Mitochondrial protein import: precursor oxidation in a ternary complex with disulfide carrier and sulfhydryl oxidase

The biogenesis of mitochondrial intermembrane space proteins depends on specific machinery that transfers disulfide bonds to precursor proteins. The machinery shares features with protein relays for disulfide bond formation in the bacterial periplasm and endoplasmic reticulum. A disulfide-generating enzyme/sulfhydryl oxidase oxidizes a disulfide carrier protein, which in turn transfers a disulfide to the substrate protein. Current views suggest that the disulfide carrier alternates between binding to the oxidase and the substrate. We have analyzed the cooperation of the disulfide relay components during import of precursors into mitochondria and identified a ternary complex of all three components. The ternary complex represents a transient and intermediate step in the oxidation of intermembrane space precursors, where the oxidase Erv1 promotes disulfide transfer to the precursor while both oxidase and precursor are associated with the disulfide carrier Mia40

Preserved respiratory chain capacity and physiology in mice with profoundly reduced levels of mitochondrial respirasomes

The mammalian respiratory chain complexes I, III 2, and IV (CI, CIII 2, and CIV) are critical for cellular bioenergetics and form a stable assembly, the respirasome (CI-CIII 2-CIV), that is biochemically and structurally well documented. The role of the respirasome in bioenergetics and the regulation of metabolism is subject to intense debate and is difficult to study because the individual respiratory chain complexes coexist together with high levels of respirasomes. To critically investigate the in vivo role of the respirasome, we generated homozygous knockin mice that have normal levels of respiratory chain complexes but profoundly decreased levels of respirasomes. Surprisingly, the mutant mice are healthy, with preserved respiratory chain capacity and normal exercise performance. Our findings show that high levels of respirasomes are dispensable for maintaining bioenergetics and physiology in mice but raise questions about their alternate functions, such as those relating to the regulation of protein stability and prevention of age-associated protein aggregation

Bronchiectasis and asthma:Data from the European Bronchiectasis Registry (EMBARC)

Background: Asthma is commonly reported in patients with a diagnosis of bronchiectasis. Objective: The aim of this study was to evaluate whether patients with bronchiectasis and asthma (BE+A) had a different clinical phenotype and different outcomes compared with patients with bronchiectasis without concomitant asthma. Methods: A prospective observational pan-European registry (European Multicentre Bronchiectasis Audit and Research Collaboration) enrolled patients across 28 countries. Adult patients with computed tomography–confirmed bronchiectasis were reviewed at baseline and annual follow-up visits using an electronic case report form. Asthma was diagnosed by the local investigator. Follow-up data were used to explore differences in exacerbation frequency between groups using a negative binomial regression model. Survival analysis used Cox proportional hazards regression. Results: Of 16,963 patients with bronchiectasis included for analysis, 5,267 (31.0%) had investigator-reported asthma. Patients with BE+A were younger, were more likely to be female and never smokers, and had a higher body mass index than patients with bronchiectasis without asthma. BE+A was associated with a higher prevalence of rhinosinusitis and nasal polyps as well as eosinophilia and Aspergillus sensitization. BE+A had similar microbiology but significantly lower severity of disease using the bronchiectasis severity index. Patients with BE+A were at increased risk of exacerbation after adjustment for disease severity and multiple confounders. Inhaled corticosteroid (ICS) use was associated with reduced mortality in patients with BE+A (adjusted hazard ratio 0.78, 95% CI 0.63-0.95) and reduced risk of hospitalization (rate ratio 0.67, 95% CI 0.67-0.86) compared with control subjects without asthma and not receiving ICSs. Conclusions: BE+A was common and was associated with an increased risk of exacerbations and improved outcomes with ICS use. Unexpectedly we identified significantly lower mortality in patients with BE+A.</p

Objective sputum colour assessment and clinical outcomes in bronchiectasis: data from the European Bronchiectasis Registry (EMBARC)

Background A validated 4-point sputum colour chart can be used to objectively evaluate the levels of airway inflammation in bronchiectasis patients. In the European Bronchiectasis Registry (EMBARC), we tested whether sputum colour would be associated with disease severity and clinical outcomes. Methods We used a prospective, observational registry of adults with bronchiectasis conducted in 31 countries. Patients who did not produce spontaneous sputum were excluded from the analysis. The Murray sputum colour chart was used at baseline and at follow-up visits. Key outcomes were frequency of exacerbations, hospitalisations for severe exacerbations and mortality during up to 5-year follow-up. Results 13 484 patients were included in the analysis. More purulent sputum was associated with lower forced expiratory volume in 1 s (FEV 1), worse quality of life, greater bacterial infection and a higher bronchiectasis severity index. Sputum colour was strongly associated with the risk of future exacerbations during follow-up. Compared to patients with mucoid sputum (reference group), patients with mucopurulent sputum experienced significantly more exacerbations (incident rate ratio (IRR) 1.29, 95% CI 1.22–1.38; p&lt;0.0001), while the rates were even higher for patients with purulent (IRR 1.55, 95% CI 1.44–1.67; p&lt;0.0001) and severely purulent sputum (IRR 1.91, 95% CI 1.52–2.39; p&lt;0.0001). Hospitalisations for severe exacerbations were also associated with increasing sputum colour with rate ratios, compared to patients with mucoid sputum, of 1.41 (95% CI 1.29–1.56; p&lt;0.0001), 1.98 (95% CI 1.77–2.21; p&lt;0.0001) and 3.05 (95% CI 2.25–4.14; p&lt;0.0001) for mucopurulent, purulent and severely purulent sputum, respectively. Mortality was significantly increased with increasing sputum purulence, hazard ratio 1.12 (95% CI 1.01–1.24; p=0.027), for each increment in sputum purulence. Conclusion Sputum colour is a simple marker of disease severity and future risk of exacerbations, severe exacerbations and mortality in patients with bronchiectasis.</p

Bronchiectasis and asthma:Data from the European Bronchiectasis Registry (EMBARC)

Background: Asthma is commonly reported in patients with a diagnosis of bronchiectasis. Objective: The aim of this study was to evaluate whether patients with bronchiectasis and asthma (BE+A) had a different clinical phenotype and different outcomes compared with patients with bronchiectasis without concomitant asthma. Methods: A prospective observational pan-European registry (European Multicentre Bronchiectasis Audit and Research Collaboration) enrolled patients across 28 countries. Adult patients with computed tomography–confirmed bronchiectasis were reviewed at baseline and annual follow-up visits using an electronic case report form. Asthma was diagnosed by the local investigator. Follow-up data were used to explore differences in exacerbation frequency between groups using a negative binomial regression model. Survival analysis used Cox proportional hazards regression. Results: Of 16,963 patients with bronchiectasis included for analysis, 5,267 (31.0%) had investigator-reported asthma. Patients with BE+A were younger, were more likely to be female and never smokers, and had a higher body mass index than patients with bronchiectasis without asthma. BE+A was associated with a higher prevalence of rhinosinusitis and nasal polyps as well as eosinophilia and Aspergillus sensitization. BE+A had similar microbiology but significantly lower severity of disease using the bronchiectasis severity index. Patients with BE+A were at increased risk of exacerbation after adjustment for disease severity and multiple confounders. Inhaled corticosteroid (ICS) use was associated with reduced mortality in patients with BE+A (adjusted hazard ratio 0.78, 95% CI 0.63-0.95) and reduced risk of hospitalization (rate ratio 0.67, 95% CI 0.67-0.86) compared with control subjects without asthma and not receiving ICSs. Conclusions: BE+A was common and was associated with an increased risk of exacerbations and improved outcomes with ICS use. Unexpectedly we identified significantly lower mortality in patients with BE+A.</p

Objective sputum colour assessment and clinical outcomes in bronchiectasis: data from the European Bronchiectasis Registry (EMBARC)

Background A validated 4-point sputum colour chart can be used to objectively evaluate the levels of airway inflammation in bronchiectasis patients. In the European Bronchiectasis Registry (EMBARC), we tested whether sputum colour would be associated with disease severity and clinical outcomes. Methods We used a prospective, observational registry of adults with bronchiectasis conducted in 31 countries. Patients who did not produce spontaneous sputum were excluded from the analysis. The Murray sputum colour chart was used at baseline and at follow-up visits. Key outcomes were frequency of exacerbations, hospitalisations for severe exacerbations and mortality during up to 5-year follow-up. Results 13 484 patients were included in the analysis. More purulent sputum was associated with lower forced expiratory volume in 1 s (FEV 1), worse quality of life, greater bacterial infection and a higher bronchiectasis severity index. Sputum colour was strongly associated with the risk of future exacerbations during follow-up. Compared to patients with mucoid sputum (reference group), patients with mucopurulent sputum experienced significantly more exacerbations (incident rate ratio (IRR) 1.29, 95% CI 1.22–1.38; p&lt;0.0001), while the rates were even higher for patients with purulent (IRR 1.55, 95% CI 1.44–1.67; p&lt;0.0001) and severely purulent sputum (IRR 1.91, 95% CI 1.52–2.39; p&lt;0.0001). Hospitalisations for severe exacerbations were also associated with increasing sputum colour with rate ratios, compared to patients with mucoid sputum, of 1.41 (95% CI 1.29–1.56; p&lt;0.0001), 1.98 (95% CI 1.77–2.21; p&lt;0.0001) and 3.05 (95% CI 2.25–4.14; p&lt;0.0001) for mucopurulent, purulent and severely purulent sputum, respectively. Mortality was significantly increased with increasing sputum purulence, hazard ratio 1.12 (95% CI 1.01–1.24; p=0.027), for each increment in sputum purulence. Conclusion Sputum colour is a simple marker of disease severity and future risk of exacerbations, severe exacerbations and mortality in patients with bronchiectasis.</p

Biogenesis of the mitochondrial TOM complex: Mim1 promotes insertion and assembly of signal-anchored receptors.

The translocase of the outer membrane (TOM complex) is the central entry gate for nuclear-encoded mitochondrial precursor proteins. All Tom proteins are also encoded by nuclear genes and synthesized as precursors in the cytosol. The channel-forming ␤-barrel protein Tom40 is targeted to mitochondria via Tom receptors and inserted into the outer membrane by the sorting and assembly machinery (SAM complex). A further outer membrane protein, Mim1, plays a less defined role in assembly of Tom40 into the TOM complex. The three receptors Tom20, Tom22, and Tom70 are anchored in the outer membrane by a single transmembrane ␣-helix, located at the N terminus in the case of Tom20 and Tom70 (signal-anchored) or in the C-terminal portion in the case of Tom22 (tail-anchored). Insertion of the precursor of Tom22 into the outer membrane requires pre-existing Tom receptors while the import pathway of the precursors of Tom20 and Tom70 is only poorly understood. We report that Mim1 is required for efficient membrane insertion and assembly of Tom20 and Tom70, but not Tom22. We show that Mim1 associates with SAM core components to a large SAM complex, explaining its role in late steps of the assembly pathway of Tom40. We conclude that Mim1 is not only required for biogenesis of the ␤-barrel protein Tom40 but also for membrane insertion and assembly of signal-anchored Tom receptors. Thus, Mim1 plays an important role in the efficient assembly of the mitochondrial TOM complex. The essential biochemical function of mitochondria depends on the uptake of cytosolic-synthesized precursor proteins. The vast majority of precursor proteins are imported by the preprotein translocase of the outer mitochondrial membrane (TOM 4 complex). Subsequently the precursor proteins are sorted to the different mitochondrial subcompartments, the outer and inner membranes, the intermembrane space and the matrix (1-7). The TOM complex is composed of seven different subunits. Tom40 forms the protein-conducting channel across the outer membrane (8 -10). The three receptors Tom20, Tom22, and Tom70 expose domains on the cytosolic side of the outer membrane, recognize the precursor proteins and direct them to the Tom40 channel (11). In addition, three small Tom proteins, Tom5, Tom6, and Tom7, are associated with the Tom40 core of the complex (12-14). Tom40 forms a transmembrane ␤-barrel, while all other Tom components are embedded in the membrane via a single transmembrane ␣-helix (9 -10, 15). The ␣-helical membrane anchor is localized in the C-terminal portion of Tom22 and the small Tom proteins and thus those proteins belong to the tail-anchored proteins (15-19). Tom20 and Tom70 are integrated into the outer membrane by an N-terminal ␣-helix, which together with flanking regions is important for both intracellular targeting and membrane anchoring, and thus these proteins are called signal-anchored proteins (20 -23). All Tom proteins are synthesized as precursor proteins on cytosolic ribosomes and imported into mitochondria. The import pathway of the precursor of the channel-forming protein Tom40 has been studied in detail. The ␤-barrel precursor is recognized by TOM receptors and translocated across the outer membrane by a pre-existing Tom40 channel (24 -26). On the intermembrane space side, chaperone complexes formed by small Tim proteins transfer the precursor of Tom40 to the sorting and assembly machinery (SAM complex) that promotes insertion of the precursor into the outer membran