1,720,956 research outputs found
Controlling association of vesicle embedded peptides by alteration of the physical state of the lipid matrix
No full textWe report here the reversible association of a designed peptide embedded in a lipid membrane through a stimulus-sensitive trigger that changes the physical state of the bilayer matrix. A peptide designed with the classical 4-3 heptad repeat of coiled coils, equipped with leucine residues at all canonical interface positions, TH1, was rendered membrane soluble by replacement of all exterior residues with randomly selected hydrophobic amino acids. Insertion of TH1 into large unilamellar phosphatidylcholine vesicles was followed by monitoring tryptophan fluorescence. Peptide insertion was observed when the lipids were in the liquid-crystalline state [1-palmitoyl-2-oleoyl-siz-glycero-3-phosphocholine (POPC)] but not when they were in the crystalline phase [1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)]. Formation of a trimeric a-helical bundle in lipid bilayers was followed by fluorescence resonance energy transfer. Global fit analysis revealed a monomer-trimer equilibrium with a dissociation constant of around 10(-6) MF2. A lipid mixture composed of DPPC and POPC exhibiting a phase transition at 34 degrees C between a crystalline/liquid-crystalline coexistence region and a completely miscible liquid-crystalline phase was used to control the formation of the trimeric peptide bundle. TH1 is phase excluded in crystalline DPPC domains below 34 degrees C, leading to a larger number of trimers. However, when the DPPC domains are dispersed at temperatures above 34 degrees C, the number of trimers is reduced
Fluorinated interfaces drive self-association of transmembrane alpha helices in lipid bilayers
No full textAn increased tendency to self-assemble is exhibited by helical peptides with a highly fluorinated interface embedded in phospholipid membranes. A simultaneously hydrophobic and lipophobic surface obtained by replacing all interface leucine residues with hexafluoroleucine results in a significant increase in the ability of transmembrane helices to form higher-order ensembles. A=fluorescence acceptor; D=fluorescence donor
Charakterisierung und Kontrolle selbstorganisierter Peptidhelixbündel in Phospholipidmembranen
No full textIm Rahmen dieser Arbeit wurden die Wechselwirkungen der Peptide TMH-1 und TMH-2 und deren fluorinierter Analoga TMF-1 und TMF-2 mit Lipiddoppel-schichten untersucht. Die Peptide sind abgeleitet von der Aminosäuresequenz des GCN4-Zippers, von dem bekannt ist, dass er coiled coil-Strukturen ausbildet, wobei die hydrophoben durch hydrophile Reste ersetzt wurden, um die Lipidlöslichkeit zu gewährleisten.
Die Charakterisierung der Lipid-Peptid-Wechselwirkungen erfolgte in Phospholipidvesikeln bestehend aus 1-Palmitoyl-2-oleoyl-sn-glycero-3-phospho-cholin. Es konnte mit Hilfe des an Position vier befindlichen Tryptophan in der Sequenz aller Peptide über die Tryptophan-Fluoreszenz eine reversible Insertion der Moleküle in POPC-Doppelschichten nachgewiesen werden. Quenchingexperimente konnten im Falle der Peptide TMH-1 und TMH-2 eine Lokalisierung des Tryptophan-Rests in der Membran belegen. Dabei ergab sich der Abstand zwischen dem Tryptophan-Rest und dem Zentrum der Lipiddoppelschicht mit 1.5 nm für TMH-1 bzw. 1.9 nm für TMH-2. Mittels der Circulardichroismus-Spektroskopie wurde der -helikale Gehalt der Peptide in unterschiedlichen Medien bestimmt, der belegte, dass ein Helixanteil von 67 % im Falle des TMH-1 bzw. 42 % im Falle des TMH-2 insertiert in POPC-Vesikel erreicht wurde. Attenuated Total Reflection � Fourier Transformed Infrared � Experimente zeigten, dass die nicht fluorinierten Peptide in der Membran alle möglichen Orientierungen einnehmen.
Erstmals in Lipidvesikeln konnte die Ausbildung und die Stabilität von Peptidoligomeren der Peptide TMH-1 und TMH-2 gezeigt werden. Durch die Einführung fluorinierter Seitenketten in den Peptiden TMF-1 und TMF-2 konnte die Tendenz zur Aggregation erhöht werden. Dies wurde durch die ermittelten Dissoziationskonstanten von für TMH-1 und für TMF-1 belegt, die mittels Fluoreszenz Resonanz Energie Transfer bestimmt wurden. Zudem konnten für alle vier Peptide über FRET-Messungen die Zahl der Peptide in einem Oligomer in Lipidmembranen bestimmt werden.
Es konnte eine Methode basierend auf FRET entwickelt werden, um das Aggregationsverhalten der Peptide in Lipiddoppelschichten temperaturabhängig zu kontrollieren. Mit Hilfe von FRET-Experimenten an fluoreszenzgelabelten Lipiden wurde zunächst die Ausbildung von DPPC-haltigen Domänen in DPPC/POPC-Mischungen (6:4) unterhalb der Phasenumwandlungstemperatur bestätigt. Anschließend wurde das Peptid TMH-1 in die Lipiddoppelschicht insertiert und es konnte eindeutig belegt werden, dass durch Variation der Temperatur das Monomer-Trimer-Gleichgewicht der Peptidoligomerisierung in der Membran gesteuert werden konnte
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
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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