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  • 1
    Publication Date: 2015-07-23
    Description: Bacteria share their ecological niches with other microbes. The bacterial type VI secretion system is one of the key players in microbial competition, as well as being an important virulence determinant during bacterial infections. It assembles a nano-crossbow-like structure in the cytoplasm of the attacker cell that propels an arrow made of a haemolysin co-regulated protein (Hcp) tube and a valine-glycine repeat protein G (VgrG) spike and punctures the prey's cell wall. The nano-crossbow is stably anchored to the cell envelope of the attacker by a membrane core complex. Here we show that this complex is assembled by the sequential addition of three type VI subunits (Tss)-TssJ, TssM and TssL-and present a structure of the fully assembled complex at 11.6 A resolution, determined by negative-stain electron microscopy. With overall C5 symmetry, this 1.7-megadalton complex comprises a large base in the cytoplasm. It extends in the periplasm via ten arches to form a double-ring structure containing the carboxy-terminal domain of TssM (TssMct) and TssJ that is anchored in the outer membrane. The crystal structure of the TssMct-TssJ complex coupled to whole-cell accessibility studies suggest that large conformational changes induce transient pore formation in the outer membrane, allowing passage of the attacking Hcp tube/VgrG spike.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Durand, Eric -- Nguyen, Van Son -- Zoued, Abdelrahim -- Logger, Laureen -- Pehau-Arnaudet, Gerard -- Aschtgen, Marie-Stephanie -- Spinelli, Silvia -- Desmyter, Aline -- Bardiaux, Benjamin -- Dujeancourt, Annick -- Roussel, Alain -- Cambillau, Christian -- Cascales, Eric -- Fronzes, Remi -- England -- Nature. 2015 Jul 30;523(7562):555-60. doi: 10.1038/nature14667. Epub 2015 Jul 22.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Laboratoire d'Ingenierie des Systemes Macromoleculaires, Aix-Marseille Universite - CNRS, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France [2] Architecture et Fonction des Macromolecules Biologiques, CNRS, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France [3] G5 Biologie structurale de la secretion bacterienne, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [4] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [5] AFMB, Aix-Marseille Universite, IHU Mediterranee Infection, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France. ; 1] Architecture et Fonction des Macromolecules Biologiques, CNRS, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France [2] AFMB, Aix-Marseille Universite, IHU Mediterranee Infection, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France. ; Laboratoire d'Ingenierie des Systemes Macromoleculaires, Aix-Marseille Universite - CNRS, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. ; UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France. ; 1] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [2] Unite de Bioinformatique Structurale, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France. ; 1] G5 Biologie structurale de la secretion bacterienne, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France [2] UMR 3528, CNRS, Institut Pasteur, 25-28 rue du Docteur Roux, 75015 Paris, France.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26200339" target="_blank"〉PubMed〈/a〉
    Keywords: *Bacterial Secretion Systems ; Cell Membrane/chemistry/metabolism ; Crystallography, X-Ray ; Cytoplasm/chemistry/metabolism ; Escherichia coli/*chemistry/metabolism ; Escherichia coli Proteins/biosynthesis/*chemistry ; Lipopeptides/biosynthesis/*chemistry ; Membrane Proteins/biosynthesis/*chemistry ; Microscopy, Electron ; Models, Molecular ; Multiprotein Complexes/*biosynthesis/*chemistry ; Periplasm/chemistry/metabolism ; Porosity ; Protein Structure, Tertiary ; Protein Subunits/biosynthesis/chemistry
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    ISSN: 1432-1106
    Keywords: Retinal ganglion cells ; Dendritic field ; Retinal distribution ; Horseradish peroxidase ; Cobaltic-lysine complex ; Bufo marinus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The retrograde transport of horseradish peroxidase (HRP) and cobaltic-lysine complex (CLC) was used to morphologically characterize large ganglion cells (GCs) and to determine their distribution in retinal wholemounts and in sectioned material in the retina ofBufo marinus. Large GCs, amounting to about 0.5% of total GC population, were defined to be those with very large dendritic field sizes varying between 0.1 mm2 to 0.6 mm2 and cell soma sizes of between 100 μm2 to 400 μm2. These cells were subdivided into 3 major groups, Types I, II and III, on the basis of their dendritic field sizes, arborization patterns and the strata of dendritic branching within the inner plexiform layer (IPL). The majority of large neurons (about 90%) were classified as Type I GCs with symmetrical dendritic arbor. These cells had either bistratified branching in the scierai and vitreal sublaminae of the IPL (65% of Type I Cells) or unistratified branching in the scleral (26%) or in the vitreal (9%) sublamina. Their dendritic field sizes increased linearly from the retinal centre from 0.13 mm±0.02 mm2 (mean and S.D.) to 0.58±0.11 mm2 in the retinal periphery. Type II GCs (about 9% of the large GC population) were characterized by an asymmetrical dendritic arborization directed towards the ciliary margin with unistratified branching in the scierai sublamina of the IPL. The mean dendritic field sizes of these cells were 0.26±0.09 mm2. Type III GCs, the least frequent (about 1%) category of large GCs had sparsely branching, elongated dendritic branching aligned approximately parallel with the nasotemporal axis of the retina. The unistratified dendritic branches of these neurons were located in the vitreal sublamina of the IPL with a mean dendritic field size of 0.42±0.11 mm2. The dendritic field sizes of Types II and III GCs did not increase with retinal eccentricity. Type I GCs were distributed unevenly across the retina, the density being greatest in the visual streak, along the nasotemporal meridian of the retina. The dendritic field sizes of these cells increased towards the retinal periphery, resulting in a constant dendritic field coverage factor across the retina. Each retinal point was covered by the dendritic fields of 4–5 adjacent GCs. In contrast, Types II and III GCs had only discontinuous dendritic coverage. The identification of morphological types of large GCs with previously described functional classes of GCs in the anuran retina is discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1106
    Keywords: Retinal ganglion cells ; Displaced amacrine cells ; Development ; Visual streak ; Bufo marinus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The number and distribution of neurons in the retinal ganglion cell layer were studied from the metamorphic climax to adulthood in the toad Bufo marinus. Retinal wholemounts stained with cresyl violet showed that total neuron numbers increased from 55,000 at metamorphic climax to about 950,000 in adult animals. During the same time the entire retinal area increased 46-fold from an average 3.4 mm2 to 157 mm2. The morphological character of the neurons and their density across the retina changed during development. In metamorphosing animals, the neurons of the ganglion cell layer had a uniform appearance and their density increased slightly from the centre to the dorsal ciliary margin. After metamorphosis a high neuron density area, the visual streak, evolved in the retinal centre, resulting in the formation of a 6 to 1 density gradient from the visual streak out to the dorsal and ventral retinal poles in adult animals. Optic fibre numbers in juvenile and adult optic nerves were estimated to be 330,000 and 745,000, respectively, corresponding to similar ganglion cell numbers. One optic nerve was sectioned in a few animals and 4 weeks later the number of intact neurons — assumed to be displaced amacrine cells (DA) — was estimated. They amounted to 80,000 in juvenile and 189,000 in adult animals or about 20% of the total neuron population of the retinal ganglion cell layer, the remaining 80% being GC. A 1.7 to 1 density gradient of DA from the visual streak out to the dorsal and ventral retinal periphery was established. These results show that the visual streak evolves after metamorphosis from an originally uniform neuron distribution of the retinal ganglion cell layer. The possible mechanisms of the formation of the visual streak are discussed.
    Type of Medium: Electronic Resource
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