1,720,959 research outputs found
GTP-Dependent FlhF Homodimer Supports Secretion of a Hemolysin in Bacillus cereus
Full text linkThe multidomain (B-NG) protein FlhF, a flagellar biogenesis regulator in several bacteria, is the third paralog of the signal recognition particle (SRP)-GTPases Ffh and FtsY, which are known to drive protein-delivery to the plasma membrane. Previously, we showed that FlhF is required for Bacillus cereus pathogenicity in an insect model of infection, being essential for physiological peritrichous flagellation, for motility, and for the secretion of virulence proteins. Among these proteins, we found that the L2 component of hemolysin BL, one of the most powerful toxins B. cereus produces, was drastically reduced by the FlhF depletion. Herein, we demonstrate that B. cereus FlhF forms GTP-dependent homodimers in vivo since the replacement of residues critical for their GTP-dependent homodimerization alters this ability. The protein directly or indirectly controls flagellation by affecting flagellin-gene transcription and its overproduction leads to a hyperflagellated phenotype. On the other hand, FlhF does not affect the expression of the L2-encoding gene (hblC), but physically binds L2 when in its homodimeric form, recruiting the protein to the plasma membrane for secretion. We additionally show that FlhF overproduction increases L2 secretion and that the FlhF/L2 interaction requires the NG domain of FlhF. Our findings demonstrate the peculiar behavior of B. cereus FlhF, which is required for the correct flagellar pattern and acts as SRP-GTPase in the secretion of a bacterial toxin subunit
Strukturelle und funktionelle Studien zur transkriptionellen Regulation von flagellarer Motilität und Biofilmbildung
No full textPart 1: Numerical regulation in the monotrichous bacterium Shewanella putrefaciens
Microorganisms have the ability to adapt to changing environmental conditinos. This has enabled them to colonize virtually nearly every niche on the planet Earth. Key to this ability is bacterial motility, which allows bacteria to move away from unfavourable conditions and to move towards favourable conditions. In connection with a sensory system, which detects chemical cues and other stimuli, bacteria can move towards nutrients. Bacterial motility is largely enabled by flagella. The biogenesis of a flagellum is a very costly process, which is for this reason highly regulated. In the monotrichous bacterium Shewanella putrefaciens, FlhF and FlhG are responsible for maintaining number and location of the single polar flagellum. In the course of this work, it could be shown that FlhG limits the number of flagella to one by directly interacting with the master transcriptional regulator of the flagellum, FlrA. Furthermore, FlhG is implicated in assembly of the cytosolic face of the flagellum, the C-Ring. The transcriptional control via FlrA as well as the C-Ring assembly via FliM occur through the same binding site on FlhG. This highlights the central role of FlhG and shows that FlhG integrates the two processes to regulate flagellar number. Taken together, these observations represent an important step towards a complete conceptual description of flagellar biogenesis. Thereby, these results also form the basis for further research.
Part 2: Transcriptional regulation of biofilms is mediated by RemA, which interacts with DNA in a histone-like manner
Instead of a motile lifestyle, bacteria can also establish a multicellular, sessile lifestyle in the form of biofilms. In biofilms, bacterial cells establish a division of labour and establish an increased resistance against antibiotics and environmental hazardous conditions. This is mediated by the secretion of extracellular proteins and other biological molecules. The protein RemA is central to this process, as it activates the secretion of these extracellular components. Furthermore, RemA is implicated in processes which enable a cellular protection against osmotic pressure, which occurs during biofilm formation. In the context of this work, the structure of RemA from Geobacillus thermodenitrificans could be elucidated. RemA interacts with DNA in a novel and unique way, which is reminiscent of DNA-looping by histone-complexes. By means of biochemical methods, crucial residues of RemA responsible for DNA interaction could be functionally investigated. Furthermore, the structural fate of amino acid mutations, which impair the functionality of RemA, could be investigated. Taken together, this work represents an important step towards the understanding of the transcriptional processes that govern biofilm-formation and osmoprotection in Bacillus subtilis. This work also provides the basis to further investigate the function of RemA in the cellular context. In the future, the structural investigation of RemA-DNA-interaction is facilitated by the insights obtained in the context of this work.
Part 3: Membrane protein biogenesis is regulated by a structurally unique, co-translational state of FtsY.
Membrane proteins are translated by ribosomes and predominantly inserted into the membrane by the SecYEG-translocon. A factor critical for this process is the SRP-receptor FtsY, which enables co-translational targeting to the translocon in coopration with the SRP-particle FFH and SRP-RNA. In the context of this work it could be shown that a co-translational state of FtsY, the helical domain N2-4, critically mediates membrane targeting of the receptor. By means of crystallographic analyses and studies in solution, it could be shown that the subdomain of N2-4 possesses a different fold when isolated than in the context of the G-domain of FtsY. This observation represents a unique paradigm, which indicates that nascent N2-4 executes a different function during its own translation than when N2-4 is part of the mature FtsY-receptor. These results are an important step towards the conceptual understanding of membrane protein biogenesis and –targeting. Further work could elucidate, whether this concept also applies to homologs of FtsY such as FlhF.Teil 1: Numerische Regulierung im monotrichen Bakterium Shewanella putrefaciens
Die Fähigkeit von Mikroorganismen, sich an wechselnde Umgebungen anzupassen, hat dazu geführt, dass Bakterien beinahe jede Nische des Planeten Erde besiedelt haben. Eine Schlüsselfähigkeit für das Überleben von Bakterien stellt die Motilität dar. Diese erlaubt Bakterien, bevorzugte Lebensumgebungen anzusteuern und solche Umgebungen, die für das Überleben nicht förderlich sind, zu verlassen. In Verbindung mit einem Sensorium, durch das Bakterien Nährstoffe und andere Parameter wahrnehmen können, ermöglicht die Motilität den Bakterien die Bewegung in Richtung von Nährstoffgradienten. Bakterielle Motilität wird großmehrheitlich durch Flagellen ermöglicht. Die Biogenese eines Flagellums ist für die Zelle ein sehr kostspieliger Prozess. Dementsprechend ist die Flagellen-Biogenese hochgradig reguliert. In dem monotrich flagellierten Bakterium Shewanella putrefaciens sind die Proteine FlhF und FlhG verantwortlich für die Etablierung des flagellaren Musters. Im Rahmen dieser Arbeit konnte gezeigt werden, dass FlhG die Anzahl der Flagellen auf eins reguliert, indem es direkt mit dem Master-Regulator der flagellaren Biogenese, FlrA, interagiert. FlhG ist darüberhinaus am Zusammenbau des cytoplasmatischen Teils des Flagellums, dem C-Ring, beteiligt. Transkriptionelle Kontrolle via FlrA sowie die C-Ring-Assemblierung via FliM werden durch dieselbe Bindestelle an FlhG gesteuert. Dies macht deutlich, dass FlhG eine bisher unerkannte Schlüsselrolle spielt und den Prozess der Flagellen-Biogenese mit der transkriptionellen Regulierung integriert. Zusammen genommen bilden diese Erkenntnisse einen wichtigen Schritt in Richtung einer vollständigen Beschreibung der Flagellenbiogenese und der numerischen Regulierung derselben. Damit bilden die Einblicke auch die Basis für weitere Untersuchungen.
Teil 2: Transkriptionelle Regulierung von Biofilmen geschieht durch RemA, welches histon-artig mit DNA interagiert
Anstelle der motilen Lebensart sind viele Bakterien in der Lage, in einem gesellschaftlichen Lebensstil zu existieren in Form von Biofilmen. Biofilme sind mehrzellige Gruppierungen von bakteriellen Zellen, in welchen Aufgabenteilung stattfindet und die eine erhöhte Resistenz gegenüber Antibiotika und Umwelteinflüssen bieten. Dies wird massgeblich bewerkstelligt durch die Sekretion von extrazellulären Proteinen und anderen Biomolekülen. RemA ist ein zentrales Protein während dieses Prozesses, welches die Sekretion von diesen extrazellulären Bausteinen transkriptionell aktiviert. Darüber hinaus aktiviert RemA Schutzprozesse der Zelle, um hohen Salinitäten entgegenzusteuern, die sich bei der Biofilm-Bildung zwangsläufig ergeben. Im Rahmen dieser Arbeit konnte die Struktur von RemA aus Geobacillus thermodenitrificans aufgeklärt werden. Die Struktur von RemA zeigt eine gänzlich neue Form der DNA-Interaktion, die an das DNA-Looping von Histon-Komplexen erinnert. Mittels biochemischer Methoden konnte die Art und Weise eruiert werden, wie RemA DNA bindet, und es konnten die strukturellen Auswirkungen der Mutation von funktionell wichtige Aminosäuren identifiziert werden. Damit bilden die hier gewonnenen Erkenntnisse eine wichtige Grundlage, um die Funktion von RemA im zellulären Kontext zu verstehen. Gleichzeitig ermöglicht diese Arbeit weiterreichende Untersuchungen, um RemA gemeinschaftlich mit DNA strukturell aufzuklären und weitere Proteine zu identifizieren, die RemA ähnlich sind.
Teil 3: Membranprotein-Biogenese wird durch einen co-translationellen Zustand von FtsY gesteuert.
Membranproteine werden durch Ribosomen translatiert und großmehrheitlich co-translational durch das SecYEG-Translocon in die Plasmamembran insertiert. Ein wichtiger Faktor beim co-translationalen Einbau von Membranproteinen in die Membran spielt der SRP-Rezeptor FtsY, welcher zusammen mit dem SRP-Partikel FFH und SRP-RNA die Zielführung von Ribosomen zum SecYEG-Translocon ermöglicht. Im Rahmen dieser Arbeit konnte gezeigt werden, dass ein co-translationaler Zustand von FtsY, die helikale Domäne N2-4, massgeblich zur Zielsteuerung zur Membran beiträgt. Durch kristallographische Studien und Untersuchungen in Lösung konnte gezeigt werden, dass die Subdomäne N2-4 isoliert eine andere Faltung zeigt als im Kontext der G-Domäne von FtsY. Diese Beobachtung stellt ein Novum dar, denn die strukturelle Bi-stabilität von N2-4 geht offenbar einher mit dedizierten Funktionen. Diese Erkenntnisse stellen somit einen wichtigen Baustein dar im Feld der Membranprotein-Biogenese. Die Arbeiten dienen auch als Basis für weitergehende Untersuchungen, ob solch ein strukturell bimodaler Zustand bei Homologen von FtsY (etwa FlhF) oder anderen Proteinen ebenfalls auftritt
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Structural and functional studies on the transcriptional regulation of flagellar motility and biofilm formation
Full text linkPart 1: Numerical regulation in the monotrichous bacterium Shewanella putrefaciens
Microorganisms have the ability to adapt to changing environmental conditinos. This has enabled them to colonize virtually nearly every niche on the planet Earth. Key to this ability is bacterial motility, which allows bacteria to move away from unfavourable conditions and to move towards favourable conditions. In connection with a sensory system, which detects chemical cues and other stimuli, bacteria can move towards nutrients. Bacterial motility is largely enabled by flagella. The biogenesis of a flagellum is a very costly process, which is for this reason highly regulated. In the monotrichous bacterium Shewanella putrefaciens, FlhF and FlhG are responsible for maintaining number and location of the single polar flagellum. In the course of this work, it could be shown that FlhG limits the number of flagella to one by directly interacting with the master transcriptional regulator of the flagellum, FlrA. Furthermore, FlhG is implicated in assembly of the cytosolic face of the flagellum, the C-Ring. The transcriptional control via FlrA as well as the C-Ring assembly via FliM occur through the same binding site on FlhG. This highlights the central role of FlhG and shows that FlhG integrates the two processes to regulate flagellar number. Taken together, these observations represent an important step towards a complete conceptual description of flagellar biogenesis. Thereby, these results also form the basis for further research.
Part 2: Transcriptional regulation of biofilms is mediated by RemA, which interacts with DNA in a histone-like manner
Instead of a motile lifestyle, bacteria can also establish a multicellular, sessile lifestyle in the form of biofilms. In biofilms, bacterial cells establish a division of labour and establish an increased resistance against antibiotics and environmental hazardous conditions. This is mediated by the secretion of extracellular proteins and other biological molecules. The protein RemA is central to this process, as it activates the secretion of these extracellular components. Furthermore, RemA is implicated in processes which enable a cellular protection against osmotic pressure, which occurs during biofilm formation. In the context of this work, the structure of RemA from Geobacillus thermodenitrificans could be elucidated. RemA interacts with DNA in a novel and unique way, which is reminiscent of DNA-looping by histone-complexes. By means of biochemical methods, crucial residues of RemA responsible for DNA interaction could be functionally investigated. Furthermore, the structural fate of amino acid mutations, which impair the functionality of RemA, could be investigated. Taken together, this work represents an important step towards the understanding of the transcriptional processes that govern biofilm-formation and osmoprotection in Bacillus subtilis. This work also provides the basis to further investigate the function of RemA in the cellular context. In the future, the structural investigation of RemA-DNA-interaction is facilitated by the insights obtained in the context of this work.
Part 3: Membrane protein biogenesis is regulated by a structurally unique, co-translational state of FtsY.
Membrane proteins are translated by ribosomes and predominantly inserted into the membrane by the SecYEG-translocon. A factor critical for this process is the SRP-receptor FtsY, which enables co-translational targeting to the translocon in coopration with the SRP-particle FFH and SRP-RNA. In the context of this work it could be shown that a co-translational state of FtsY, the helical domain N2-4, critically mediates membrane targeting of the receptor. By means of crystallographic analyses and studies in solution, it could be shown that the subdomain of N2-4 possesses a different fold when isolated than in the context of the G-domain of FtsY. This observation represents a unique paradigm, which indicates that nascent N2-4 executes a different function during its own translation than when N2-4 is part of the mature FtsY-receptor. These results are an important step towards the conceptual understanding of membrane protein biogenesis and –targeting. Further work could elucidate, whether this concept also applies to homologs of FtsY such as FlhF
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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