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Get PDFWe recently reported that the C2AB portion of Synaptotagmin 1 (Syt1) could selfassemble into Ca2+-sensitive ring-like oligomers on membranes, which could potentially regulate neurotransmitter release. Here we report that analogous ring-like oligomers assemble from the C2AB domains of other Syt isoforms (Syt2, Syt7, Syt9) as well as related C2 domain containing protein, Doc2B and extended Synaptotagmins (E-Syts). Evidently, circular oligomerization is a general and conserved structural aspect of many C2 domain proteins, including Synaptotagmins. Further, using electron microscopy combined with targeted mutations, we show that under physiologically relevant conditions, both the Syt1 ring assembly and its rapid disruption by Ca2+ involve the well-established functional surfaces on the C2B domain that are important for synaptic transmission. Our data suggests that ring formation may be triggered at an early step in synaptic vesicle docking and positions Syt1 to synchronize neurotransmitter release to Ca2+ influx.Fil: Zanetti, Maria Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Bello, Oscar Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; ArgentinaFil: Wang, Jing. University of Yale. School of Medicine; Estados UnidosFil: Coleman, Jeff. University of Yale. School of Medicine; Estados UnidosFil: Cai, Yiying. University of Yale. School of Medicine; Estados UnidosFil: Sindelar, Charles V.. University of Yale. School of Medicine; Estados UnidosFil: Rothman, James E.. University of Yale. School of Medicine; Estados UnidosFil: Krishnakumar, Shyam S.. University of Yale. School of Medicine; Estados Unido
Synaptotagmin oligomerization is essential for calcium control of regulated exocytosis
Get PDFRegulated exocytosis, which underlies many intercellular signaling events, is a tightly controlled process often triggered by calcium ion(s) (Ca2+). Despite considerable insight into the central components involved, namely, the core fusion machinery [soluble N-ethylmaleimide?sensitive factor attachment protein receptor (SNARE)] and the principal Ca2+ sensor [C2-domain proteins like synaptotagmin (Syt)], the molecular mechanism of Ca2+-dependent release has been unclear. Here, we report that the Ca2+-sensitive oligomers of Syt1, a conserved structural feature among several C2-domain proteins, play a critical role in orchestrating Ca2+-coupled vesicular release. This follows from pHluorin-based imaging of single-vesicle exocytosis in pheochromocytoma (PC12) cells showing that selective disruption of Syt1 oligomerization using a structure-directed mutation (F349A) dramatically increases the normally low levels of constitutive exocytosis to effectively occlude Ca2+-stimulated release. We propose a parsimonious model whereby Ca2+-sensitive oligomers of Syt (or a similar C2-domain protein) assembled at the site of docking physically block spontaneous fusion until disrupted by Ca2+. Our data further suggest Ca2+-coupled vesicular release is triggered by removal of the inhibition, rather than by direct activation of the fusion machinery.Fil: Bello, Oscar Daniel. University of Yale. School of Medicine; Estados Unidos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto de Histologia y Embriologia de Mendoza Dr. Mario H. Burgos. Grupo Vinculado de Investigacion y Desarrollo Biotecnologico Aplicado Al Diagnostico Al Ihem | Universidad Nacional de Cuyo. Facultad de Ciencias Medicas. Instituto de Histologia y Embriologia de Mendoza Dr. Mario H. Burgos. Grupo Vinculado de Investigacion y Desarrollo Biotecnologico Aplicado Al Diagnostico Al Ihem.; Argentina. University College London; Estados UnidosFil: Jouannot, Ouardane. University of Yale. School of Medicine; Estados UnidosFil: Chaudhuri, Arunima. University of Yale. School of Medicine; Estados UnidosFil: Stroeva, Ekaterina. University of Yale. School of Medicine; Estados UnidosFil: Coleman, Jeff. University of Yale. School of Medicine; Estados UnidosFil: Volynski, Kirill E.. University College London; Reino UnidoFil: Rothman, James E.. University of Yale. School of Medicine; Estados Unidos. University College London; Estados UnidosFil: Krishnakumar, Shyam S.. University of Yale. School of Medicine; Estados Unidos. University College London; Estados Unido
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Sequence to Topography Relationship in Membrane-Inserted Hydrophobic Helics
Get PDFHydrophobic α-helices have been widely used to study membrane protein sequencestructure relationships in model membranes. Our lab has developed fluorescence methods to determine the topography of membrane-inserted hydrophobic helices, and to understand the equilibria describing their topographic stability. Using this model membrane system, the minimum hydrophobic length necessary to form a transmembrane (TM) helix in membranes was investigated. Sequences with 13 consecutive hydrophobic residues were found to be the minimum necessary to form a predominantly TM state in a bilayer with a biologically relevant width. The ability of these short hydrophobic sequences to form TM helices in the presence of substantial negative mismatch (~10 Å) implied that lipid bilayers have a considerable ability to adjust to hydrophobic mismatch. In addition, the ability of hydrophilic residues to shift the transverse position of the TM helices within the bilayer was studied. Hydrophilic residues at some positions within iv hydrophobic helices induced transverse shifts in TM helix position such that the polar residue moved closer to the bilayer surface. The extent of shift depended on the identity of the hydrophilic residue. The shift was controlled by the combination of amino acid hydrophilicity, ionization state and the ability of the side chains to position the polar groups near the bilayer surface (snorkeling). Furthermore, the structural consequence of pathogenic hydrophilic mutations in the TM domain of neu/ErbB2 receptor was investigated. Hydrophilic mutations in the TM domain were found to alter the membrane position of the TM helix and thus redefine the transmembrane boundary. This suggested a new mode of receptor upregulation in the neu/ErbB2 oncogene. Finally, in collaboration with Dr. Eckard Wimmer, Department of Molecular Genetic and Microbiology, the membrane topography of poliovirus proteins 3A and 3AB was characterized. Fluorescence studies showed that the hydrophobic domain forms a stable TM structure in mature 3A protein, but adopts a non-TM surface topography in context of the precursor 3AB protein. The hydrophobic sequence could insert in a TM form, only when the Ctermini 3B domain was removed. Furthermore, a shortened C-terminal part of the putative hydrophobic segment (16 residues rather than 22 residues) was found to span the lipid bilayer
Sequence to Topography Relationship in Membrane-Inserted Hydrophobic Helics
No full textStony Brook University Libraries.
SBU Graduate School in Biochemistry and Structural Biology.
Lawrence Martin (Dean of Graduate School), Dr. Erwin London, Ph.D. Professor
Department of Biochemistry and Cell Biology
Dissertation Advisor, Dr. Robert Haltiwanger, Ph.D. Professor
Department of Biochemistry and Cell Biology
Chairperson of Dissertation Committee, Dr. Steven O. Smith, Ph.D. Professor,
Department of Biochemistry and Cell Biology, Dr. James B. Konopka, Ph.D. Professor,
Department of Molecular Genetics and Microbiology
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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