Timing of dimerization of the bc1 complex during mitochondrial respiratory chain assembly.

The mitochondrial bc1 complex plays an important role in mitochondrial respiration. It transfers electrons from ubiquinol to the soluble electron shuttle cytochrome c and thereby contributes to the proton motive force across the inner mitochondrial membrane. In the yeast Saccharomyces cerevisiae, each monomer consists of three catalytic and seven accessory subunits. The bc1 complex is an obligate homo-dimer in all systems. It is currently not known when exactly during the assembly dimerization occurs. In this study, we determined that the dimer formation is an early event. Specifically, dimerization is mediated by the interaction of a stable tetramer formed by the two Cor subunits, Cor1 and Cor2, that joins assembly intermediate II, containing the fully hemylated cytochrome b and the two small accessory proteins, Qcr7 and Qcr8. Addition of cytochrome c1 and Qcr6 can either occur concomitantly or independently of dimerization. These results reveal a strict order in assembly, where dimerization occurs after stabilization of co-factor acquisition by cytochrome b. Finally, assembly is completed by addition of the remaining subunits.

The ribosome receptors Mrx15 and Mba1 jointly organize cotranslational insertion and protein biogenesis in mitochondria.

Mitochondrial gene expression in Saccharomyces cerevisiae is responsible for the production of highly hydrophobic subunits of the oxidative phosphorylation system. Membrane insertion occurs cotranslationally on membrane-bound mitochondrial ribosomes. Here, by employing a systematic mass spectrometry-based approach, we discovered the previously uncharacterized membrane protein Mrx15 that interacts via a soluble C-terminal domain with the large ribosomal subunit. Mrx15 contacts mitochondrial translation products during their synthesis and plays, together with the ribosome receptor Mba1, an overlapping role in cotranslational protein insertion. Taken together, our data reveal how these ribosome receptors organize membrane protein biogenesis in mitochondria.

The Posterior Parietal Cortex Subserves Precise Motor Timing in Professional Drummers.

The synchronization task is a well-established paradigm for the investigation of motor timing with respect to an external pacing signal. It requires subjects to synchronize their finger taps in synchrony with a regular metronome. A specific significance of the posterior parietal cortex (PPC) for superior synchronization in professional drummers has been suggested. In non-musicians, modulation of the excitability of the left PPC by means of transcranial direct current stimulation (tDCS) modulates synchronization performance of the right hand. In order to determine the significance of the left PPC for superior synchronization in drummers, we here investigate the effects of cathodal and anodal tDCS in 20 professional drummers on auditory-motor synchronization of the right hand. A continuation and a reaction time task served as control conditions. Moreover, the interaction between baseline performance and tDCS polarity was estimated in precise as compared to less precise synchronizers according to median split. Previously published data from 16 non-musicians were re-analyzed accordingly in order to highlight possible differences of tDCS effects in drummers and non-musicians. TDCS was applied for 10 min with an intensity of 0.25 mA over the left PPC. Behavioral measures were determined prior to and immediately after tDCS. In drummers the overall analysis of synchronization performance revealed significantly larger tap-to-tone asynchronies following anodal tDCS with the tap preceding the tone replicating findings in non-musicians. No significant effects were found on control tasks. The analysis for participants with large as compared to small baseline asynchronies revealed that only in drummers with small asynchronies tDCS interfered with synchronization performance. The re-analysis of the data from non-musicians indicated the reversed pattern. The data support the hypothesis that the PPC is involved in auditory-motor synchronization and extend previous findings by showing that its functional significance varies with musical expertise.

Spinal cord injury--incidence, prognosis, and outcome: an analysis of the TraumaRegister DGU.

BACKGROUND CONTEXT: Little is known about the incidence of spinal cord injury (SCI) in polytrauma patients. PURPOSE: The purpose of this study was to analyze incidence, prognosis, and outcome of SCI in polytrauma patients. STUDY DESIGN/SETTING: This is a retrospective multicenter cohort study. PATIENT SAMPLE: A total of 57,310 patients of TraumaRegister DGU (2002-2012) of the German Trauma Society were included. Aim of this large multicentre database is a standardized documentation of severely injured patients. OUTCOME MEASURES: Outcome measures were mortality and Glasgow Outcome 4Scale. METHODS: Inclusion criteria were adult blunt trauma patients (age greater than 16 years) and injury severity score (ISS) greater than 16. The severity of SCI was based on the Abbreviated Injury Scale (AIS), and the outcome of patients was assessed with the Glasgow Outcome Scale (GOS). Factors with an impact on the outcome were analyzed with a logistic regression model. RESULTS: Four thousand two hundred eighty five (7.5%) of 57,310 patients sustained SCI. Mean age was 48.9±20.7 years, ISS 28.0±12, and 72.7% were men. Two thousand two hundred twenty two (3.9%) SCIs involved the cervical, 1,388 (2.4%) the thoracic, and 791 (1.4%) the lumbar spine. One hundred fifty-nine (7.2%) cervical spine injuries were associated with transient neurologic deficit (TND) (AIS 3), 612 (27.5%) with an incomplete paraplegia (AIS 4), 1,101 (49.6%) with a complete paraplegia (AIS 5), and 350 (15.8%) with a complete lesion above C3 (AIS 6). Lesions of the thoracic spine showed in 93 (6.7%) of the 1,388 lesions a TND (AIS 3), in 332 (23.9%) an incomplete paraplegia (AIS 4), and in 963 (69.4%) a complete lesion (AIS 5). In the lumbar region, lesions were distributed as follows: TND (AIS 3) 145 (18.3%), incomplete paraplegia (AIS 4) 305 (38.6%), and complete lesion 341 (43.1%). Sepsis and multiorgan failure were found more often in patients with AIS 5/6 lesions (p<.001). The hospital length of stay in SCIs was significantly longer. Most of the patients (85.8%) with SCI were treated in Level I trauma centers. Spinal cord injuries had a minor impact in the mortality. Only AIS 6 injuries resulted in a significantly higher mortality (64.6%). Adjusted logistic regression analysis (target variable: GOS 4 or 5, good outcome) showed that the following factors were significantly associated with an unfavorable outcome (p≤.02): AIS greater than or equal to 4, age greater than or equal to 60 years, resuscitation, severe head injury, shock on scene, and severity of injury (ISS per point). CONCLUSIONS: Spinal cord injury with a neurologic deficit could be found in every 13th patient with polytrauma. Over half of the patients with SCI suffer from complete cord lesion. In polytrauma patients, SCI only has a limited influence on the mortality, with exception of AIS 6 lesions. Complications such as multiorgan failure or sepsis and extended hospital length of stay are more frequent in SCI.

A mutation in the human CBP4 ortholog UQCC3 impairs complex III assembly, activity and cytochrome b stability.

Complex III (cytochrome bc1) is a protein complex of the mitochondrial inner membrane that transfers electrons from ubiquinol to cytochrome c. Its assembly requires the coordinated expression of mitochondrial-encoded cytochrome b and nuclear-encoded subunits and assembly factors. Complex III deficiency is a severe multisystem disorder caused by mutations in subunit genes or assembly factors. Sequence-profile-based orthology predicts C11orf83, hereafter named UQCC3, to be the ortholog of the fungal complex III assembly factor CBP4. We describe a homozygous c.59T>A missense mutation in UQCC3 from a consanguineous patient diagnosed with isolated complex III deficiency, displaying lactic acidosis, hypoglycemia, hypotonia and delayed development without dysmorphic features. Patient fibroblasts have reduced complex III activity and lower levels of the holocomplex and its subunits than controls. They have no detectable UQCC3 protein and have lower levels of cytochrome b protein. Furthermore, in patient cells, cytochrome b is absent from a high-molecular-weight complex III. UQCC3 is reduced in cells depleted for the complex III assembly factors UQCC1 and UQCC2. Conversely, absence of UQCC3 in patient cells does not affect UQCC1 and UQCC2. This suggests that UQCC3 functions in the complex III assembly pathway downstream of UQCC1 and UQCC2 and is consistent with what is known about the function of Cbp4 and of the fungal orthologs of UQCC1 and UQCC2, Cbp3 and Cbp6. We conclude that UQCC3 functions in complex III assembly and that the c.59T>A mutation has a causal role in complex III deficiency.

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

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.