1,721,033 research outputs found
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
Investigating the functional and structural modulation of carboxysomes in Synechococcus elongatus PCC7942
Full text linkVariations 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
Repurposing Bacterial CO2-fixing Organelles Using Synthetic Engineering
Full text linkBacterial microcompartments (BMCs) are protein-based organelles widespread among bacterial phyla and provide a means for compartmentalization of specific metabolic pathways. They sequester catalytic enzymes from the cytoplasm, using an icosahedral proteinaceous shell with selective permeability to metabolic molecules and substrates, to enhance metabolic efficiency. Carboxysomes were the first BMCs discovered, and their unprecedented capacity of CO2 fixation allows cyanobacteria to make a significant contribution to global carbon fixation. The carboxysome was classified as α- and β-carboxysome according to the Rubisco form. The shell of the carboxysome ensures preferable transport of bicarbonate and CO2 assimilation, making the carboxysome as an ideal nanobioreactor. Assembly studies and functional characterization of synthetic carboxysomes are important for understanding the assembly of carboxysomes in native and heterologous hosts. Moreover, there is an increasing interest in utilizing synthetic biology to construct synthetic carboxysomes or carboxysome shells in new hosts, i.e., higher plants, to enhance carbon fixation and productivity.
In Chapter 1, I summarized the research background and aims of the PhD project. In Chapter 3, I described the construction of a synthetic operon of β-carboxysomes from the cyanobacterium Synechococcus elongatus PCC7942 and the synthetic production of functional β-carboxysome structures in Escherichia coli. The structure, assembly, activity and interchangeability of synthetic β-carboxysomes were assessed using confocal, electron and atomic force microscopy, proteomics, immunoblot analysis, and enzymatic assays. To our knowledge, this is the first production of functional β-carboxysomes in heterologous organisms. In Chapter 4, the α-carboxysomes from the chemoautotroph Halothiobacillus neapolitanus were heterogeneous synthesized in E. coli. To improve the activity, the Rubisco activase CbbQO complex was introduced to the α-carboxysome expression system. We found that the addition of Rubisco activase CbbQ can improve the function of the synthetic carboxysomes and didn’t affect the assembly of synthetic carboxysomes. In Chapter 5, the synthetic α-carboxysome shell was constructed and characterized. In Chapter 6, I summarized the results and prospect the future perspectives for my projects.
This study strengthens synthetic biology toolbox for generating not only functional carboxysome structures but also BMC-like organelles with tunable activities and BMC shell. It will inform the improvement of carboxysome engineering and the construction of functional CO2-fixing modules for plant engineering as well as new nanoreactors
Determining the Macromolecular Structures of Photosynthetic Supercomplexes from Rhodobacter using Cryo-Electron Microscopy
Full text linkThe reaction center (RC)−light-harvesting complex 1 (LH1) supercomplex plays a central role in bacterial photosynthesis by converting light into chemical energy. Some RC–LH1 complexes integrate an additional protein PufX which is key for bacterial growth and photosynthetic competence. This thesis presents the atomic models of RC−LH1−PufX complexes from three species of purple bacteria: Rhodobacter (Rba.) sphaeroides, Rba. veldkampii and Rba. capsulatus. Electron potential maps used to build the models were obtained by single particle cryo-electron microscopy at resolutions of 2.84 Å (Rba. veldkampii), 3.40 Å and 2.79 Å (Rba. sphaeroides), and 2.59 Å (Rba. capsulatus). The RC–LH1–PufX native monomers of Rba. veldkampii and Rba. capsulatus contain LH1 rings comprised of 15 αβ-heterodimers featuring a gap formed by PufX. The RC−LH1−PufX native dimer of Rba. sphaeroides contains an S-shaped LH1 ring of 28 αβ-heterodimers with two large gaps formed by PufX polypeptides, and an additional polypeptide PufY inserted between the LH1 ring and the RC near each gap. In order to understand the process of dimerization and the structural impacts of the additional polypeptides PufX and PufY, we also characterized the native monomer and three mutant complexes: one without the PufX, one without the PufY and one with PufX replaced with PufX of a strictly monomeric complex from Rba. veldkampii.
The presented high-resolution WT and mutant structures provided insights into monomeric and dimeric RC‒LH1 complex formation, quinone pathway and roles of polypeptides PufX and PufY. PufX was observed to mediate dimerization through its N-terminus, correct complex assembly and halting the LH1 ring elongation resulting in a characteristic open architecture. PufY was observed to possibly stabilize the LH1 ring, increasing the efficiency of excitation energy transfer and potentially helping with quinone navigation. The features, similarities and differences displayed by RC‒LH1‒PufX complexes serve as a structural basis for understanding the mechanism of anoxygenic photosynthesis, as well as environmental adaptation and evolution of photosynthetic systems
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
Distribution and dynamics of electron transport complexes in cyanobacterial thylakoid membranes
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Organization, dynamics and adaptation of the photosynthetic machinery in cyanobacteria
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