Impact of the Mitochondrial Genetic Background in Complex III Deficiency

BACKGROUND: In recent years clinical evidence has emphasized the importance of the mtDNA genetic background that hosts a primary pathogenic mutation in the clinical expression of mitochondrial disorders, but little experimental confirmation has been provided. We have analyzed the pathogenic role of a novel homoplasmic mutation (m.15533 A>G) in the cytochrome b (MT-CYB) gene in a patient presenting with lactic acidosis, seizures, mild mental delay, and behaviour abnormalities. METHODOLOGY: Spectrophotometric analyses of the respiratory chain enzyme activities were performed in different tissues, the whole muscle mitochondrial DNA of the patient was sequenced, and the novel mutation was confirmed by PCR-RFLP. Transmitochondrial cybrids were constructed to confirm the pathogenicity of the mutation, and assembly/stability studies were carried out in fibroblasts and cybrids by means of mitochondrial translation inhibition in combination with blue native gel electrophoresis. PRINCIPAL FINDINGS: Biochemical analyses revealed a decrease in respiratory chain complex III activity in patient's skeletal muscle, and a combined enzyme defect of complexes III and IV in fibroblasts. Mutant transmitochondrial cybrids restored normal enzyme activities and steady-state protein levels, the mutation was mildly conserved along evolution, and the proband's mother and maternal aunt, both clinically unaffected, also harboured the homoplasmic mutation. These data suggested a nuclear genetic origin of the disease. However, by forcing the de novo functioning of the OXPHOS system, a severe delay in the biogenesis of the respiratory chain complexes was observed in the mutants, which demonstrated a direct functional effect of the mitochondrial genetic background. CONCLUSIONS: Our results point to possible pitfalls in the detection of pathogenic mitochondrial mutations, and highlight the role of the genetic mtDNA background in the development of mitochondrial disorders

Periodic trends and easy estimation of relative stabilities in 11-vertex nido-p-block-heteroboranes and -borates

Density functional theory computations were carried out for 11-vertex nido-p-block-hetero(carba)boranes and -borates containing silicon, germanium, tin, arsenic, antimony, sulfur, selenium and tellurium heteroatoms. A set of quantitative values called “estimated energy penalties” was derived by comparing the energies of two reference structures that differ with respect to one structural feature only. These energy penalties behave additively, i.e., they allow us to reproduce the DFT-computed relative stabilities of 11-vertex nido-heteroboranes in general with good accuracy and to predict the thermodynamic stabilities of unknown structures easily. Energy penalties for neighboring heteroatoms (HetHet and HetHet′) decrease down the group and increase along the period (indirectly proportional to covalent radii). Energy penalties for a five- rather than four-coordinate heteroatom, [Het5k(1) and Het5k(2)], generally, increase down group 14 but decrease down group 16, while there are mixed trends for group 15 heteroatoms. The sum of HetHet′ energy penalties results in different but easily predictable open-face heteroatom positions in the thermodynamically most stable mixed heterocarbaboranes and -borates with more than two heteroatoms

Multinuclear NMR characterisation of the complexes between chiral 3-aminopyrrolidine lithium amides and n-butyllithium

From a set of one- and two-dimensional 1H, 13C and 6Li NMR experiments, we propose the formation of a well organised 1:1 tight complex between substituted 3-aminopyrrolidine lithium amides and n-butyllithium. This complex is probably at the origin of the stereoselection observed in the asymmetric condensation of n-butyllithium onto aromatic aldehydes

Mitochondrial Respiratory Supercomplexes in Physiology and Diseases

In eukaryotic cells, mitochondria play the fundamental role of ATP production during the process of oxidative phosphorylation (OXPHOS). However, these cytosolic organelles also have several other important physiological functions, including sugar and fatty acid catabo- lism, amino acid metabolism, buffering of the cytosolic calcium concentration (Rizzuto et\ua0al., 2012), regulation and execution of different types of cell death (Galluzzi et\ua0al., 2012) and arrangement of adaptive responses to perturbations of intracellular homeostasis (Liesa and Shirihai, 2013). Furthermore, mitochondria are able to discharge a range of intracel- lular signals including reactive oxygen species (ROS), mitochondrial DNA (mtDNA) and specific proteins, thus operating as fundamental hubs of a wide array of signalling pathways (Galluzzi et\ua0al., 2012)