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The Real and Financial Impact of COVID-19 Around the World
No full textIn this paper, we study the impact of the COVID-19 pandemic in estimated panel VAR models for 92 countries. The large cross section of countries allows us to shed light on the heterogeneity of the responses of stock markets and NO2 emissions as high-frequency measures of economic activity. We quantify the effect of the number of infections and four dimensions of policy measures: (1) containment and closure, (2) movement restrictions, (3) economic support and (4) adjustments of health systems. Our main findings show that a surprise increase in the number of infections triggers a drop in our two measures of economic activity. Propping up economic support measures, in contrast, raises stock returns and emissions and, thus, contributes to the economic recovery. We also document vast differences in the responses across subsets of countries and between the first and the second wave of infections
Sex, landscape diversity and primary productivity shape the seasonal space use of a migratory European raptor
No full textIntrinsic and extrinsic drivers shape the space use of wide-ranging raptors. A large proportion of raptors are migrants that shift their activity ranges between summer and winter habitats, where they encounter different environmental conditions. Analysing the effects of intrinsic and extrinsic drivers on the space use in summer and win-ter habitats provides crucial insights into the ecology of migratory raptors. Here, we investigated the seasonal space use by 43 red kites Milvus milvus tracked by GPS-transmitters across central and south-western Europe over seven consecutive years. We compared space use patterns, i.e. activity range sizes and mean daily distances of the birds between summer and winter, and analysed the influence of extrinsic (landscape diversity, primary productivity) and intrinsic factors (sex). Within summer, we inves-tigated the influence of breeding success and sex on activity range sizes. We further analysed differences in habitat availability and habitat selection between seasons. We found that space use was smaller in summers than in winters. When compared to those of males, activity ranges of female red kites were larger in summers and smaller in winters, with shorter mean daily distances in both seasons. Within summer, suc-cessfully breeding red kites had smaller activity range sizes in both sexes, but this effect was stronger in females than in males. Regardless of the season, landscape diversity was positively correlated with space use, whereas primary productivity was negatively cor-related with it. The habitat use differed between seasons, with agricultural landscapes being less proportionally used in summers than in winters. Overall, we showed that both intrinsic and extrinsic drivers shaped space use in both seasons, leading to differ-ences in space use patterns and habitat use in migratory raptors between their summer and winter habitats. Our findings underline the importance of consideration of the entire annual cycle of migratory species for conservation management.Gefördert durch den Open-Access-Publikationsfonds der UB Marburg
Drought and property Prices: Empirical Evidence from Iran
No full textThis study demonstrates an economic consequence of climate change and water crises in Iran. It examines the effect of drought on housing prices, residential land prices, and housing rents in Iran. Using data from provinces of Iran from 1993 to 2015 and applying static and dynamic panel fixed effects estimators, we find evidence that an increase in the balance of water (reducing the severity of drought) within provinces has a positive effect on property prices. Our results have important implications for Iranian policymakers and property investors
Investigations on the selectivity of interactions between selected G protein-coupled receptors with downstream effectors and their pharmacological influence
No full textMit über 800 Vertretern im menschlichen Genom stellen GPCRs die größte Gruppe der Membranrezeptoren dar. Sie sind involviert in eine Vielzahl physiologischer Vorgänge und stellen mit über 30 Prozent der zugelassenen Arzneimittel, die an GPCRs angreifen, ein wichtiges Arzneistofftarget dar. Die Entwicklung selektiver Arzneimittel ist bei Adressierung der orthosterischen, meist evolutionär hochkonservierten Bindetasche innerhalb einer Rezeptorfamilie, eine große Herausforderung. Dementsprechend ist das Interesse der Forschung und Pharmaindustrie an der Untersuchung und Entwicklung von einerseits allosterischen Modulatoren, die an alternative, weniger konservierte Epitope binden und die Rezeptoraktivität modulieren können und andererseits von biased-Agonisten, die zu einer selektiven und präferierten Aktivierung eines Signalweges führen, stark angestiegen. Beide Arten von Liganden sollen zu einer Erhöhung der Selektivität von Arzneistoffen, einhergehend mit weniger unerwünschten Arzneimittelwirkungen führen.
In den ersten Teilen dieser Arbeit lag das Augenmerk auf der allosterischen Modulation von Rezeptoren. Dabei war das Ziel in Zusammenarbeit mit verschiedenen Arbeitsgruppen neue allosterische Liganden am EndothelinB-Rezeptor (ETB) zu identifizieren und deren Wirkung auf den Rezeptor zu untersuchen. Dazu wurden die mithilfe von Docking (AG Kolb) identifizierten niedermolekularen Compounds, die überwiegend in die intrazelluläre G-Protein-Bindetasche des ETB-Rezeptors gedockt wurden, in verschiedenen FRET-basierten Assays auf eine mögliche Modulation der Rezeptoraktivität hin untersucht. Bisher konnte jedoch kein Compound mit einem ausreichenden Effekt auf die Rezeptorfunktion identifiziert werden, was die Komplexität der allosterischen Wirkstoffentwicklung widerspiegelt. Für ein Compound, AW12, welches zur allosterischen Modulation des M2-Rezeptors durch Bindung an die intrazelluläre Kavität entwickelt wurde, konnte hingegen eine Abschwächung der G-Protein-Bindung an den M2-Rezeptor nachgewiesen werden.
In einem weiteren Teil dieser Arbeit wurde die funktionale Relevanz neu identifizierter, zuvor nicht adressierter, allosterischer Bindetaschen am M3-Rezeptor nachgewiesen. Dazu wurden Punktmutationen im Bereich der beiden Bindetaschen in den Rezeptor eingeführt. Es konnte sowohl eine Änderung der Affinität von Acetylcholin als auch eine Verminderung der Effektivität des Partialagonisten Arecolin in der G-Protein-Aktivierung nachgewiesen werden. Zusätzlich führten die Mutationen zu einer Verringerung der Effektivität von Acetylcholin in der Arrestin-Rekrutierung. Alle Mutationen in den Regionen der beiden Bindetaschen am M3-Rezeptor führten zu deutlichen Änderungen in der Funktion des Rezeptors, was suggeriert, dass die Rezeptorfunktion durch Bindung von allosterischen Modulatoren in diese zu dem Zeitpunkt noch nicht adressierten Bindetaschen beeinflusst werden kann.
In einem weiteren Kapitel wurde der Orphan-Rezeptor GPRC5B näher untersucht. Mithilfe von FRAP-basierten Messungen konnte eine Interaktion der Rezeptoren, die eine Dimerisierung suggeriert, nachgewiesen werden. Hingegen konnte eine mögliche G-Protein-Kopplung des Rezeptors unter Nukleotid-freien Bedingungen nicht identifiziert werden.
Die über 800 GPCRs im menschlichen Genom koppeln an nur 16 verschiedene Gα-Proteine, die in 4 Familien eingeteilt sind. Trotz jahrelanger Forschung konnte bisher kein Mechanismus der Kopplungsselektivität identifiziert werden. Die vermehrten Kristall- und Kryo-EM-Strukturen der Rezeptor-G-Protein-Komplexe in den letzten Jahren konnten zwar einen Einblick in die Interaktion von G-Protein und GPCR bringen, jedoch sind sie nur Momentaufnahmen eines komplexen Vorgangs. Auch zur Adressierung der G-Protein-Bindetasche durch allosterische Modulatoren ist ein Verständnis der Rezeptorstrukturen, die in die Interaktionen mit dem G-Protein und die Kopplungsselektivität maßgeblich beteiligt sind, von großem Vorteil. Im Rahmen dieser Arbeit wurden M2- und M3-basierte Rezeptorchimären erstellt und in FRET- und BRET-basierten Assays vermessen, um wichtige Rezeptorstrukturen der selektiven Bindung von Gαo und/oder Gαq zu identifizieren. Dabei konnten die unteren Abschnitte der Transmembrandomänen 5 und 6, wie auch der polybasische Abschnitt am proximalen C-Terminus und der distale C-Terminus des M3-Rezeptors als wichtige Strukturen für die Kopplung der G-Proteine identifiziert werden.
Im letzten Teil dieser Arbeit lag das Augenmerk auf einem Agonisten-Bias am M3-Rezeptor. Hierbei wurde die direkte Rekrutierung der Effektorproteine zum Rezeptor in FRET-basierten Assays unter Bedingungen, die eine klare Trennung der Signalwege voneinander erlaubten, untersucht. Dabei konnte ein Bias auf Ebene der Arrestin-Rekrutierung nachgewiesen werden, der jedoch nicht auf Ebene der GRK2-Rekrutierung nachzuweisen war. Dies brachte neue Erkenntnisse in die bisher wenig im Rahmen von Bias erforschte GRK2-Rekrutierung.
Insgesamt ermöglicht die Arbeit neue Einblicke in die komplexen Vorgänge der allosterischen Modulation von GPCRS, der selektiven Bindung von G-Proteinen und der Agonist-induzierten funktionalen Selektivität von Rezeptoren.With more than 800 individuals GPCRs are known to be largest group of membrane spanning receptors in the human genome. They are involved in various physiological processes and are therefore a significant drug target, represented by more than 30 percent of approved drugs binding to GPCRs. The development of selective drugs is a considerable challenge when targeting the orthosteric binding pocket, being evolutionary highly conserved within a given receptor family. Hence, there has been an increasing interest on the part of research and the pharmaceutical industry in the examination and development of allosteric modulators on the one hand, which target alternative less conserved binding pockets and modulate receptor activity, and biased agonists on the other hand, which lead to a selective and preferred activation of a signalling pathway. Both kinds of ligands are supposed to increase the selectivity of drugs and reduce side effects.
The first parts of this thesis focused on the allosteric modulation of GPCRs. The goal was to identify allosteric ligands targeting the endothelinB receptor (ETB) and examine their impact on receptors function, cooperating with different working groups. For that purpose, the through docking identified small compounds were analysed regarding a potential modulation of receptor function using FRET-based assays. The tested compounds were docked to the G protein binding pocket of the ETB receptor. Up until now no compound with a sufficient modulation of receptor activity has been discovered, depicting the complexity of allosteric drug development. For the AW12 compound, which was modelled to allosterically modulate the M2 receptor by binding to the intracellular cavity, a decrease in G protein binding to the M2 receptor was detected.
In another part of this thesis the functional relevance of newly identified, previously untargeted binding pockets at the M3 receptor was proven. Point mutations were inserted into the receptor in the regions of the two binding pockets. A change in the affinity of acteylcholin as well as a decrease in efficacy of arecoline in the G protein activation was measured. In addition, the mutations led to a reduction in efficacy of acetylcholine in arrestin recruitment. All mutations in the regions of both binding pockets at the M3 receptor resulted in considerable changes in receptor function, suggesting that receptor function can be influenced by the binding of allosteric ligands into these previously untargeted sites.
In another chapter the orphan receptor GPRC5B was investigated further. In FRAP-based measurements an interaction of the receptors was observed, suggesting a dimerization. However, a potential G protein binding under nucleotide free conditions could not be detected.
The more than 800 GPCRs in humans couple to merely 16 different Gα proteins, divided into 4 families. Despite of long-lasting research no mechanism of coupling selectivity has been identified up until now. The increased crystal and cryo-EM structures of receptor-G protein complexes of recent years provided an insight into the interaction of G protein and receptor. However, they are only snapshots of a complex mechanism. Understanding receptor structures, which are considerably involved in the interaction with the G protein and the coupling selectivity, is of notable advantage when addressing the G protein binding pocket with allosteric modulators. For this thesis M2- and M3-based receptor chimeras were generated and investigated in FRET- and BRET-based assays, in order to identify crucial receptor structures involved in the selective binding of Gαo and Gαq. As a result, the lower parts of transmembrane helices 5 and 6, the polybasic cluster at the proximal c terminus and the distal c terminus of the M3 receptor were detected as important structures for coupling selectivity.
The final part of this thesis focused on the agonist bias at the M3 receptor. In this regard, the direct recruitment of effector proteins to the receptor in FRET-based assays was examined, under conditions which allowed a clear separation between the signalling pathways. This led to a detection of a bias in arrestin recruitment, which, however, could not be found on the level of GRK2 recruitment. As a result, new insights were gained into the previously poorly researched GRK2 recruitment in the context of bias.
Overall, this thesis contributes further insights into the complex mechanisms of allosteric modulation, the selective binding of G proteins and the agonist induced functional selectivity of GPCRs
The Relationship between Pro-environmental Behavior, Economic Preferences, and Life Satisfaction: Empirical Evidence from Germany
No full textBased on representative data for 1614 citizens in Germany, this paper empirically examines the relationship between different types of environmental protection activities and subjective well-being (SWB) in terms of life satisfaction by specifically considering the role of economic pref-erences for this relationship. With respect to pro-environmental behavior, we differentiate be-tween stated non-climate environmental and climate protection activities as well as revealed climate protection activities, which are measured in an incentivized donation experiment and thus are more meaningful than stated climate protection activities. Our empirical analysis re-veals that climate protection activities are more robustly and more strongly positively correlated with life satisfaction than non-climate environmental protection activities. Furthermore, not only stated climate protection activities, but also revealed climate protection activities are sig-nificantly positively correlated with life satisfaction. These results suggest that climate protec-tion activities lead to stronger warm glow feelings and reputation gains than non-climate envi-ronmental protection activities. Our empirical analysis additionally shows that economic pref-erences play an important role since especially patience and trust, but also risk-taking prefer-ences and (less robust) altruism are significantly positively correlated with life satisfaction. In particular, economic preferences are also relevant for the relationship between pro-environmen-tal behavior and life satisfaction. When economic preferences are included in the econometric analysis, the estimated correlations between climate protection activities and life satisfaction become weaker and the estimated correlation between non-climate environmental protection activities and life satisfaction even becomes insignificant. These results strongly suggest omit-ted variable biases in cross-sectional econometric analyses of the relationship between pro-environmental behavior and SWB when economic preferences are not included as control variables
Sectoral FDI and Economic Growth — Evidence from Egyptian Governorates
No full textThis paper investigates the effect of sectoral foreign direct investment (FDI) on economic growth in Egypt, using a novel panel dataset of 26 Egyptian governorates for the period 1992–2007. The growth literature is robust with the benefits of using a within-country dataset for such a research question (Ford et al., 2008). Despite the large number of theoretical models on the channels through which FDI can enhance economic growth, empirical findings are still inconclusive. We argue that one possible reason for the ambiguous effect is the use of aggregate FDI data across different sectors. Our results show no significant effect of aggregate FDI stock on economic growth in Egyptian governorates, which can be partly explained by the contradictory growth effects of FDI at the sectoral level. We find a positive effect of manufacturing FDI, a negative effect of agricultural FDI and no significant effect of services FDI on economic growth
Umgang mit politischer Gewalt in konfliktreichen Demokratien: Transitional Justice im Libanon und in Kenia aus einer vergleichenden Perspektive
No full textTransitional Justice (TJ) has expanded beyond its original framework from the late 1980s, when it was centred on transitions to democracy, becoming a global norm inserted in varied contexts, especially since the establishment of the International Criminal Court (ICC) – the symbol of its normalisation. The localisation of TJ in a contemporary context comes with an increasingly common scenario of political instability and violence within electoral democracies. Taking case studies as a research strategy, this thesis first explores the exemplary events of political violence in Lebanon (the politically motivated assassination of Rafik Hariri in 2005) and Kenya (the 2007/2008 post-electoral violence), which were followed by TJ in the form of international criminal justice: the Special Tribunal for Lebanon and the International Criminal Court. The two countries, although very different, can be classified as conflicted democracies, which characteristics provide valuable insights concerning TJ in plural societies. Through a comparative perspective, this thesis analyses how TJ shapes political dynamics within conflicted democracies and the effects of those dynamics on the political stability.Transitional Justice (TJ) hat sich über seinen ursprünglichen Rahmen aus den späten 1980er Jahren hinaus ausgeweitet, als es sich auf den “Transitions to Democracy” konzentrierte. Sie wurde zu einer globalen Norm, die in verschiedenen Kontexten eingefügt wurde, insbesondere seit der Einrichtung des Internationalen Strafgerichtshofs (ICC) – dem Symbol von seiner Normalisierung. Immer häufiger geht die Lokalisierung von TJ in einen zeitgenössischen Kontext mit politischer Instabilität und politische Gewalt innerhalb von Wahldemokratien einher. Unter Verwendung von Fallstudien als Forschungsstrategie untersucht die Arbeit zunächst die beispielhaften Ereignisse politischer Gewalt im Libanon (die politisch motivierte Ermordung von Rafik Hariri im Jahr 2005) und in Kenia (die Gewalt nach den Wahlen 2007/2008), auf die TJ in Form von internationaler Strafgerichtsbarkeit folgte, zum einen durch den Sondergerichtshof für den Libanon und des Weiteren durch den Internationalen Strafgerichtshof. Obwohl die beiden Länder sehr unterschiedlich sind, können sie als “Conflicted Democracies” klassifiziert werden, deren Merkmale wertvolle Einblicke in Bezug auf TJ in pluralen Gesellschaften liefern. Durch eine vergleichende Perspektive analysiert die Dissertation, wie TJ die politische Dynamik innerhalb von “Conflicted Democracies” formt, und welche Auswirkungen diese Dynamik auf die politische Stabilität hat
Structural reflection data (.mtz) of soaked Sudan virus VP40 crystals
No full textThis repository contains structural data (.mtz) of Sudan virus VP40 crystals, soaked with small molecules. Files are ordered names correspond to internal lab crystal IDs (e.g. XDS_ASCII_AW61_scaled1.mtz, with "AWxxx" indicating the crystal ID). The resolution and data quality indicators for each dataset are provided in an accompanying metadata file. Users should refer to this file to select appropriate datasets for their analyses.
Dimeric VP40 (approx. 7 mg/ml in 25 mM Tris, 300 mM NaCl, pH 8) was mixed 1:1 with crystallization buffer (100 mM HEPES, 40 mM MgCl2, 10% v/v PEG400). Crystals grew overnight at 18 °C using the hanging drop method. Fragments originating from the FragXtal Screen (Jena Biosciences) were dissolved in DMSO to 1 M and diluted 1:10 in crystallization buffer (with or without 20% ethylene glycol as a cryoprotectant) to a final concentration of 100 mM. Crystals were then placed in a drop of the diluted fragments and soaked for either only seconds, minutes, 1 h, or overnight. Crystals were then harvested, flash-frozen in liquid nitrogen and analyzed at the Swiss Light Source, Paul-Scherrer Institute, Villigen, Switzerland (SLS BEAMLINE X06SA, DECTRIS EIGER X 16M detector, single wavelength, data collection temperature 100 K). Datasets were collected and processed using XDS and scaled using the ccp4i suite Aimless.
Mtz-files can be used for molecular replacement (using PDB-ID 8B3X or other structures of VP40 as template).
To use these mtz files for molecular replacement:
1) Download the desired mtz file(s) and the accompanying metadata.
2) Initial Structure Solution:
a. Use molecular replacement with programs such as Phaser or MOLREP from the CCP4 suite.
b. Use PDB-ID 8B3X as the initial search model. Other VP40 structures may also be suitable.
3) Rapid Initial Model Building and Refinement:
a. Use DIMPLE (Difference Map Pipeline) for quick initial refinement and map calculation.
b. Run DIMPLE.
c. This will produce refined models and maps for each dataset, suitable for initial analysis or as input for PanDDA.
4) Fragment Identification:
a. For datasets suspected to contain bound fragments, use PanDDA (Pan-Dataset Density Analysis).
b. Prepare input files as per PanDDA documentation, using DIMPLE output.
c. Run PanDDA with appropriate parameters.
d. Examine PanDDA event maps for evidence of bound fragments.
5) Model Building and Refinement:
a. Build fragments into positive difference density or PanDDA event maps.
b. Refine structures using programs like REFMAC5 or phenix.refine.
Related datasets deposited to the Protein data bank (https://www.rcsb.org/) include 8B2U (Crystal structure of SUDV VP40 in complex with salicylic acid) and 8B1S (Co-crystal of SUDV VP40 with salicylic acid).
This work was funded by the LOEWE Center DRUID (State of Hesse, Germany), project A1.
For any questions regarding the use of these datasets or analysis methods, please contact the depositing authors Stephan Becker or Anke-Dorothee Werner at the insitutte for Virology, Marburg, Germany (https://www.uni-marburg.de/en/fb20/departments/ciii/virology).LOEWE Center DRUI
Patterns of Foreign Direct Investment in Egypt— Descriptive Insights from a Novel Panel Dataset at the overnorate Level
No full textThis paper describes the main characteristics of Foreign Direct Investment (FDI) in Egypt using an unpublished dataset for FDI in 27 Egyptian governorates covering the period 1972–2009. Special attention is given to the geographical distribution of FDI, both at an aggregate and at the sectoral level. The paper is the first article of a larger empirical project on FDI in Egypt at the governorate level. Our dataset shows that FDI is unevenly distributed across Egyptian governorates. More than 60% of ‘non-petroleum greenfield FDI’ stock has been accumulated by two governorates, Cairo and Giza, and roughly 90% of FDI stock targets only 10 governorates. Tracing two spatial concentration indices of FDI inflows (Gini coefficient and coefficient of variation) over four decades, we find that the unequal geographical distribution of FDI decreased until the mid/late 1990s. This trend, however, did not continue when there was a substantial increase of FDI inflows in the 2000s. Moreover, we find differences in the degree of geographical concentration of FDI between various economic sectors. Service FDI shows the strongest concentration (mostly articulated in the ICT and finance sectors), while manufacturing FDI is the most geographically dispersed
Untersuchung der Rolle des mitochondrialen ABC-Transporters ABCB7 bei der Biosynthese von Häm- und Eisen-Schwefel-Proteinen
No full textMutations in the gene encoding the human mitochondrial transporter ABCB7 have been associated with X-linked sideroblastic anemia and cerebellar ataxia and refractory anemia with ring sideroblasts. ABCB7 is located in the mitochondrial inner membrane and considered to serve as an exporter of sulfur-containing compounds crucial for cytosolic and nuclear iron-sulfur protein biogenesis. While a few previous studies have also demonstrated a deficiency in heme-containing proteins in ABCB7-depleted cells, the precise molecular mechanisms behind these observations remain ill-defined. Various cytosolic-nuclear iron-sulfur proteins play pivotal roles in cellular iron and heme metabolism, and consequently could explain the X-linked sideroblastic anemia and cerebellar ataxia or refractory anemia with ring sideroblasts-related patient phenotypes. Other studies have suggested physical as well as functional interactions between ABCB7 and ferrochelatase, an enzyme associated with the matrix side of the mitochondrial inner membrane and mediating the final step in heme biosynthesis by inserting iron into protoporphyrin IX. These observations raised the question of a direct involvement of ABCB7 in both heme synthesis and mitochondrial heme export with possible consequences for erythropoiesis. This study aimed to assess the role of ABCB7 in hemoprotein maturation in human cells. To examine a potential mitochondrial heme export function of ABCB7, a HeLa tissue culture system overexpressing the peroxisomal heme-containing enzyme catalase was established. Using this system, RNA interference was applied to deplete ABCB7, and the consequences for both heme formation and mitochondrial export were compared to those of a ferrochelatase deficiency by using a combination of cell fractionation, enzymatic activity and immunoblotting assays. In addition, the maturation of selected mitochondrial and cytosolic-nuclear iron-sulfur proteins were assessed to study the requirement of ABCB7 in iron-sulfur protein biosynthesis. Upon depletion of either ABCB7 or ferrochelatase, the HeLa cell yield declined markedly, highlighting the indispensable nature of both ABCB7 and ferrochelatase for cell viability. Knockdown of ferrochelatase specifically affected the stability and function of hemoproteins both within and outside mitochondria, including respiratory chain complex II, cytochrome c1 of respiratory chain complex III, respiratory chain complex IV and catalase. In contrast, deficiency of ABCB7 did not significantly impair catalase activity, clearly indicating that ABCB7 does not play a role in heme export from mitochondria and the subsequent maturation of extramitochondrial hemoproteins. Moreover, the present study did not identify a general requirement of ABCB7 for mitochondrial heme proteins, arguing against a functional influence of the transporter on heme formation by ferrochelatase. Rather, loss of ABCB7 led to a compromised maturation of cytosolic and nuclear Fe/S proteins including GPAT, DPYD and NTHL1, three enzymes involved in nucleotide metabolism and DNA repair, and iron-regulatory protein 1. Plasmid-based expression of RNA interference-resistant ABCB7 reverted these effects. Together, the results corroborated earlier findings which had indicated the requirement of ABCB7 for cytosolic and nuclear iron-sulfur cluster biosynthesis. In agreement with an ABCB7 function in maturation of iron-regulatory protein 1, ABCB7 deficiency also influenced the levels of two iron regulatory protein-regulated key proteins of cellular Fe homeostasis, the iron storage protein ferritin and the iron uptake component transferrin receptor, resulting in a cellular iron deficiency phenotype. Consistently, ABCB7 deficiency triggered an increase in iron-regulatory protein 2 levels, an effect indicating decreased iron levels in the cytosolic compartment. Moreover, RNA interference-mediated depletion of ABCB7 elicited defects in mitochondrial iron-sulfur proteins, likely caused by the altered iron metabolism. Taken together, the current investigation clearly refutes critical roles of human ABCB7 in both mitochondrial heme synthesis and heme export to the cytosol and thus contradicts a direct involvement of ABCB7 in erythropoiesis. In accordance with previous studies on ABCB7 orthologs from multiple model organisms, this transporter was found to be required for the biogenesis of cytosolic-nuclear iron-sulfur proteins. The exact substrate of the transporter remains unclear and thus will be an exciting subject of future cell biological research. The concomitant, yet weaker effects on mitochondrial iron-sulfur proteins were likely caused by the oxidative stress resulting from the iron accumulation observed in ABCB7-deficient cells. The results of the present study may explain the mitochondrial phenotypes of X-linked sideroblastic anemia and cerebellar ataxia and refractory anemia with ring sideroblasts. Similar pathological mechanisms may be effective in other iron-overload diseases such as Friedreich's ataxia (caused by frataxin deficiency) and sideroblastic anemia 3 (caused by GLRX5 deficiency). Other cellular processes involving cytosolic-nuclear iron-sulfur proteins, such as iron metabolism, genome integrity and protein biosynthesis, are also affected in the case of ABCB7 deficiency, and contribute to the complex phenotype of patients who suffer from X-linked sideroblastic anemia and cerebellar ataxia or refractory anemia with ring sideroblasts.Mutationen im Gen, das für den menschlichen mitochondrialen Transporter ABCB7 kodiert, stehen in Zusammenhang mit den Krankheiten X-chromosomale sideroblastische Anämie mit zerebellärer Ataxie sowie refraktäre Anämie mit Ringsideroblasten. ABCB7 ist in der inneren Mitochondrienmembran lokalisiert und gilt als Exporteur von schwefelhaltigen Verbindungen, die für die zytosolische und nukleäre Eisen-Schwefel-Proteinbiogenese entscheidend sind. Ebenfalls haben einige frühere Studien in ABCB7-depletierten Zellen auch einen Mangel an hämhaltigen Proteinen nachgewiesen. Die genauen molekularen Mechanismen, die dieser Beobachtung zugrunde liegen, sind nach wie vor unklar. Diese Beobachtungen warfen die Frage nach einer direkten Beteiligung von ABCB7 sowohl an der Hämbiosynthese als auch am mitochondrialen Hämexport auf, mit möglichen Konsequenzen für die Erythropoese. Zusätzlich dazu könnten verschiedene zytosolisch-nukleäre Eisen-Schwefel-Proteine, die eine zentrale Rolle im zellulären Eisen- und Hämstoffwechsel spielen, die assoziierten Phänotypen der Patienten erklären. Andere Studien deuten auf physikalische und funktionelle Wechselwirkungen zwischen ABCB7 und der Ferrochelatase hin, einem Enzym, das mit der Matrixseite der inneren Mitochondrienmembran assoziiert ist und den letzten Schritt der Hämbiosynthese vermittelt. Ziel der vorliegenden Studie war es, die Rolle von ABCB7 bei der Reifung von Hämoproteinen in menschlichen Zellen zu charakterisieren. Um eine mögliche mitochondriale Hämexportfunktion von ABCB7 zu untersuchen, wurde ein HeLa-Zellkultursystem etabliert, in dem das peroxisomale, hämhaltige Enzym Katalase überexprimiert wurde. In diesem System wurde ABCB7 mittels RNA-Interferenz depletiert. Über die Messung von Enzymaktivitäten und Immunoblotting an mitochondrialen und zytosolischen Zellfraktionen wurden Effekte auf die Bildung und den mitochondrialen Export von Häm ermittelt. Diese wurden mit einem analogen Zellsystem verglichen, in dem die für die Hämbiosynthese essenzielle Ferrochelatase mittels RNA-Interferenz depletiert wurde. Darüber hinaus wurde die Synthese ausgewählter mitochondrialer sowie zytosolischer und nukleärer Eisen-Schwefel-Proteine untersucht, um die Rolle von ABCB7 in der Eisen-Schwefel-Proteinbiosynthese zu ermitteln. Nach Depletion von ABCB7 oder Ferrochelatase ging die erreichte Zellzahl deutlich zurück, was die Bedeutung sowohl von ABCB7 als auch der Ferrochelatase für Wachstum und Zellteilung zeigte. Die Depletion der Ferrochelatase wirkte sich speziell auf die Stabilität und Funktion von Hämoproteinen innerhalb und außerhalb der Mitochondrien aus, darunter der Atmungskettenkomplex II, das Cytochrom c1 des Atmungskettenkomplexes III, der Atmungskettenkomplex IV und Katalase. Im Gegensatz dazu beeinträchtigte ein Mangel an ABCB7 die Stabilität und Funktion von Hämoproteinen wie die Katalase-Aktivität nicht signifikant, was eindeutig darauf hindeutete, dass ABCB7 keine Rolle beim Hämexport aus den Mitochondrien und der anschließenden Reifung von extramitochondrialen Hämoproteinen spielt. Darüber hinaus konnte in der vorliegenden Studie keine Rolle von ABCB7 für mitochondriale Hämproteine identifiziert werden, was gegen einen funktionellen Einfluss des Transporters auf die Hämbildung durch Ferrochelatase spricht. Vielmehr führte der Verlust von ABCB7 zu einer beeinträchtigten Reifung von zytosolischen und nukleären Eisen-Schwefel-Proteinen, darunter GPAT, DPYD und NTHL1, drei Enzyme, die am Nukleotidstoffwechsel und an der DNA-Reparatur beteiligt sind, sowie des iron-regulatory proteins 1. Insgesamt bestätigten die Ergebnisse frühere Befunde, die auf die Notwendigkeit von ABCB7 für die zytosolische und nukleäre Eisen-Schwefel-Clusterbiosynthese hingewiesen hatten. Der ABCB7-Mangel beeinflusste auch die Spiegel zweier Proteine der zellulären Eisen-Homöostase, des Eisenspeicherproteins Ferritin und des Transferrinrezeptors, was zum Phänotyp eines zellulären Eisenmangels führte. Der ABCB7-Mangel führte zusätzlich zu einem Anstieg eines Markers für eine erhöhte mitochondriale Eisenaufnahme auf Kosten des zytosolischen Kompartiments. Darüber hinaus führte die RNA-Interferenz-vermittelte Depletion von ABCB7 zu Defekten bei mitochondrialen Eisen-Schwefel-Proteinen, die mutmaßlich durch den veränderten Eisenstoffwechsel verursacht wurden. Insgesamt widerlegte die aktuelle Untersuchung eindeutig eine Rolle des humanen ABCB7 sowohl bei der mitochondrialen Hämsynthese als auch beim Hämexport in das Zytosol. Die direkte Beteiligung von ABCB7 an der Erythropoese scheint somit fragwürdig. In Übereinstimmung mit früheren Studien über ABCB7-Orthologa aus mehreren Modellorganismen wurde festgestellt, dass ABCB7 für die Biogenese von zytosolisch-nukleären Eisen-Schwefel-Proteinen unabdingbar ist. Zelluläre Prozesse, an denen diese Eisen-Schwefel-Proteine beteiligt sind, wie der Eisenstoffwechsel, die Genomintegrität und die Proteinbiosynthese, sind bei ABCB7-Mangel ebenfalls betroffen. Sie tragen zum komplexen Phänotyp von Patienten mit X-chromosomaler sideroblastischer Anämie mit zerebellärer Ataxie sowie refraktärer Anämie mit Ringsideroblasten bei. Die gleichzeitigen, jedoch schwächer ausgeprägten Auswirkungen eines ABCB7-Mangels auf mitochondriale Eisen-Schwefel-Proteine wurden möglicherweise durch oxidativen Stress verursacht, der aus einer in ABCB7-defizienten Zellen beobachteten Eisenakkumulation resultierte. Ähnliche pathologische Mechanismen könnten auch bei anderen Krankheiten mit Eisenüberladung wie der Friedreich-Ataxie (verursacht durch Frataxin-Mangel) und der sideroblastischen Anämie 3 (verursacht durch GLRX5-Mangel) wirksam sein