@phdthesis{Feineis2018, author = {Feineis, Susanne}, title = {Thioether-poly(glycidol) as multifunctional coating system for gold nanoparticles}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172902}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {The aim of this thesis was the development of a multifunctional coating system for AuNPs based on thioether polymers, providing both excellent colloidal stability and a variable possibility to introduce functionalities for biological applications. First, two thioether-polymer systems were synthesised as a systematic investigation into colloidal stabilisation efficacy. Besides commonly used monovalent poly(ethylene glycol) (PEG-SR), its structural analogue linear poly(glycidol) (PG-SR) bearing multiple statistically distributed thioether moieties along the backbone was synthesised. Additionally, respective thiol analogues (PEG-SH and PG-SH) were produced and applied as reference. Successive modification of varyingly large AuNPs with aforementioned thiol- and thioether-polymers was performed via ligand exchange reaction on citrate stabilised AuNPs. An increased stabilisation efficacy of both thioether-polymers against biological and physiological conditions, as well as against freeze-drying compared to thiol analogues was determined. Based on the excellent colloidal stabilisation efficacy and multi-functionalisability of thioether-PG, a plethora of functional groups, such as charged groups, hydrophilic/hydrophobic chains, as well as bio-active moieties namely diazirine and biotin was introduced to the AuNP surface. Moreover, the generic and covalent binding of diazirine-modified PG-SR with biomolecules including peptides and proteins was thoroughly demonstrated. Lastly, diverse applicability and bioactivity of aforementioned modified particles in various studies was displayed, once more verifying the introduction of functionalities. On the one hand the electrostatic interaction of charged AuNPs with hydrogels based on hyaluronic acid was applied to tune the release kinetics of particles from three-dimensional scaffolds. On the other hand the strong complexation of siRNA onto two positively charged AuNPs was proven. The amount of siRNA payload was tuneable by varying the surface charge, ionic strength of the surrounding medium and the N/P ratio. Moreover, the biological activity and selectivity of the biotin-streptavidin conjugation was verified with respectively functionalised particles in controlled agglomeration test and in laser-triggered cell elimination experiments. In the latter, streptavidin-functionalised AuNPs resulted in excellent depletion of biotinylated cells whereas unfunctionalised control particles failed, excluding unspecific binding of these particles to the cell surface.}, subject = {Nanopartikel}, language = {en} } @article{RiquelmeHaarerKammleretal.2018, author = {Riquelme, Paloma and Haarer, Jan and Kammler, Anja and Walter, Lisa and Tomiuk, Stefan and Ahrens, Norbert and Wege, Anja K. and Goecze, Ivan and Zecher, Daniel and Banas, Bernhard and Spang, Rainer and F{\"a}ndrich, Fred and Lutz, Manfred B. and Sawitzki, Birgit and Schlitt, Hans J. and Ochando, Jordi and Geissler, Edward K. and Hutchinson, James A.}, title = {TIGIT\(^+\) iTregs elicited by human regulatory macrophages control T cell immunity}, series = {Nature Communications}, volume = {9}, journal = {Nature Communications}, number = {9}, doi = {10.1038/s41467-018-05167-8}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-226321}, pages = {2858, 1-18}, year = {2018}, abstract = {Human regulatory macrophages (Mreg) have shown early clinical promise as a cell-based adjunct immunosuppressive therapy in solid organ transplantation. It is hypothesised that recipient CD4(+) T cell responses are actively regulated through direct allorecognition of donor-derived Mregs. Here we show that human Mregs convert allogeneic CD4(+) T cells to IL-10-producing, TIGIT(+) FoxP3(+)-induced regulatory T cells that non-specifically suppress bystander T cells and inhibit dendritic cell maturation. Differentiation of Mreg-induced Tregs relies on multiple non-redundant mechanisms that are not exclusive to interaction of Mregs and T cells, including signals mediated by indoleamine 2,3-dioxygenase, TGF-beta, retinoic acid, Notch and progestagen-associated endometrial protein. Preoperative administration of donor-derived Mregs to living-donor kidney transplant recipients results in an acute increase in circulating TIGIT(+) Tregs. These results suggest a feed-forward mechanism by which Mreg treatment promotes allograft acceptance through rapid induction of direct-pathway Tregs.}, language = {en} } @phdthesis{Nuernberger2018, author = {N{\"u}rnberger, Fabian}, title = {Timing of colony phenology and foraging activity in honey bees}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-155105}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {I. Timing is a crucial feature in organisms that live within a variable and changing environment. Complex mechanisms to measure time are wide-spread and were shown to exist in many taxa. These mechanisms are expected to provide fitness benefits by enabling organisms to anticipate environmental changes and adapt accordingly. However, very few studies have addressed the adaptive value of proper timing. The objective of this PhD-project was to investigate mechanisms and fitness consequences of timing decisions concerning colony phenology and foraging activity in the honey bee (Apis mellifera), a social insect species with a high degree of social organization and one of the most important pollinators of wild plants and crops. In chapter II, a study is presented that aimed to identify the consequences of disrupted synchrony between colony phenology and the local environment by manipulating the timing of brood onset after hibernation. In a follow-up experiment, the importance of environmental factors for the timing of brood onset was investigated to assess the potential of climate change to disrupt synchronization of colony phenology (Chapter III). Chapter IV aimed to prove for the first time that honey bees can use interval time-place learning to improve foraging activity in a variable environment. Chapter V investigates the fitness benefits of information exchange between nest mates via waggle dance communication about a resource environment that is heterogeneous in space and time. II. In the study presented in chapter II, the importance of the timing of brood onset after hibernation as critical point in honey bee colony phenology in temperate zones was investigated. Honey bee colonies were overwintered at two climatically different sites. By translocating colonies from each site to the other in late winter, timing of brood onset was manipulated and consequently colony phenology was desynchronized with the local environment. Delaying colony phenology in respect to the local environment decreased the capability of colonies to exploit the abundant spring bloom. Early brood onset, on the other hand, increased the loads of the brood parasite Varroa destructor later in the season with negative impact on colony worker population size. This indicates a timing related trade-off and illustrates the importance of investigating effects of climate change on complex multi-trophic systems. It can be concluded that timing of brood onset in honey bees is an important fitness relevant step for colony phenology that is highly sensitive to climatic conditions in late winter. Further, phenology shifts and mismatches driven by climate change can have severe fitness consequences. III. In chapter III, I assess the importance of the environmental factors ambient temperature and photoperiod as well as elapsed time on the timing of brood onset. Twenty-four hibernating honey bee colonies were placed into environmental chambers and allocated to different combinations of two temperature regimes and three different light regimes. Brood onset was identified non-invasively by tracking comb temperature within the winter cluster. The experiment revealed that ambient temperature plays a major role in the timing of brood onset, but the response of honey bee colonies to temperature increases is modified by photoperiod. Further, the data indicate the involvement of an internal clock. I conclude that the timing of brood onset is complex but probably highly susceptible to climate change and especially spells of warm weather in winter. IV. In chapter IV, it was examined if honey bees are capable of interval time-place learning and if this ability improves foraging efficiency in a dynamic resource environment. In a field experiment with artificial feeders, foragers were able to learn time intervals and use this ability to anticipate time periods during which feeders were active. Further, interval time-place learning enabled foragers to increase nectar uptake rates. It was concluded that interval time-place learning can help honey bee foragers to adapt to the complex and variable temporal patterns of floral resource environments. V. The study presented in chapter V identified the importance of the honey bee waggle dance communication for the spatiotemporal coordination of honey bee foraging activity in resource environments that can vary from day to day. Consequences of disrupting the instructional component of honey bee dance communication were investigated in eight temperate zone landscapes with different levels of spatiotemporal complexity. While nectar uptake of colonies was not affected, waggle dance communication significantly benefitted pollen harvest irrespective of landscape complexity. I suggest that this is explained by the fact that honey bees prefer to forage pollen in semi-natural habitats, which provide diverse resource species but are sparse and presumably hard to find in intensively managed agricultural landscapes. I conclude that waggle dance communication helps to ensure a sufficient and diverse pollen diet which is crucial for honey bee colony health. VI. In my PhD-project, I could show that honey bee colonies are able to adapt their activities to a seasonally and daily changing environment, which affects resource uptake, colony development, colony health and ultimately colony fitness. Ongoing global change, however, puts timing in honey bee colonies at risk. Climate change has the potential to cause mismatches with the local resource environment. Intensivation of agricultural management with decreased resource diversity and short resource peaks in spring followed by distinctive gaps increases the probability of mismatches. Even the highly efficient foraging system of honey bees might not ensure a sufficiently diverse and healthy diet in such an environment. The global introduction of the parasitic mite V. destructor and the increased exposure to pesticides in intensively managed landscapes further degrades honey bee colony health. This might lead to reduced cognitive capabilities in workers and impact the communication and social organization in colonies, thereby undermining the ability of honey bee colonies to adapt to their environment.}, subject = {Biene}, language = {en} } @phdthesis{SchenkneeWolf2018, author = {Schenk [n{\´e}e Wolf], Mariela}, title = {Timing of wild bee emergence: mechanisms and fitness consequences}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161565}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Solitary bees in seasonal environments have to align their life-cycles with favorable environmental conditions and resources. Therefore, a proper timing of their seasonal activity is highly fitness relevant. Most species in temperate environments use temperature as a trigger for the timing of their seasonal activity. Hence, global warming can disrupt mutualistic interactions between solitary bees and plants if increasing temperatures differently change the timing of interaction partners. The objective of this dissertation was to investigate the mechanisms of timing in spring-emerging solitary bees as well as the resulting fitness consequences if temporal mismatches with their host plants should occur. In my experiments, I focused on spring-emerging solitary bees of the genus Osmia and thereby mainly on O. cornuta and O. bicornis (in one study which is presented in Chapter IV, I additionally investigated a third species: O. brevicornis). Chapter II presents a study in which I investigated different triggers solitary bees are using to time their emergence in spring. In a climate chamber experiment I investigated the relationship between overwintering temperature, body size, body weight and emergence date. In addition, I developed a simple mechanistic model that allowed me to unite my different observations in a consistent framework. In combination with the empirical data, the model strongly suggests that solitary bees follow a strategic approach and emerge at a date that is most profitable for their individual fitness expectations. I have shown that this date is on the one hand temperature dependent as warmer overwintering temperatures increase the weight loss of bees during hibernation, which then advances their optimal emergence date to an earlier time point (due to an earlier benefit from the emergence event). On the other hand I have also shown that the optimal emergence date depends on the individual body size (or body weight) as bees adjust their emergence date accordingly. My data show that it is not enough to solely investigate temperature effects on the timing of bee emergence, but that we should also consider individual body conditions of solitary bees to understand the timing of bee emergence. In Chapter III, I present a study in which I investigated how exactly temperature determines the emergence date of solitary bees. Therefore, I tested several variants degree-day models to relate temperature time series to emergence data. The basic functioning of such degree-day models is that bees are said to finally emerge when a critical amount of degree-days is accumulated. I showed that bees accumulate degree-days only above a critical temperature value (~4°C in O. cornuta and ~7°C in O. bicornis) and only after the exceedance of a critical calendar date (~10th of March in O. cornuta and ~28th of March in O. bicornis). Such a critical calendar date, before which degree-days are not accumulated irrespective of the actual temperature, is in general less commonly used and, so far, it has only been included twice in a phenology model predicting bee emergence. Furthermore, I used this model to retrospectively predict the emergence dates of bees by applying the model to long-term temperature data which have been recorded by the regional climate station in W{\"u}rzburg. By doing so, the model estimated that over the last 63 years, bees emerged approximately 4 days earlier. In Chapter IV, I present a study in which I investigated how temporal mismatches in bee-plant interactions affect the fitness of solitary bees. Therefore, I performed an experiment with large flight cages serving as mesocosms. Inside these mesocosms, I manipulated the supply of blossoms to synchronize or desynchronize bee-plant interactions. In sum, I showed that even short temporal mismatches of three and six days in bee-plant interactions (with solitary bee emergence before flower occurrence) can cause severe fitness losses in solitary bees. Nonetheless, I detected different strategies by solitary bees to counteract impacts on their fitness after temporal mismatches. However, since these strategies may result in secondary fitness costs by a changed sex ratio or increased parasitism, I concluded that compensation strategies do not fully mitigate fitness losses of bees after short temporal mismatches with their food plants. In the event of further climate warming, fitness losses after temporal mismatches may not only exacerbate bee declines but may also reduce pollination services for later-flowering species and affect populations of animal-pollinated plants. In conclusion, I showed that spring-emerging solitary bees are susceptible to climate change as in response to warmer temperatures bees advance their phenology and show a decreased fitness state. As spring-emerging solitary bees not only consider overwintering temperature but also their individual body condition for adjusting emergence dates, this may explain differing responses to climate warming within and among bee populations which may also have consequences for bee-plant interactions and the persistence of bee populations under further climate warming. If in response to climate warming plants do not shift their phenologies according to the bees, bees may experience temporal mismatches with their host plants. As bees failed to show a single compensation strategy that was entirely successful in mitigating fitness consequences after temporal mismatches with their food plants, the resulting fitness consequences for spring-emerging solitary bees would be severe. Furthermore, I showed that spring-emerging solitary bees use a critical calendar date before which they generally do not commence the summation of degree-days irrespective of the actual temperature. I therefore suggest that further studies should also include the parameter of a critical calendar date into degree-day model predictions to increase the accuracy of model predictions for emergence dates in solitary bees. Although our retrospective prediction about the advance in bee emergence corresponds to the results of several studies on phenological trends of different plant species, we suggest that more research has to be done to assess the impacts of climate warming on the synchronization in bee-plant interactions more accurately.}, subject = {wild bees}, language = {en} } @article{KlenkeQuastPrelogetal.2018, author = {Klenke, Daniela and Quast, Anja and Prelog, Martina and Holl-Wieden, Annette and Riekert, Maximilian and Stellzig-Eisenhauer, Angelika and Meyer-Marcotty, Philipp}, title = {TMJ pathomorphology in patients with JIA-radiographic parameters for early diagnosis-}, series = {Head \& Face Medicine}, volume = {14}, journal = {Head \& Face Medicine}, doi = {10.1186/s13005-018-0173-5}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-325882}, year = {2018}, abstract = {Background Juvenile idiopathic arthritis (JIA) is often accompanied by pathomorphological changes to the temporomandibular joint (TMJ). By analyzing orthodontical orthopantomograms of JIA patients the aims of the study were a) classification of condyle changes, b) quantification of bony asymmetries of condylar destruction and c) detection of relationships between disease duration and TMJ-involvement. Patients/Methods 46 caucasian JIA-patients (28 female; 18 male; < 16.0 years) were enrolled, each joint (n = 92) was morphologically assessed by means of orthopantomogram, quantitatively analysed and compared with duration of general disease. Condyle morphology was assessed using the Billiau scale for severity of destruction [1]. The quantitative analysis was based on ratios of condyle, ramus and mandible height. Results Patients were divided into groups (Group I - slightly affected, n = 36; Billiau severity 0-2; condyle findings: X-ray normal, condyle erosions, condylar flattening; Group II - severely affected, N = 10; Billiau severity 3-4; condyle findings: condylar flattenings and erosions, unilateral/bilateral complete loss of condyles), based on morphological analysis of condylar destruction. Duration of disease was significantly longer in Group II (8.9 ± 5.2 years) than in Group I (4.6 ± 4.7 years). Asymmetries of condyle, ramus and mandible height, quantitatively analysed by contralateral comparison, were significantly more marked in patients of Group II than of Group I. Conclusions Orthopantomogram imaging can be used in orthodontics clinical routine to detect TMJ-pathologies and is an important reference for monitoring progression of JIA. Classification into severe and slightly affected TMJ is possible by analysis of condylar pathomorphology. An association between degree of destruction, extent of lower jaw asymmetry and disease duration is suggested by the results.}, language = {en} } @article{VendelovaAshourBlanketal.2018, author = {Vendelova, Emilia and Ashour, Diyaaeldin and Blank, Patrick and Erhard, Florian and Saliba, Antoine-Emmanuel and Kalinke, Ulrich and Lutz, Manfred B.}, title = {Tolerogenic transcriptional signatures of steady-state and pathogen-induced dendritic cells}, series = {Frontiers in Immunology}, volume = {9}, journal = {Frontiers in Immunology}, number = {333}, doi = {10.3389/fimmu.2018.00333}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-175636}, year = {2018}, abstract = {Dendritic cells (DCs) are key directors of tolerogenic and immunogenic immune responses. During the steady state, DCs maintain T cell tolerance to self-antigens by multiple mechanisms including inducing anergy, deletion, and Treg activity. All of these mechanisms help to prevent autoimmune diseases or other hyperreactivities. Different DC subsets contribute to pathogen recognition by expression of different subsets of pattern recognition receptors, including Toll-like receptors or C-type lectins. In addition to the triggering of immune responses in infected hosts, most pathogens have evolved mechanisms for evasion of targeted responses. One such strategy is characterized by adopting the host's T cell tolerance mechanisms. Understanding these tolerogenic mechanisms is of utmost importance for therapeutic approaches to treat immune pathologies, tumors and infections. Transcriptional profiling has developed into a potent tool for DC subset identification. Here, we review and compile pathogen-induced tolerogenic transcriptional signatures from mRNA profiling data of currently available bacterial- or helminth-induced transcriptional signatures. We compare them with signatures of tolerogenic steady-state DC subtypes to identify common and divergent strategies of pathogen induced immune evasion. Candidate molecules are discussed in detail. Our analysis provides further insights into tolerogenic DC signatures and their exploitation by different pathogens.}, language = {en} } @techreport{Greubel2018, type = {Working Paper}, author = {Greubel, Johannes}, title = {Towards a Profound European Asylum System? On EU Governance during the Refugee Crisis}, edition = {1. Auflage}, issn = {2625-6193}, doi = {10.25972/OPUS-16879}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-168797}, pages = {43}, year = {2018}, abstract = {The refugee crisis has developed as one of the major challenges for EU governance in recent years. From 2013 onwards, the crisis determined the political agenda and public discourse within European politics. During that time, the numbers of asylum seekers reaching Europe increased dramatically, with more than one million people applying for asylum at the crisis peak in 2015. This paper deals with the efforts taken by the EU and its member states to mitigate and overcome the refugee crisis. How exactly has the EU reacted to the refugee crisis and how and to what extend have the EU and its governance changed throughout the crisis? These research questions are approached through a reconstructive analysis of the whole period of crisis. This approach provides for a comprehensive examination of the refugee crisis that includes all issues, measures and processes of the EU's policy reaction at the same time. It will be argued that due to severe shortcomings of the Dublin regulation and the Common European Asylum System, a crisis in the EU's refugee policy was already predestined. This was the case from 2013 onwards. The EU approached the crisis in three stages - neglect and non-solidarity leading to unilateral approaches by affected states, supranational short-term emergency measures during the peak of crisis and enhanced cooperation with third countries, especially with Turkey, the Western Balkans states and African states - until the crisis lost traction in 2017. Yet, the asylum system's shortcomings are still not eliminated as the lasting measures of the EU's crisis management between 2013 and 2018 mainly focused on border security and externalisation. EU governance changed towards more intergovernmental, informal and regional action. Further, the crisis led to serious rows between member states, leading to the fragmentation of the EU into two blocs. With decreasing numbers of asylum seeker in the last few years, what remains is an incomplete asylum system and a political crisis among member states.}, subject = {Europ{\"a}ische Union}, language = {en} } @phdthesis{Mao2018, author = {Mao, Lujia}, title = {Transition Metal-Catalyzed Construction of Benzyl/Allyl sp\(^3\) and Vinyl/Allenyl sp\(^2\) C-B Bonds}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154022}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Organoboron compounds, such as benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates, have been synthesized via metal-catalyzed borylations of sp3 C-O and C-H bonds. Thus, Cu-catalyzed borylations of alcohols and their derivatives provide benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates via nucleophilic substitution. The employment of Ti(OiPr)4 turns the OH moiety into a good leaving group ('OTi'). The products of Pd-catalyzed oxidative borylations of allylic C-H bonds of alkenes were isolated and purified, and their application in the one-pot synthesis of stereodefined homoallyl alcohols was also investigated. Chapter 2 presents a copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively, employing a commercially available catalyst precursor, [Cu(CH3CN)4]2+[BF4-]2, and Xantphos as the ligand. The borylation of benzylic alcohols was carried out at 100 oC with 5-10 mol \% [Cu(CH3CN)4]2+[BF4-]2, which afforded benzylic boronates in 32\%-95\% yields. With 10 mol \% [Cu(CH3CN)4]2+[BF4-]2, allylic boronates were provided in 53\%-89\% yields from the borylation of allylic alcohols at 60 or 100 oC. Secondary allylboronates were prepared in 72\%-84\% yields from the borylation of primary allylic alcohols, which also suggests that a nucleophilic substitution pathway is involved in this reaction. Allenylboronates were also synthesized in 72\%-89\% yields from the borylation of propargylic alcohols at 40 or 60 oC. This methodology can be extended to borylation of benzylic and allylic acetates. This protocol exhibits broad reaction scope (40 examples) and high efficiency (up to 95\% yield) under mild conditions, including the preparation of secondary allylic boronates. Preliminary mechanistic studies suggest that nucleophilic substitution is involved in this reaction. Chapter 3 reports an efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via copper-catalyzed borylation reactions under mild conditions. In the presence of a commercially available catalyst precursor (Cu(OAc)2 or Cu(acac)2) and ligand (Xantphos), the reaction affords the desired products in up to 92\% yield with a broad substrate scope (43 examples). Vinylboronates were synthesized in 50\%-83\% yields via Cu-catalyzed hydroboration of mono-substituted propargylic alcohols. With 1,1-disubstituted propargylic alcohols as the starting materials and Cu(OAc)2 as the catalyst precursor, a variety of allylboronates were synthesized in 44\%-83\% yields. The (E)-2-boryl allylboronates were synthesized in 54\%-92\% yields via the Cu-catalyzed diboration of propargylic alcohols. The stereoselectivity is different from the Pd(dba)2-catalyzed diboration of allenes that provided (Z)-2-boryl allylboronates predominantly. The isolation of an allenyl boronate as the reaction intermediate suggests that an SN2'-type reaction, followed by borylcupration, is involved in the mechanism of the diboration of propargylic alcohols. In chapter 4, a Pd-catalyzed allylic C-H borylation of alkenes is reported. The transformation exhibits high regioselectivity with a variety of linear alkenes, employing a Pd-pincer complex as the catalyst precursor, and the allylic boronate products were isolated and purified. This protocol can also be extended to one-pot carbonyl allylation reactions to provide homoallyl alcohols efficiently. An interesting mechanistic feature is that the reaction proceeds via a Pd(II)/Pd(IV) catalytic cycle. Formation of the Pd(IV) intermediate occurs by a unique combination of an NCNpincer complex and application of F-TEDA-BF4 as the oxidant. An important novelty of the present C-H borylation reaction is that all allyl-Bpin products can be isolated with usually high yields. This is probably a consequence of the application of the NCN-pincer complex as catalyst, which selectively catalyzes C-B bond formation avoiding subsequent C-B bond cleavage based side-reactions}, subject = {{\"U}bergangsmetall}, language = {en} } @phdthesis{Grauer2018, author = {Grauer, Stefan}, title = {Transport Phenomena in Bi\(_2\)Se\(_3\) and Related Compounds}, publisher = {Verlag Dr. Hut GmbH}, isbn = {978-3-8439-3481-7}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157666}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {One of the most significant technological advances in history was driven by the utilization of a new material class: semiconductors. Its most important application being the transistor, which is indispensable in our everyday life. The technological advance in the semiconductor industry, however, is about to slow down. Making transistors ever smaller to increase the performance and trying to reduce and deal with the dissipative heat will soon reach the limits dictated by quantum mechanics with Moore himself, predicting the death of his famous law in the next decade. A possible successor for semiconductor transistors is the recently discovered material class of topological insulators. A material which in its bulk is insulating but has topological protected metallic surface states or edge states at its boundary. Their electrical transport characteristics include forbidden backscattering and spin-momentum-locking with the spin of the electron being perpendicular to its momentum. Topological insulators therefore offer an opportunity for high performance devices with low dissipation, and applications in spintronic where data is stored and processed at the same point. The topological insulator Bi\(_2\)Se\(_3\) and related compounds offer relatively high energy band gaps and a rather simple band structure with a single dirac cone at the gamma point of the Brillouin zone. These characteritics make them ideal candidates to study the topological surface state in electrical transport experiments and explore its physics.}, subject = {Topologischer Isolator}, language = {en} } @article{RubioCosialsSchulzLambertsenetal.2018, author = {Rubio-Cosials, Anna and Schulz, Eike C. and Lambertsen, Lotte and Smyshlyaev, Georgy and Rojas-Cordova, Carlos and Forslund, Kristoffer and Karaca, Ezgi and Bebel, Aleksandra and Bork, Peer and Barabas, Orsolya}, title = {Transposase-DNA Complex Structures Reveal Mechanisms for Conjugative Transposition of Antibiotic Resistance}, series = {Cell}, volume = {173}, journal = {Cell}, number = {1}, doi = {10.1016/j.cell.2018.02.032}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-227085}, pages = {e20, 208-220}, year = {2018}, abstract = {Conjugative transposition drives the emergence of multidrug resistance in diverse bacterial pathogens, yet the mechanisms are poorly characterized. The Tn1549 conjugative transposon propagates resistance to the antibiotic vancomycin used for severe drug-resistant infections. Here, we present four high-resolution structures of the conserved Y-transposase of Tn1549 complexed with circular transposon DNA intermediates. The structures reveal individual transposition steps and explain how specific DNA distortion and cleavage mechanisms enable DNA strand exchange with an absolute minimum homology requirement. This appears to uniquely allow Tn916-like conjugative transposons to bypass DNA homology and insert into diverse genomic sites, expanding gene transfer. We further uncover a structural regulatory mechanism that prevents premature cleavage of the transposon DNA before a suitable target DNA is found and generate a peptide antagonist that interferes with the transposase-DNA structure to block transposition. Our results reveal mechanistic principles of conjugative transposition that could help control the spread of antibiotic resistance genes.}, language = {en} }