Thermal performance of the electron transport system Complex III in seven Alabama fishes.

Management of fish populations for conservation in thermally variable systems requires an understanding of the fish's underlying physiology and responses to thermal stress. Physiological research at the organismal level provides information on the overall effects of stressors such as extreme temperature fluctuations. While experiments with whole organisms provide information as to the overall effects of temperature fluctuations, biochemical assays of thermal stress provide direct results of exposure that are both sensitive and specific. Electron transport system (ETS; Complex III) assays quantify a rate-limiting step of respiratory enzymes. Parameters that can be estimated via this approach include optimum thermal temperature (Topt ) and optimal breadth of thermal performance (Tbreadth ), which can both be related to organismal-level temperature thresholds. We exposed enzymes of seven fish species (native fish chosen to represent a typical community in Alabama streams) to temperatures in the range 11-44°C. The resultant enzymatic thermal performance curves showed that Topt , the lower temperature for enzyme optimal thermal performance (Tlow ), the upper temperature for enzyme optimal thermal performance (Tup ), and Tbreadth differed among species. Relationships between enzymatic activity and temperature for all fish followed a pattern of steadily increasing enzyme activity to Topt before gradually decreasing with increasing temperature. A comparison of our enzyme optimum and upper-temperature limit results versus published critical thermal maxima values supports that ETS Complex III assays may be useful for assessing organismal-level thermal tolerance.

Structure of a functional obligate complex III2IV2 respiratory supercomplex from Mycobacterium smegmatis.

In the mycobacterial electron-transport chain, respiratory complex III passes electrons from menaquinol to complex IV, which in turn reduces oxygen, the terminal acceptor. Electron transfer is coupled to transmembrane proton translocation, thus establishing the electrochemical proton gradient that drives ATP synthesis. We isolated, biochemically characterized, and determined the structure of the obligate III2IV2 supercomplex from Mycobacterium smegmatis, a model for Mycobacterium tuberculosis. The supercomplex has quinol:O2 oxidoreductase activity without exogenous cytochrome c and includes a superoxide dismutase subunit that may detoxify reactive oxygen species produced during respiration. We found menaquinone bound in both the Qo and Qi sites of complex III. The complex III-intrinsic diheme cytochrome cc subunit, which functionally replaces both cytochrome c1 and soluble cytochrome c in canonical electron-transport chains, displays two conformations: one in which it provides a direct electronic link to complex IV and another in which it serves as an electrical switch interrupting the connection.

Examination of the superoxide/hydrogen peroxide forming and quenching potential of mouse liver mitochondria.

Pyruvate dehydrogenase (PDHC) and α-ketoglutarate dehydrogenase complex (KGDHC) are important sources of reactive oxygen species (ROS). In addition, it has been found that mitochondria can also serve as sinks for cellular hydrogen peroxide (H2O2). However, the ROS forming and quenching capacity of liver mitochondria has never been thoroughly examined. Here, we show that mouse liver mitochondria use catalase, glutathione (GSH), and peroxiredoxin (PRX) systems to quench ROS. Incubation of mitochondria with catalase inhibitor 3-amino-1,2,4-triazole (triazole) induced a significant increase in pyruvate or α-ketoglutarate driven O2-/H2O2 formation. 1-Choro-2,4-dinitrobenzene (CDNB), which depletes glutathione (GSH), elicited a similar effect. Auranofin (AF), a thioredoxin reductase-2 (TR2) inhibitor which disables the PRX system, did not significantly change O2-/H2O2 formation. By contrast catalase, GSH, and PRX were all required to scavenging extramitochondrial H2O2. In this study, the ROS forming potential of PDHC, KGDHC, Complex I, and Complex III was also profiled. Titration of mitochondria with 3-methyl-2-oxovaleric acid (KMV), a specific inhibitor for O2-/H2O2 production by KGDHC, induced a ~86% and ~84% decrease in ROS production during α-ketoglutarate and pyruvate oxidation. Titration of myxothiazol, a Complex III inhibitor, decreased O2-/H2O2 formation by ~45%. Rotenone also lowered ROS production in mitochondria metabolizing pyruvate or α-ketoglutarate indicating that Complex I does not contribute to ROS production during forward electron transfer from NADH. Taken together, our results indicate that KGDHC and Complex III are high capacity sites for O2-/H2O2 production in mouse liver mitochondria. We also confirm that catalase plays a role in quenching either exogenous or intramitochondrial H2O2.

Tether mutations that restore function and suppress pleiotropic phenotypes of the C. elegans isp-1(qm150) Rieske iron-sulfur protein.

Mitochondria play an important role in numerous diseases as well as normative aging. Severe reduction in mitochondrial function contributes to childhood disorders such as Leigh Syndrome, whereas mild disruption can extend the lifespan of model organisms. The Caenorhabditis elegans isp-1 gene encodes the Rieske iron-sulfur protein subunit of cytochrome c oxidoreductase (complex III of the electron transport chain). The partial loss of function allele, isp-1(qm150), leads to several pleiotropic phenotypes. To better understand the molecular mechanisms of ISP-1 function, we sought to identify genetic suppressors of the delayed development of isp-1(qm150) animals. Here we report a series of intragenic suppressors, all located within a highly conserved six amino acid tether region of ISP-1. These intragenic mutations suppress all of the evaluated isp-1(qm150) phenotypes, including developmental rate, pharyngeal pumping rate, brood size, body movement, activation of the mitochondrial unfolded protein response reporter, CO2 production, mitochondrial oxidative phosphorylation, and lifespan extension. Furthermore, analogous mutations show a similar effect when engineered into the budding yeast Rieske iron-sulfur protein Rip1, revealing remarkable conservation of the structure-function relationship of these residues across highly divergent species. The focus on a single subunit as causal both in generation and in suppression of diverse pleiotropic phenotypes points to a common underlying molecular mechanism, for which we propose a "spring-loaded" model. These observations provide insights into how gating and control processes influence the function of ISP-1 in mediating pleiotropic phenotypes including developmental rate, movement, sensitivity to stress, and longevity.

TAF-4 is required for the life extension of isp-1, clk-1 and tpk-1 Mit mutants.

While numerous life-extending manipulations have been discovered in the nematode Caenorhabditis elegans, one that remains most enigmatic is disruption of oxidative phosphorylation. In order to unravel how such an ostensibly deleterious manipulation can extend lifespan, we sought to identify the ensemble of nuclear transcription factors that are activated in response to defective mitochondrial electron transport chain (ETC) function. Using a feeding RNAi approach, we targeted over 400 transcription factors and identified 15 that, when reduced in function, reproducibly and differentially altered the development, stress response, and/or fecundity of isp-1(qm150) Mit mutants relative to wild-type animals. Seven of these transcription factors--AHA-1, CEH-18, HIF-1, JUN-1, NHR-27, NHR-49 and the CREB homolog-1 (CRH-1)-interacting protein TAF-4--were also essential for isp-1 life extension. When we tested the involvement of these seven transcription factors in the life extension of two other Mit mutants, namely clk-1(qm30) and tpk-1(qm162), TAF-4 and HIF-1 were consistently required. Our findings suggest that the Mit phenotype is under the control of multiple transcriptional responses, and that TAF-4 and HIF-1 may be part of a general signaling axis that specifies Mit mutant life extension.

Atomistic simulations indicate cardiolipin to have an integral role in the structure of the cytochrome bc1 complex.

The reaction mechanism of the cytochrome (cyt) bc1 complex relies on proton and electron transfer to/from the substrate quinone/quinol, which in turn generate a proton gradient across the mitochondrial membrane. Cardiolipin (CL) have been suggested to play an important role in cyt bc1 function by both ensuring the structural integrity of the protein complex and also by taking part in the proton uptake. Yet, the atom-scale understanding of these highly charged four-tail lipids in the cyt bc1 function has remained quite unclear. We consider this issue through atomistic molecular dynamics simulations that are applied to the entire cyt bc1 dimer of the purple photosynthetic bacterium Rhodobacter capsulatus embedded in a lipid bilayer. We find CLs to spontaneously diffuse to the dimer interface to the immediate vicinity of the higher potential heme b groups of the complex's catalytic Qi-sites. This observation is in full agreement with crystallographic studies of the complex, and supports the view that CLs are key players in the proton uptake. The simulation results also allow us to present a refined picture for the dimer arrangement in the cyt bc1 complex, the novelty of our work being the description of the role of the surrounding lipid environment: in addition to the specific CL-protein interactions, we observe the protein domains on the positive side of the membrane to settle against the lipids. Altogether, the simulations discussed in this article provide novel views into the dynamics of cyt bc1 with lipids, complementing previous experimental findings.

Conversion of Corynebacterium glutamicum from an aerobic respiring to an aerobic fermenting bacterium by inactivation of the respiratory chain.

In this study a comparative analysis of three Corynebacterium glutamicum ATCC 13032 respiratory chain mutants lacking either the cytochrome bd branch (ΔcydAB), or the cytochrome bc1-aa3 branch (Δqcr), or both branches was performed. The lack of cytochrome bd oxidase was inhibitory only under conditions of oxygen limitation, whereas the absence of a functional cytochrome bc1-aa3 supercomplex led to decreases in growth rate, biomass yield, respiration and proton-motive force (pmf) and a strongly increased maintenance coefficient under oxygen excess. These results show that the bc1-aa3 supercomplex is of major importance for aerobic respiration. For the first time, a C. glutamicum strain with a completely inactivated aerobic respiratory chain was obtained (ΔcydABΔqcr), named DOOR (devoid of oxygen respiration), which was able to grow aerobically in BHI (brain-heart infusion) glucose complex medium with a 70% reduced biomass yield compared to the wild type. Surprisingly, reasonable aerobic growth was also possible in glucose minimal medium after supplementation with peptone. Under these conditions, the DOOR strain displayed a fermentative type of catabolism with l-lactate as major and acetate and succinate as minor products. The DOOR strain had about 2% of the oxygen consumption rate of the wild type, showing the absence of additional terminal oxidases. The pmf of the DOOR mutant was reduced by about 30% compared to the wild type. Candidates for pmf generation in the DOOR strain are succinate:menaquinone oxidoreductase, which probably can generate pmf in the direction of fumarate reduction, and F1FO-ATP synthase, which can couple ATP hydrolysis to the export of protons.

LYRM7/MZM1L is a UQCRFS1 chaperone involved in the last steps of mitochondrial Complex III assembly in human cells.

The mammalian Complex III (CIII) assembly process is yet to be completely understood. There is still a lack in understanding of how the structural subunits are put together and which additional factors are involved. Here we describe the identification and characterization of LYRM7, a human protein displaying high sequence homology to the Saccharomyces cerevisiae protein Mzm1, which was recently shown as an assembly factor for Rieske Fe-S protein incorporation into the yeast cytochrome bc(1) complex. We conclude that human LYRM7, which we propose to be renamed MZM1L (MZM1-like), works as a human Rieske Fe-S protein (UQCRFS1) chaperone, binding to this subunit within the mitochondrial matrix and stabilizing it prior to its translocation and insertion into the late CIII dimeric intermediate within the mitochondrial inner membrane. Thus, LYRM7/MZM1L is a novel human CIII assembly factor involved in the UQCRFS1 insertion step, which enables formation of the mature and functional CIII enzyme.

Composition of the mitochondrial electron transport chain in acanthamoeba castellanii: structural and evolutionary insights.

The mitochondrion, derived in evolution from an α-proteobacterial progenitor, plays a key metabolic role in eukaryotes. Mitochondria house the electron transport chain (ETC) that couples oxidation of organic substrates and electron transfer to proton pumping and synthesis of ATP. The ETC comprises several multiprotein enzyme complexes, all of which have counterparts in bacteria. However, mitochondrial ETC assemblies from animals, plants and fungi are generally more complex than their bacterial counterparts, with a number of 'supernumerary' subunits appearing early in eukaryotic evolution. Little is known, however, about the ETC of unicellular eukaryotes (protists), which are key to understanding the evolution of mitochondria and the ETC. We present an analysis of the ETC proteome from Acanthamoeba castellanii, an ecologically, medically and evolutionarily important member of Amoebozoa (sister to Opisthokonta). Data obtained from tandem mass spectrometric (MS/MS) analyses of purified mitochondria as well as ETC complexes isolated via blue native polyacrylamide gel electrophoresis are combined with the results of bioinformatic queries of sequence databases. Our bioinformatic analyses have identified most of the ETC subunits found in other eukaryotes, confirming and extending previous observations. The assignment of proteins as ETC subunits by MS/MS provides important insights into the primary structures of ETC proteins and makes possible, through the use of sensitive profile-based similarity searches, the identification of novel constituents of the ETC along with the annotation of highly divergent but phylogenetically conserved ETC subunits.

Assembly factors of human mitochondrial respiratory chain complexes: physiology and pathophysiology.

Mitochondrial disorders are clinical syndromes associated with -abnormalities of the oxidative phosphorylation (OXPHOS) system, the main responsible for the production of energy in the cell. OXPHOS is carried out in the inner mitochondrial membrane by the five enzymatic complexes of the mitochondrial respiratory chain (MRC). The subunits constituting these multimeric complexes have a dual genetic origin, mitochondrial or nuclear. Hence, mitochondrial syndromes can be due to mutations of mitochondrial DNA or to abnormalities in nuclear genes. The biogenesis of the MRC complexes is an intricate and finely tuned process. The recent discovery of several OXPHOS-related human genes, mutated in different clinical syndromes, indicates that the majority of the inherited mitochondrial disorders are due to nuclear genes, and many of them encode proteins necessary for the proper assembly/stability of the MRC complexes. The detailed mechanisms of these processes are not fully understood and the exact function of many such factors remains obscure.We present an overview on the hypothesized assembly processes of the different MRC complexes, focusing on known assembly factors and their clinical importance.

Molecular mechanisms of superoxide production by the mitochondrial respiratory chain.

The mitochondrial respiratory chain is a major source of reactive oxygen species (ROS) in eukaryotic cells. Mitochondrial ROS production associated with a dysfunction of respiratory chain complexes has been implicated in a number of degenerative diseases and biological aging. Recent findings suggest that mitochondrial ROS can be integral components of cellular signal transduction as well. Within the respiratory chain, complexes I (NADH:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase; cytochrome bc (1) complex) are generally considered as the main producers of superoxide anions that are released into the mitochondrial matrix and the intermembrane space, respectively. The primary function of both respiratory chain complexes is to employ energy supplied by redox reactions to drive the vectorial transfer of protons into the mitochondrial intermembrane space. This process involves a set of distinct electron carriers designed to minimize the unwanted leak of electrons from reduced cofactors onto molecular oxygen and hence ROS generation under normal circumstances. Nevertheless, it seems plausible that superoxide is derived from intermediates of the normal catalytic cycles of complexes I and III. Therefore, a detailed understanding of the molecular mechanisms driving these enzymes is required to understand mitochondrial ROS production during oxidative stress and redox signalling. This review summarizes recent findings on the chemistry and control of the reactions within respiratory complexes I and III that result in increased superoxide generation. Regulatory contributions of other components of the respiratory chain, especially complex II (succinate:ubiquinone oxidoreductase) and the redox state of the ubiquinone pool (Q-pool) will be briefly discussed.

(-)-Epicatechin maintains endurance training adaptation in mice after 14 days of detraining.

The purpose of this study was to determine whether (-)-epicatechin (mainly found in cocoa) could attenuate detraining effects in the hindlimb muscles of mice. Thirty-two male mice were randomized into 4 groups: control, trained, trained with 14 d of detraining and vehicle (DT-14-W), and trained with 14 d of detraining and (-)-epicatechin [DT-14-(-)-Epi]. DT-14-(-)-Epi received (-)-epicatechin (1.0 mg/kg 2 ×/d), whereas water was given to the DT-14-W group. The latter 3 groups performed 5 wk of endurance training 5 ×/wk. Hindlimb muscles were harvested, and Western blots, as well as enzyme analyses, were performed. Training significantly increased capillary-to-fiber ratio (≈ 78.8%), cytochrome-c oxidase (≈ 35%), and activity (≈ 144%) compared to controls. These adaptations returned to control levels for the DT-14-W group, whereas the DT-14-(-)-Epi group was able to maintain capillary-to-fiber ratio (≈ 44%), CcO protein expression (≈ 45%), and activity (≈ 108%) above control levels. In addition, the increase in capillarity was related to decreased protein expression of thrombospondin-1, an antiangiogenic regulator. Furthermore, there were no significant differences in endurance capacity between the trained and DT-14-(-)-Epi groups. Our data suggest that (-)-epicatechin may be a suitable compound to maintain exercise-induced improved capillarity and mitochondrial capacity, even when exercise regimens are discontinued.

Biogenesis of the cytochrome bc(1) complex and role of assembly factors.

The cytochrome bc(1) complex is an essential component of the electron transport chain in most prokaryotes and in eukaryotic mitochondria. The catalytic subunits of the complex that are responsible for its redox functions are largely conserved across kingdoms. In eukarya, the bc(1) complex contains supernumerary subunits in addition to the catalytic core, and the biogenesis of the functional bc(1) complex occurs as a modular assembly pathway. Individual steps of this biogenesis have been recently investigated and are discussed in this review with an emphasis on the assembly of the bc(1) complex in the model eukaryote Saccharomyces cerevisiae. Additionally, a number of assembly factors have been recently identified. Their roles in bc(1) complex biogenesis are described, with special emphasis on the maturation and topogenesis of the yeast Rieske iron-sulfur protein and its role in completing the assembly of functional bc(1) complex. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.

Skeletal muscle electron transport chain dysfunction after sepsis in rats.

BACKGROUND: The derangement in oxygen utilization occurring during sepsis is likely to be linked to impaired mitochondrial functioning. Skeletal muscle comprises 50%-60% of body cell mass and represents the largest organ potentially affected by systemic inflammation. Thus, we investigated whether sepsis induced by cecal ligation and puncture (CLP) modifies mitochondrial activity in respiratory and nonrespiratory skeletal muscle. MATERIALS AND METHODS: Wistar rats were subjected to CLP and at different times, diaphragm and quadriceps were removed for the determination of electron transfer chain activities and mitochondrial oxidative stress. In addition, we determined diaphragm contractile strength. RESULTS: In the quadriceps, 12 h after CLP we demonstrated a significant diminution on complex II-III activity. At late times (48 h after CLP), we demonstrated a decrease in the activity of all electron transfer chain complexes, which seemed to be secondary to early oxidative stress and correlates with diaphragm contractile strength. Differently from diaphragm, electron transfer chain was not decreased after sepsis and even oxidative stress was not increased at all times tested. CONCLUSION: Our results suggest that quadriceps mitochondria are more resistant to sepsis-induced dysfunction.

2-amino-nonyl-6-methoxyl-tetralin muriate activity against Candida albicans augments endogenous reactive oxygen species production --a microarray analysis study.

Candida infections have become an increasingly significant problem, mainly because of the widespread nature of Candida and drug resistance. There is an urgent need to develop new classes of drugs for the treatment of opportunistic Candida infections, especially in medically complex patients. Previous studies have confirmed that 2-amino-nonyl-6-methoxyl-tetralin muriate (10b) possesses powerful antifungal activity in vitro against Candia albicans. To clarify the underlying action mechanism, an oligonucleotide microarray study was performed in C. albicans SC5314 without and with 10b treatment. The analytical results showed that energy metabolism-related genes, including glycolysis-related genes (PFK1, CDC19 and HXK2), fermentation-related genes (PDC11, ALD5 and ADH1) and respiratory electron transport chain-related genes (CBP3, COR1 and QCR8), were downregulated significantly. Functional analysis revealed that 10b treatment increased the generation of endogenous reactive oxygen species, and decreased mitochondrial membrane potential, ubiquinone-cytochrome c reductase (complex III) activity and intracellular ATP levels in C. albicans SC5314. Also, addition of the antioxidant ascorbic acid reduced the antifungal activity of 10b significantly. These results suggest that mitochondrial aerobic respiration shift and endogenous reactive oxygen species augmentation might contribute to the antifungal activity of 10b against C. albicans. This information may prove to be useful for the development of new strategies to treat Candida infections.

Primary role of mitochondrial Rieske iron-sulfur protein in hypoxic ROS production in pulmonary artery myocytes.

This study was designed to determine whether: (1) hypoxia could directly affect ROS production in isolated mitochondria and mitochondrial complex III from pulmonary artery smooth muscle cells (PASMCs) and (2) Rieske iron-sulfur protein in complex III might mediate hypoxic ROS production, leading to hypoxic pulmonary vasoconstriction (HPV). Our data, for the first time, demonstrate that hypoxia significantly enhances ROS production, measured by the standard ROS indicator dichlorodihydrofluorescein/diacetate, in isolated mitochondria from PASMCs. Studies using the newly developed, specific ROS biosensor pHyPer have found that hypoxia increases mitochondrial ROS generation in isolated PASMCs as well. Hypoxic ROS production has also been observed in isolated complex III. Rieske iron-sulfur protein silencing using siRNA abolishes the hypoxic ROS formation in isolated PASM complex III, mitochondria, and cells, whereas Rieske iron-sulfur protein overexpression produces the opposite effect. Rieske iron-sulfur protein silencing inhibits the hypoxic increase in [Ca(2+)](i) in PASMCs and hypoxic vasoconstriction in isolated PAs. These findings together provide novel evidence that mitochondria are the direct hypoxic targets in PASMCs, in which Rieske iron-sulfur protein in complex III may serve as an essential, primary molecule that mediates the hypoxic ROS generation, leading to an increase in intracellular Ca(2+) in PASMCs and HPV.

Increased mitochondrial matrix-directed superoxide production by fatty acid hydroperoxides in skeletal muscle mitochondria.

Previous studies have shown that muscle atrophy is associated with mitochondrial dysfunction and an increased rate of mitochondrial reactive oxygen species production. We recently demonstrated that fatty acid hydroperoxides (FA-OOHs) are significantly elevated in mitochondria isolated from atrophied muscles. The purpose of this study was to determine whether FA-OOHs can alter skeletal muscle mitochondrial function. We found that FA-OOHs (at low-micromolar concentrations) induce mitochondrial dysfunction assessed by a decrease in the rate of ATP production, oxygen consumption, and activity of respiratory chain complexes I and III. Using methods to distinguish superoxide release toward the matrix and toward the intermembrane space, we demonstrate that FA-OOHs significantly elevate oxidative stress in the mitochondrial matrix (and not the intermembrane space), with complex I as the major site of superoxide production (most probably from a site upstream of the ubiquinone binding site but downstream from the flavin binding site-the iron sulfur clusters). Our results are the first to indicate that FA-OOHs are important modulators of mitochondrial function and oxidative stress in skeletal muscle mitochondria and may play an important role in muscle atrophies that are associated with increased generation of FA-OOHs, e.g., denervation-induced muscle atrophy.

[The cytochrome bc1 complex in the mitochondrial respiratory chain functions according to the Q cycle hypothesis of Mitchell: the proof using a stochastic approach?]. / Le complexe bc1 de la chaîne respiratoire mitochondriale fonctionne selon l'hypothèse du cycle Q de Mitchell: la preuve par une approche stochastique?

The bc1 complex is a central complex in the mitochondrial respiratory chain. It links the electrons transfer from ubiquinol (or coenzyme Q) to cytochrome c and proton translocation across the inner mitochondrial membrane. It is widely agreed that the "Q-cycle mechanism" proposed by Mitchell correctly describes the bc1 complex working. It is based on an unexpected separation of the two electrons coming from the coenzyme Q bound at the Q0 site of the bc1 complex. Using the stochastic approach of Gillespie and the known spatial structure of bc1 complexes with the kinetic parameters described by Moser and Dutton we demonstrated the natural emergence of the Q-cycle mechanism and the quasi absence of short-circuits in the functional dimer of bc1 complex without the necessity to invoke any additional mechanism. This approach gives a framework which is well adapted to the modelling of all oxido-reduction reactions of the respiratory chain complexes, normal or mutant.

Molecular cloning, expression and characterization of bovine UQCC and its association with body measurement traits.

Ubiquinol-cytochrome c reductase complex chaperone (UQCC) involved in the development and maintenance of bone and cartilage is an important candidate gene for body measurement traits selection through marker-assisted selection (MAS). The expression of UQCC is upregulated in many human and animal models of height as well as other stature indexes. We have cloned the cDNA sequence coding UQCC gene in bovine. Genomic structural analysis indicated that bovine UQCC shares a high similarity with human UQCC. Furthermore, Real-Time PCR analysis show that the expression of bovine UQCC is remarkably different in diverse tissues, including high level expression in the spleen, heart and windpipe, and relatively low expression in other tissues. We also analyzed allele frequencies in different cattle breeds and an association study on the selected SNPs. SNP DraI A2691T in intron 1 and SNP Bsh1236I A3150G in intron 8 are significantly associated with Body Length (BL), Rump Length (RL), Chest Depth (CD) and Pin Bone Width (PBW). For the A2691T SNP marker, there are significant effects on the RL (p = 0.0001), CD (p = 0.0059) and PBW (p < 0.0001) in 679 individuals; with A3150G SNP marker, there are significant effects on the BL (p = 0.0047) and CD (p = 0.0454. Regarding association analysis of combination of the two SNPs, there are significant effects on the BL (p = 0.0215), CD (p = 0.0282) and PBW (p = 0.0329) in the total population. The results suggest that the UQCC gene is a candidate gene of body measurement traits in bovine reproduction and breeding, and provide data for establishing of an animal model using cattle to study big animal body type.

Mutation of the mitochondrial tyrosyl-tRNA synthetase gene, YARS2, causes myopathy, lactic acidosis, and sideroblastic anemia--MLASA syndrome.

Mitochondrial respiratory chain disorders are a heterogeneous group of disorders in which the underlying genetic defect is often unknown. We have identified a pathogenic mutation (c.156C>G [p.F52L]) in YARS2, located at chromosome 12p11.21, by using genome-wide SNP-based homozygosity analysis of a family with affected members displaying myopathy, lactic acidosis, and sideroblastic anemia (MLASA). We subsequently identified the same mutation in another unrelated MLASA patient. The YARS2 gene product, mitochondrial tyrosyl-tRNA synthetase (YARS2), was present at lower levels in skeletal muscle whereas fibroblasts were relatively normal. Complex I, III, and IV were dysfunctional as indicated by enzyme analysis, immunoblotting, and immunohistochemistry. A mitochondrial protein-synthesis assay showed reduced levels of respiratory chain subunits in myotubes generated from patient cell lines. A tRNA aminoacylation assay revealed that mutant YARS2 was still active; however, enzyme kinetics were abnormal compared to the wild-type protein. We propose that the reduced aminoacylation activity of mutant YARS2 enzyme leads to decreased mitochondrial protein synthesis, resulting in mitochondrial respiratory chain dysfunction. MLASA has previously been associated with PUS1 mutations; hence, the YARS2 mutation reported here is an alternative cause of MLASA.