Photosystem I light-harvesting proteins regulate photosynthetic electron transfer and hydrogen production

Linear electron flow (LEF) and cyclic electron flow (CEF) compete for light-driven electrons transferred from the acceptor side of photosystem I (PSI). Under anoxic conditions, such highly reducing electrons also could be used for hydrogen (H2) production via electron transfer between ferredoxin and hydrogenase in the green alga Chlamydomonas reinhardtii. Partitioning between LEF and CEF is regulated through PROTON-GRADIENT REGULATION5 (PGR5). There is evidence that partitioning of electrons also could be mediated via PSI remodeling processes. This plasticity is linked to the dynamics of PSI-associated light-harvesting proteins (LHCAs) LHCA2 and LHCA9. These two unique light-harvesting proteins are distinct from all other LHCAs because they are loosely bound at the PSAL pole. Here, we investigated photosynthetic electron transfer and H2 production in single, double, and triple mutants deficient in PGR5, LHCA2, and LHCA9. Our data indicate that lhca2 and lhca9 mutants are efficient in photosynthetic electron transfer, that LHCA2 impacts the pgr5 phenotype, and that pgr5/lhca2 is a potent H2 photo-producer. In addition, pgr5/lhca2 and pgr5/lhca9 mutants displayed substantially different H2 photo-production kinetics. This indicates that the absence of LHCA2 or LHCA9 impacts H2 photo-production independently, despite both being attached at the PSAL pole, pointing to distinct regulatory capacities

Current Developments and Challenges in the Recycling of Key Components of (Hybrid) Electric Vehicles

The introduction of electromobility causes major challenges as new components and materials enter vehicle recycling. This paper discusses the current developments in the recycling of traction batteries, electric motors, and power electronics, which constitute the key components of (hybrid) electric vehicles. Both technical and ecological aspects are addressed. Beside base metals, all components contain metals that are considered critical by the EU (European Union), e.g., rare earth elements, cobalt, antimony, and palladium. As electromobility is a new trend, no recycling routes have been established at an industrial scale for these components. The implementation is complicated by small return flows and a great variety of vehicle concepts as well as components. Furthermore, drastic changes regarding design and material compositions can be expected over the next decades. Due to hazards and high weights, there is a strong research emphasis on battery recycling. Most pilot-scale or semi-industrial processes focus on the recovery of cobalt, nickel, and copper due to their high value. Electric motors and power electronics can be fed into established recycling routes if they are extracted from the vehicle before shredding. However, these processes are not capable of recovering some minor metals such as rare earth elements and antimony

The chloroplast ATP synthase upon oxidative stress : critical targets of reactive oxygen species

This study examines the impact of reactive oxygen species on enzymatic activity of the chloroplast ATP synthase in situ and in vitro. Isolated spinach thylakoids were shown to be less catalytically active upon treatment with singlet oxygen. It was demonstrated that exposed thylakoids lost their capacity to synthesize and hydrolyze ATP and to acidify the thylakoid lumen in an ATP-dependent manner. A central element of the study was the identification of specific target sites which could be solved in the course of the project. Structural predictions upon enzymatic redox-regulation served as a first platform for this approach. Purification of soluble catalytic CF1 protein revealed that ATPase activity in vitro attenuated by singlet oxygen in a comparable manner to the reaction in situ. With the help of a stepwise disassembly approach it could be shown that initially suggested inter-subunit cross-links between regulatory subunits were not responsible for singlet oxygen-induced loss of activity. Instead, the CF1 gamma subunit seemed to be a promising candidate that harbored functional targets responsible for activity attenuation. In silico analysis proposed a gamma subunit methionine-cysteine cluster to form a highly conserved set of potential targets of various reactive oxygen species. Further mass spectrometry analysis revealed that these residues were susceptible to singlet oxygen and hydrogen peroxide. Several point mutations within in the cluster were analyzed using a recombinant photosynthetic F-ATP synthase assembly system. In an extensive biochemical mutant characterization screen it could be demonstrated that some mutants displayed an aberration of catalytic properties, such as MgADP binding propensity and activity regulation by the gamma subunit redox state. The cluster residues were ascribed to mutually interact while having an effect on remote functional domains within the enzyme. Finally, it could be shown that oxidation of the cluster was responsible for hydrogen peroxide-induced activity attenuation. It is very likely that additional residues participate in singlet oxygen-dependent loss of activity.Gegenstand der Arbeit ist die Untersuchung des Einflusses von reaktiven Sauerstoffspezies auf die Enzymaktivität der plastidären ATP-Synthase in situ und in vitro. An isolierten Thylakoiden aus Spinat wurde eine verminderte katalytische Aktivität nach Kontakt mit Singulett-Sauerstoff gemessen. So konnte gezeigt werden, dass von behandelten Thylakoiden sowohl weniger ATP synthetisiert als auch hydrolysiert wurde. Zudem wiesen die Proben einen eingeschränkten Protonentransport in das Thylakoidlumen nach ATP-Zugabe auf. Die Identifizierung spezifischer Angriffsstellen für reaktive Sauerstoffspezies war zentraler Gegenstand der Studie. Demnach wurde der beobachtete Aktivitätsabfall in Abhängigkeit vom Redoxzustand des Enzyms auf Strukturänderungen zurückgeführt. Die Aufreinigung und Analyse der löslichen CF1-Komponente deutete darauf hin, dass die Aktivitätsabnahme durch Singulett-Sauerstoff in vitro der Abnahme des Enzyms in situ ähnelte. Cross-Links zwischen regulatorischen Untereinheiten von CF1, die ursprünglich für den Abfall durch Singulett-Sauerstoff verantwortlich gemacht wurden, konnten durch graduelle Demontage ausgeschlossen werden. Besonderheiten, die mittels Strukturmodellanalyse aufgezeigt werden konnten, deuteten darauf hin, dass die gamma Untereinheit von CF1 funktionelle Angriffsziele für Singulett-Sauerstoff enthält. Begleitend dazu ergaben massenspektrometrische Untersuchungen, dass ein konserviertes Cluster in der gamma Untereinheit, bestehend aus Methioninen und Cystein, durch Singulett-Sauerstoff und Wasserstoffperoxid oxidiert wurde. Eine Analyse entsprechender Punkt-Mutationen an den Zielaminosäuren erfolgte in einem Assemblierungssystem von rekombinanten Untereinheiten aus photosynthetischen ATP-Synthasen. So konnte gezeigt werden, dass die untersuchten Mutanten katalytische Veränderungen aufwiesen, wie beispielsweise Bindungsstärke von MgADP oder Redox-Regulierung der Enzymaktivität. Es wurden dabei Hinweise für Interaktionen innerhalb des Clusters gefunden. Zudem hatte die interagierende Gruppe an Aminosäuren weitreichende Einflüsse auf funktionelle Strukturen im Enzym. Letztendlich wurde die wesentliche Zielsetzung der Studie erfüllt, indem mittels der Mutanten gezeigt werden konnte, dass eine Oxidation der postulierten Angriffsziele in der gamma Untereinheit durch Wasserstoffperoxid zur Aktivitätsabnahme beitrug. Gleiches galt für Singulett-Sauerstoff, jedoch deuten die Daten auf ein Zusammenspiel mit weiteren Resten hin

White matter is increased in the brains of adults with neurofibromatosis 1

Background Neurofibromatosis 1 (NF1) is a rare autosomal dominant disease characterized by increased Schwann cell proliferation in peripheral nerves. Several small studies of brain morphology in children with NF1 have found increased total brain volume, total white matter volume and/or corpus callosum area. Some studies (mostly in children with NF1) also attempted to correlate changes in brain morphology and volume with cognitive or behavioural abnormalities, although the findings were inconsistent. We aimed to characterize alterations in brain volumes by three-dimensional (3D) MRI in adults with NF1 in major intracranial sub-regions. We also aimed to assess the effect of age on these volumes and correlated brain white matter and grey matter volumes with neuropsychometric findings in adults with NF1. Methods We obtained brain volume measurements using 3D magnetic resonance imaging for 351 adults with NF1 and, as a comparison group, 43 adults with neurofibromatosis 2 (NF2) or Schwannomatosis. We assessed a subset of 19 adults with NF1 for clinical severity of NF1 features and neurological problems and conducted psychometric testing for attention deficiencies and intelligence quotient. We compared brain volumes between NF1 patients and controls and correlated volumetric measurements to clinical and psychometric features in the NF1 patients. Results Total brain volume and total and regional white matter volumes were all significantly increased in adults with NF1. Grey matter volume decreased faster with age in adults with NF1 than in controls. Greater total brain volume and white matter volume were correlated with lower attention deficits and higher intelligence quotients in adults with NF1. Conclusion Our findings are consistent with the hypothesis that dysregulation of brain myelin production is a cardinal manifestation of NF1 and that these white matter changes may be functionally important in affected adults.Medicine, Faculty ofNon UBCMedical Genetics, Department ofReviewedFacult

Alterations in brain morphology by MRI in adults with neurofibromatosis 1

Objective Neurofibromatosis 1 (NF1) is a rare autosomal dominant disease that causes the dysregulated growth of Schwann cells. Most reported studies of brain morphology in NF1 patients have included only children, and clinical implications of the observed changes later in life remain unclear. In this study, we used MRI to characterize brain morphology in adults with NF1. Methods Planar (2D) MRI measurements of 29 intracranial structures were compared in 389 adults with NF1 and 112 age- and sex-matched unaffected control subjects. The 2D measurements were correlated with volumetric (3D) brain measurements in 99 of the adults with NF1 to help interpret the 2D findings. A subset (n = 70) of these NF1 patients also received psychometric testing for attention deficits and IQ and was assessed for clinical severity of NF1 features and neurological problems. Correlation analysis was performed between the MRI measurements and clinical and psychometric features of these patients. Results Four of nine corpus callosum measurements were significantly greater in adults with NF1 than in sex- and age-matched controls. All seven brainstem measurements were significantly greater in adults with NF1 than in controls. Increased corpus callosum and brainstem 2D morphology were correlated with increased total white matter volume among the NF1 patients. No robust correlations were observed between the 2D size of these structures and clinical or neuropsychometric assessments. Conclusion Our findings are consistent with the hypothesis that dysregulation of brain myelin production is an important manifestation of NF1 in adults.Medicine, Faculty ofNon UBCMedical Genetics, Department ofReviewedFacultyResearcherOthe

Chloroplasts require glutathione reductase to balance reactive oxygen species and maintain efficient photosynthesis

Thiol-based redox-regulation is vital for coordinating chloroplast functions depending on illumination and has been throroughly investigated for thioredoxin-dependent processes. In parallel, glutathione reductase (GR) maintains a highly reduced glutathione pool, enabling glutathione-mediated redox buffering. Yet, how the redox cascades of the thioredoxin and glutathione redox machineries integrate metabolic regulation and detoxification of reactive oxygen species remains largely unresolved because null mutants of plastid/mitochondrial GR are embryo-lethal in Arabidopsis thaliana. To investigate whether maintaining a highly reducing stromal glutathione redox potential (E-GSH) via GR is necessary for functional photosynthesis and plant growth, we created knockout lines of the homologous enzyme in the model moss Physcomitrella patens. In these viable mutant lines, we found decreasing photosynthetic performance and plant growth with increasing light intensities, whereas ascorbate and zeaxanthin/antheraxanthin levels were elevated. By in vivo monitoring stromal E-GSH dynamics, we show that stromal E-GSH is highly reducing in wild-type and clearly responsive to light, whereas an absence of GR leads to a partial glutathione oxidation, which is not rescued by light. By metabolic labelling, we reveal changing protein abundances in the GR knockout plants, pinpointing the adjustment of chloroplast proteostasis and the induction of plastid protein repair and degradation machineries. Our results indicate that the plastid thioredoxin system is not a functional backup for the plastid glutathione redox systems, whereas GR plays a critical role in maintaining efficient photosynthesis