽  
Author(s):  
Markus Hildenbeutel ◽  
Eric L. Hegg ◽  
Katharina Stephan ◽  
Steffi Gruschke ◽  
Brigitte Meunier ◽  
...  
Keyword(s):  
Electron Transport ◽  
Cytochrome B ◽  
Mitochondrial Respiratory Chain ◽  
Complex Iii ◽  
Mitochondrial Translation ◽  
Respiratory Chain Complexes ◽  
Mitochondrial Inner Membrane ◽  
Sequence Of Events ◽  
Chain Complexes ◽  
Assembly Factors

Mitochondrial respiratory chain complexes convert chemical energy into a membrane potential by connecting electron transport with charge separation. Electron transport relies on redox cofactors that occupy strategic positions in the complexes. How these redox cofactors are assembled into the complexes is not known. Cytochrome b, a central catalytic subunit of complex III, contains two heme bs. Here, we unravel the sequence of events in the mitochondrial inner membrane by which cytochrome b is hemylated. Heme incorporation occurs in a strict sequential process that involves interactions of the newly synthesized cytochrome b with assembly factors and structural complex III subunits. These interactions are functionally connected to cofactor acquisition that triggers the progression of cytochrome b through successive assembly intermediates. Failure to hemylate cytochrome b sequesters the Cbp3–Cbp6 complex in early assembly intermediates, thereby causing a reduction in cytochrome b synthesis via a feedback loop that senses hemylation of cytochrome b.

Relationships between the activity of respiratory-chain complexes in pre- (biopsy) or post-slaughter muscle samples and feed efficiency in random-bred Ghezel lambs

2017 ◽  
Vol 57 (8) ◽  
pp. 1674
Author(s):  
M. J. Zamiri ◽  
R. Mehrabi ◽  
G. R. Kavoosi ◽  
H. Rajaei Sharifabadi
Keyword(s):  
Respiratory Chain ◽  
Feed Intake ◽  
Enzyme Activities ◽  
Feed Efficiency ◽  
Average Daily Gain ◽  
Chain Complex ◽  
Respiratory Chain Complex ◽  
Respiratory Chain Complexes ◽  
Chain Complexes ◽  
Daily Gain

The present study was conducted to determine the relationship between the activity of mitochondrial respiratory chain complexes in pre- and post-slaughter muscle samples and residual feed intake (RFI) in Ghezel male lambs born as a result of random mating. The study was based on the hypothesis that random-bred lambs with lower feed (or higher) RFI have lower (or higher) respiratory chain-complex activity in muscle samples. Lambs (n = 30) were fed a diet consisting of 70% concentrate and 30% alfalfa hay during a 70-day period. Individual feed intake and average daily gain were recorded to calculate the RFI, feed-conversion ratio (FCR) and adjusted FCR (aFCR). On the basis of these calculations, the lambs were classified into low and high groups for RFI, with FCR and aFCR (n = 22) being one standard deviation above or below the means; this was corroborated by Student’s t-test (P < 0.01). At the end of the experiment, a 10-g biopsy sample was taken from the posterior side of the left femoral biceps. After 24 h, the lambs were slaughtered, and a sample from the posterior side of the right femoral biceps was dissected for determination of mitochondrial protein and respiratory chain-complex activities (Complexes I–V). The RFI was not correlated with the metabolic bodyweight and average daily gain, but was positively correlated (r = 0.56) with the average daily feed intake (P < 0.01); mean daily feed intake in the low-RFI group was 200 g less than that in the high-RFI group. The FCR and aFCR were not significantly (P > 0.05) correlated with average daily feed intake (r = 0.39 and r = 0.36 respectively), but showed a negative correlation (P < 0.01) with average daily gain (r = –0.73 and r = –0.76 respectively). Although very high negative correlations were recorded between the activities of all five respiratory-chain complexes and RFI in muscle samples obtained before (–0.91 to –0.97) and after (–0.92 to –0.97) slaughter, Complexes I and V showed small negative correlations (–0.40) with FCR or aFCR (P < 0.05). Enzyme activities of the respiratory-chain Complexes I, III and V were not significantly different between the pre- and post-slaughter biopsy samples; however, the enzyme activities of respiratory-chain Complexes II and IV were slightly higher in post-slaughter samples (P < 0.01). These results suggested that it may be possible to use the enzymatic activity of respiratory-chain complexes in muscle biopsy samples for screening of lambs for RFI, providing a useful procedure for genetic selection of lambs for this component of feed efficiency. These encouraging results need to be verified in further experiments using other sheep breeds and a larger number of lambs.

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