Página 20 dos resultados de 6914 itens digitais encontrados em 0.024 segundos

‣ A Structured Viroid RNA Serves as a Substrate for Dicer-Like Cleavage To Produce Biologically Active Small RNAs but Is Resistant to RNA-Induced Silencing Complex-Mediated Degradation▿

Itaya, Asuka; Zhong, Xuehua; Bundschuh, Ralf; Qi, Yijun; Wang, Ying; Takeda, Ryuta; Harris, Ann R.; Molina, Carlos; Nelson, Richard S.; Ding, Biao
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
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RNA silencing is a potent means of antiviral defense in plants and animals. A hallmark of this defense response is the production of 21- to 24-nucleotide viral small RNAs via mechanisms that remain to be fully understood. Many viruses encode suppressors of RNA silencing, and some viral RNAs function directly as silencing suppressors as counterdefense. The occurrence of viroid-specific small RNAs in infected plants suggests that viroids can trigger RNA silencing in a host, raising the question of how these noncoding and unencapsidated RNAs survive cellular RNA-silencing systems. We address this question by characterizing the production of small RNAs of Potato spindle tuber viroid (srPSTVds) and investigating how PSTVd responds to RNA silencing. Our molecular and biochemical studies provide evidence that srPSTVds were derived mostly from the secondary structure of viroid RNAs. Replication of PSTVd was resistant to RNA silencing, although the srPSTVds were biologically active in guiding RNA-induced silencing complex (RISC)-mediated cleavage, as shown with a sensor system. Further analyses showed that without possessing or triggering silencing suppressor activities, the PSTVd secondary structure played a critical role in resistance to RISC-mediated cleavage. These findings support the hypothesis that some infectious RNAs may have evolved specific secondary structures as an effective means to evade RNA silencing in addition to encoding silencing suppressor activities. Our results should have important implications in further studies on RNA-based mechanisms of host-pathogen interactions and the biological constraints that shape the evolution of infectious RNA structures.

‣ Cellular and biochemical events in mammalian cells during and after recovery from physiological stress

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/11/1986 Português
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We have examined and compared a number of cellular and biochemical events associated with the recovery process of rat fibroblasts placed under stress by different agents. Metabolic pulse-labeling studies of cells recovering from either heat-shock treatment, exposure to sodium arsenite, or exposure to an amino acid analogue of proline, L-azetidine 2-carboxylic acid, revealed interesting differences with respect to the individual stress proteins produced, their kinetics of induction, as well as the decay in their synthesis during the recovery period. In the initial periods of recovery, the major stress-induced 72-kD protein accumulates within the altered nucleoli in close association with the pre-ribosomal-containing granular region. During the later times of recovery from stress, the nucleoli begin to regain a normal morphology, show a corresponding loss of the 72-kD protein, and the majority of the protein now begins to accumulate within the cytoplasm in three distinct locales: the perinuclear region, along the perimeter of the cells, and finally in association with large phase-dense structures. These latter structures appear to consist of large aggregates of phase-dense material with no obvious encapsulating membrane. More interestingly we show...

‣ Immunolocalization of the cellular src protein in interphase and mitotic NIH c-src overexpresser cells

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/12/1990 Português
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The mouse mAb, mAb 327, that recognizes specifically both pp60v-src and pp60c-src in a wide variety of cells, has been used to determine precisely the various locations of pp60c-src in NIH c-src overexpresser cells, using the technique of immunofluorescence microscopy. In interphase cells, the protein exhibits two main distributions: one that appears uniform and in association with the cell surface and the other that is patchy and juxtanuclear and coincides with the centrosomes. The juxtanuclear aggregation of pp60c-src-containing patches depends on microtubules and does not seem to occur within the Golgi apparatus and the rough ER. At the G2-to-M-phase transition, a drastic change in the localization patterns of pp60c-src takes place. We also report experiments in which the NIH c-src overexpresser cells were exposed to Con A for various times to induce a redistribution of the cell surface Con A receptors. We show that, at each stage of the Con A-mediated endocytotic process, the Con A-receptor complexes redistribute into structures to which pp60c-src appears also to be associated: at first, into patches that form at the cell surface level and then, into a cap that stands at the cell center in a juxtanuclear position and that coincides with the Golgi apparatus. During this capping process...

‣ IMMUNE CYTOLYSIS: ELECTRON MICROSCOPIC LOCALIZATION OF CELLULAR ANTIGENS WITH FERRITIN-ANTIBODY CONJUGATES

Easton, John M.; Goldberg, Burton; Green, Howard
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/01/1962 Português
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Immune gamma globulin has been coupled to ferritin by the diisocyanate method of Singer. The final product ("ferroglobulin") had approximately 13 per cent of its gamma globulin coupled to ferritin, and roughly half of its ferritin coupled to gamma globulin. The uncoupled gamma globulin could be removed by ultracentrifugal sedimentation of the free ferritin and the ferritin-antibody conjugates. The characteristics of the native antibody were retained by the ferritin-antibody conjugates, for they could be precipitated by anti-gamma globulin antisera, and when used as antibodies, they reacted specifically with soluble and cellular antigens. Ferroglobulin preparations made from rabbit antisera against whole ascites tumor cells were incubated with the cells, and the location of ferritin determined by electron microscopy of thin-sectioned material. It was found that the immune ferroglobulins localized specifically on antigens of the cell membrane. Some of the ferritin label entered the cells by pinocytosis, but the ferritin-antibody units did not appear able to pass directly through the cell membrane into the cytoplasmic matrix. When cells were incubated with ferritin-labeled antibody and complement, antibody could be located in the cytoplasmic matrix...

‣ Mutagenesis of the Phosphatidylinositol 4,5-Bisphosphate (Pip2) Binding Site in the Nh2-Terminal Domain of Ezrin Correlates with Its Altered Cellular Distribution

Barret, Cécile; Roy, Christian; Montcourrier, Philippe; Mangeat, Paul; Niggli, Verena
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 27/11/2000 Português
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The cytoskeleton-membrane linker protein ezrin has been shown to associate with phosphatidyl-inositol 4,5-bisphosphate (PIP2)-containing liposomes via its NH2-terminal domain. Using internal deletions and COOH-terminal truncations, determinants of PIP2 binding were located to amino acids 12–115 and 233–310. Both regions contain a KK(X)nK/RK motif conserved in the ezrin/radixin/moesin family. K/N mutations of residues 253 and 254 or 262 and 263 did not affect cosedimentation of ezrin 1-333 with PIP2-containing liposomes, but their combination almost completely abolished the capacity for interaction. Similarly, double mutation of Lys 63, 64 to Asn only partially reduced lipid interaction, but combined with the double mutation K253N, K254N, the interaction of PIP2 with ezrin 1-333 was strongly inhibited. Similar data were obtained with full-length ezrin. When residues 253, 254, 262, and 263 were mutated in full-length ezrin, the in vitro interaction with the cytoplasmic tail of CD44 was not impaired but was no longer PIP2 dependent. This construct was also expressed in COS1 and A431 cells. Unlike wild-type ezrin, it was not any more localized to dorsal actin-rich structures, but redistributed to the cytoplasm without strongly affecting the actin-rich structures. We have thus identified determinants of the PIP2 binding site in ezrin whose mutagenesis correlates with an altered cellular localization.

‣ Sialidase NEU3 is a peripheral membrane protein localized on the cell surface and in endosomal structures

Zanchetti, Gabriele; Colombi, Paolo; Manzoni, Marta; Anastasia, Luigi; Caimi, Luigi; Borsani, Giuseppe; Venerando, Bruno; Tettamanti, Guido; Preti, Augusto; Monti, Eugenio; Bresciani, Roberto
Fonte: Portland Press Ltd. Publicador: Portland Press Ltd.
Tipo: Artigo de Revista Científica
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Sialidase NEU3 is also known as the plasma-membrane-associated form of mammalian sialidases, exhibiting a high substrate specificity towards gangliosides. In this respect, sialidase NEU3 modulates cell-surface biological events and plays a pivotal role in different cellular processes, including cell adhesion, recognition and differentiation. At the moment, no detailed studies concerning the subcellular localization of NEU3 are available, and the mechanism of its association with cellular membranes is still unknown. In the present study, we have demonstrated that sialidase NEU3, besides its localization at the plasma membrane, is present in intracellular structures at least partially represented by a subset of the endosomal compartment. Moreover, we have shown that NEU3 present at the plasma membrane is internalized and locates then to the recycling endosomal compartment. The enzyme is associated with the outer leaflet of the plasma membrane, as shown by selective cell-surface protein biotinylation. This evidence is in agreement with the ability of NEU3 to degrade gangliosides inserted into the plasma membrane of adjacent cells. Moreover, the mechanism of the protein association with the lipid bilayer was elucidated by carbonate extraction. Under these experimental conditions...

‣ A unique virus release mechanism in the Archaea

Bize, Ariane; Karlsson, Erik A.; Ekefjärd, Karin; Quax, Tessa E. F.; Pina, Mery; Prevost, Marie-Christine; Forterre, Patrick; Tenaillon, Olivier; Bernander, Rolf; Prangishvili, David
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Little is known about the infection cycles of viruses infecting cells from Archaea, the third domain of life. Here, we demonstrate that the virions of the archaeal Sulfolobus islandicus rod-shaped virus 2 (SIRV2) are released from the host cell through a mechanism, involving the formation of specific cellular structures. Large pyramidal virus-induced protrusions transect the cell envelope at several positions, rupturing the S-layer; they eventually open out, thus creating large apertures through which virions escape the cell. We also demonstrate that massive degradation of the host chromosomes occurs because of virus infection, and that virion assembly occurs in the cytoplasm. Furthermore, intracellular viral DNA is visualized by flow cytometry. The results show that SIRV2 is a lytic virus, and that the host cell dies as a consequence of elaborated mechanisms orchestrated by the virus. The generation of specific cellular structures for a distinct step of virus life cycle is known in eukaryal virus-host systems but is unprecedented in cells from other domains.

‣ A mathematical model to derive N-glycan structures and cellular enzyme activities from mass spectrometric data

Krambeck, Frederick J; Bennun, Sandra V; Narang, Someet; Choi, Sean; Yarema, Kevin J; Betenbaugh, Michael J
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
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Effective representation and characterization of biosynthetic pathways of glycosylation can be facilitated by mathematical modeling. This paper describes the expansion of a previously developed detailed model for N-linked glycosylation with the further application of the model to analyze MALDI-TOF mass spectra of human N-glycans in terms of underlying cellular enzyme activities. The glycosylation reaction network is automatically generated by the model, based on the reaction specificities of the glycosylation enzymes. The use of a molecular mass cutoff and a network pruning method typically limits the model size to about 10,000 glycan structures. This allows prediction of the complete glycan profile and its abundances for any set of assumed enzyme concentrations and reaction rate parameters. A synthetic mass spectrum from model-calculated glycan profiles is obtained and enzyme concentrations are adjusted to bring the theoretically calculated mass spectrum into agreement with experiment. The result of this process is a complete characterization of a measured glycan mass spectrum containing hundreds of masses in terms of the activities of 19 enzymes. In addition, a complete annotation of the mass spectrum in terms of glycan structure is produced...

‣ Three-Dimensional Culture Alters Primary Cardiac Cell Phenotype

Akins, Robert E.; Rockwood, Danielle; Robinson, Karyn G.; Sandusky, Daniel; Rabolt, John; Pizarro, Christian
Fonte: Mary Ann Liebert, Inc. Publicador: Mary Ann Liebert, Inc.
Tipo: Artigo de Revista Científica
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The directed formation of complex three-dimensional (3D) tissue architecture is a fundamental goal in tissue engineering and regenerative medicine. The growth of cells in 3D structures is expected to influence cellular phenotype and function, especially relative cell distribution, expression profiles, and responsiveness to exogenous signals; however, relatively few studies have been carried out to examine the effects of 3D reaggregation on cells from critical target organs, like the heart. Accordingly, we cultured primary cardiac ventricular cells in a 3D model system using a serum-free medium to test the hypothesis that expression profiles, multicellular organizational pathways, tissue maturation markers, and responsiveness to hormone stimulation were significantly altered in stable cell populations grown in 3D versus 2D culture. We found that distinct multi-cellular structures formed in 3D in conjunction with changes in mRNA expression profile, up-regulation of endothelial cell migratory pathways, decreases in the expression of fetal genes (Nppa and Ankrd1), and increased sensitivity to tri-iodothyronine stimulation when compared to parallel 2D cultures comprising the same cell populations. These results indicate that the culture of primary cardiac cells in 3D aggregates leads to physiologically relevant alterations in component cell phenotype consistent with cardiac ventricular tissue formation and maturation.

‣ Large facilities and the evolving ribosome, the cellular machine for genetic-code translation

Yonath, Ada
Fonte: The Royal Society Publicador: The Royal Society
Tipo: Artigo de Revista Científica
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Well-focused X-ray beams, generated by advanced synchrotron radiation facilities, yielded high-resolution diffraction data from crystals of ribosomes, the cellular nano-machines that translate the genetic code into proteins. These structures revealed the decoding mechanism, localized the mRNA path and the positions of the tRNA molecules in the ribosome and illuminated the interactions of the ribosome with initiation, release and recycling factors. They also showed that the ribosome is a ribozyme whose active site is situated within a universal symmetrical region that is embedded in the otherwise asymmetric ribosome structure. As this highly conserved region provides the machinery required for peptide bond formation and for ribosome polymerase activity, it may be the remnant of the proto-ribosome, a dimeric pre-biotic machine that formed peptide bonds and non-coded polypeptide chains. Synchrotron radiation also enabled the determination of structures of complexes of ribosomes with antibiotics targeting them, which revealed the principles allowing for their clinical use, revealed resistance mechanisms and showed the bases for discriminating pathogens from hosts, hence providing valuable structural information for antibiotics improvement.

‣ Adaptive optics and the eye (super resolution OCT)

Miller, D T; Kocaoglu, O P; Wang, Q; Lee, S
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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The combination of adaptive optics (AO) and optical coherence tomography (OCT) was first reported 8 years ago and has undergone tremendous technological advances since then. The technical benefits of adding AO to OCT (increased lateral resolution, smaller speckle, and enhanced sensitivity) increase the imaging capability of OCT in ways that make it well suited for three-dimensional (3D) cellular imaging in the retina. Today, AO–OCT systems provide ultrahigh 3D resolution (3 × 3 × 3 μm3) and ultrahigh speed (up to an order of magnitude faster than commercial OCT). AO–OCT systems have been used to capture volume images of retinal structures, previously only visible with histology, and are being used for studying clinical conditions. Here, we present representative examples of cellular structures that can be visualized with AO–OCT. We overview three studies from our laboratory that used ultrahigh-resolution AO–OCT to measure the cross-sectional profiles of individual bundles in the retinal nerve fiber layer; the diameters of foveal capillaries that define the terminal rim of the foveal avascular zone; and the spacing and length of individual cone photoreceptor outer segments as close as 0.5° from the fovea center.

‣ Intercellular Communication by Exchange of Cytoplasmic Material via Tunneling Nano-Tube Like Structures in Primary Human Renal Epithelial Cells

Domhan, Sophie; Ma, Lili; Tai, Albert; Anaya, Zachary; Beheshti, Afshin; Zeier, Martin; Hlatky, Lynn; Abdollahi, Amir
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 27/06/2011 Português
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Transfer of cellular material via tunneling nanotubes (TNT) was recently discovered as a novel mechanism for intercellular communication. The role of intercellular exchange in communication of renal epithelium is not known. Here we report extensive spontaneous intercellular exchange of cargo vesicles and organelles between primary human proximal tubular epithelial cells (RPTEC). Cells were labeled with two different quantum dot nanocrystals (Qtracker 605 or 525) and intercellular exchange was quantified by high-throughput fluorescence imaging and FACS analysis. In co-culture, a substantial fraction of cells (67.5%) contained both dyes indicating high levels of spontaneous intercellular exchange in RPTEC. The double positive cells could be divided into three categories based on the preponderance of 605 Qtracker (46.30%), 525 Qtracker (48.3%) and approximately equal content of both Qtrackers (4.57%). The transfer of mitochondria between RPTECs was also detected using an organelle specific dye. Inhibition of TNT genesis by actin polymerization inhibitor (Latrunculin B) markedly reduced intercellular exchange (>60%) suggesting that intercellular exchange in RPTEC was in part mediated via TNT-like structures. In contrast, induction of cellular stress by Zeocin treatment increased tube-genesis in RPTEC. Our data indicates an unexpected dynamic of intercellular communication between RPTEC by exchange of cytosolic material...

‣ Three-Dimensional Polymer Constructs Exhibiting a Tunable Negative Poisson’s Ratio

Fozdar, David Y.; Soman, Pranav; Lee, Jin Woo; Han, Li-Hsin; Chen, Shaochen
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 22/07/2011 Português
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Young’s modulus and Poisson’s ratio of a porous polymeric construct (scaffold) quantitatively describe how it supports and transmits external stresses to its surroundings. While Young’s modulus is always non-negative and highly tunable in magnitude, Poisson’s ratio can, indeed, take on negative values despite the fact that it is non-negative for virtually every naturally occurring and artificial material. In some applications, a construct having a tunable negative Poisson’s ratio (an auxetic construct) may be more suitable for supporting the external forces imposed upon it by its environment. Here, three-dimensional polyethylene glycol scaffolds with tunable negative Poisson’s ratios are fabricated. Digital micromirror device projection printing (DMD-PP) is used to print single-layer constructs composed of cellular structures (pores) with special geometries, arrangements, and deformation mechanisms. The presence of the unit-cellular structures tunes the magnitude and polarity (positive or negative) of Poisson’s ratio. Multilayer constructs are fabricated with DMD-PP by stacking the single-layer constructs with alternating layers of vertical connecting posts. The Poisson’s ratios of the single- and multilayer constructs are determined from strain experiments...

‣ The Homolog of the Five SH3-Domain Protein (HOFI/SH3PXD2B) Regulates Lamellipodia Formation and Cell Spreading

Lányi, Árpád; Baráth, Mónika; Péterfi, Zalán; Bőgel, Gábor; Orient, Anna; Simon, Tünde; Petrovszki, Enikő; Kis-Tóth, Katalin; Sirokmány, Gábor; Rajnavölgyi, Éva; Terhorst, Cox; Buday, László; Geiszt, Miklós
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 23/08/2011 Português
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Motility of normal and transformed cells within and across tissues requires specialized subcellular structures, e.g. membrane ruffles, lamellipodia and podosomes, which are generated by dynamic rearrangements of the actin cytoskeleton. Because the formation of these sub-cellular structures is complex and relatively poorly understood, we evaluated the role of the adapter protein SH3PXD2B [HOFI, fad49, Tks4], which plays a role in the development of the eye, skeleton and adipose tissue. Surprisingly, we find that SH3PXD2B is requisite for the development of EGF-induced membrane ruffles and lamellipodia, as well as for efficient cellular attachment and spreading of HeLa cells. Furthermore, SH3PXD2B is present in a complex with the non-receptor protein tyrosine kinase Src, phosphorylated by Src, which is consistent with SH3PXD2B accumulating in Src-induced podosomes. Furthermore, SH3PXD2B closely follows the subcellular relocalization of cortactin to Src-induced podosomes, EGF-induced membrane ruffles and lamellipodia. Because SH3PXD2B also forms a complex with the C-terminal region of cortactin, we propose that SH3PXD2B is a scaffold protein that plays a key role in regulating the actin cytoskeleton via Src and cortactin.

‣ The Cellular Chaperone Hsc70 Is Specifically Recruited to Reovirus Viral Factories Independently of Its Chaperone Function

Kaufer, Susanne; Coffey, Caroline M.; Parker, John S. L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2012 Português
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Mammalian orthoreoviruses replicate and assemble in the cytosol of infected cells. A viral nonstructural protein, μNS, forms large inclusion-like structures called viral factories (VFs) in which assembling viral particles can be identified. Here we examined the localization of the cellular chaperone Hsc70 and found that it colocalizes with VFs in infected cells and also with viral factory-like structures (VFLs) formed by ectopically expressed μNS. Small interfering RNA (siRNA)-mediated knockdown of Hsc70 did not affect the formation or maintenance of VFLs. We further showed that dominant negative mutants of Hsc70 were also recruited to VFLs, indicating that Hsc70 recruitment to VFLs is independent of the chaperone function. In support of this finding, μNS was immunoprecipitated with wild-type Hsc70, with a dominant negative mutant of Hsc70, and with the minimal substrate-binding site of Hsc70 (amino acids 395 to 540). We identified a minimal region of μNS between amino acids 222 and 271 that was sufficient for the interaction with Hsc70. This region of μNS has not been assigned any function previously. However, neither point mutants with alterations in this region nor the complete deletion of this domain abrogated the μNS-Hsc70 interaction...

‣ How myosin motors power cellular functions : an exciting journey from structure to function

Llinas, Paola; Pylypenko, Olena; Isabet, Tatiana; Mukherjea, Monalisa; Sweeney, H. Lee; Houdusse, Anne M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Molecular motors such as myosins are allosteric enzymes that power essential motility functions in the cell and structural biology is an important tool to decipher how these motors work. Force is produced by myosins upon the actin-driven conformational changes that control the sequential release of the hydrolysis products of ATP (Pi followed by ADP). These conformational changes are amplified by a “lever arm” that includes the region of the motor known as the converter and the adjacent elongated light chain binding region. Analysis of four structural states of the motor provides a detailed understanding of the rearrangements and pathways of communication in the motor necessary for detachment from the actin track and repriming of the motor. However, the important part of the cycle in which force is produced remains enigmatic and awaits new high resolution structures. The value of a structural approach is particularly evident from the clues that have been provided from the structural states of the reverse myosin VI motor. Crystallographic structures have revealed that rearrangements within the converter subdomain occur which explains why this myosin can produce a large stroke in the opposite direction of all other myosins despite a very short lever arm. By providing detailed understanding of the motor rearrangements...

‣ The Effects of Intracellular Organelles on the ADC of Water Molecules in Cultured Human Embryonic Kidney Cells

Colvin, Daniel C.; Jourquin, Jerome; Xu, Junzhong; Does, Mark D.; Estrada, Lourdes; Gore, John C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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The apparent diffusion coefficient (ADC) of water in tissues is dependent upon the size and spacing of structures in the cellular environment, and has been used to characterize pathological changes in stroke and cancer. However, the factors that affect ADC values remain incompletely understood. Measurements of ADC are usually made using relatively long diffusion times, so they reflect the integrated effects of cellular structures over a broad range of spatial scales. We used temporal diffusion spectroscopy to study diffusion in packed cultured human embryonic kidney cells over a range of effective diffusion times following microtubule and actin/cytoskeleton depolymerization, and disassembly of the Golgi complex. While Golgi disruption did not change ADC, depolymerization of the microtubule and the actin filament networks caused small decreases in ADC at short diffusion times only. Temporal diffusion spectroscopy provided a novel way to assess intracellular influences on the diffusion properties of tissue water.

‣ Ligand binding PAS domains in a genomic, cellular, and structural context

Henry, Jonathan T.; Crosson, Sean
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
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Per-Arnt-Sim (PAS) domains occur in proteins from all kingdoms of life. In the bacterial kingdom, PAS domains are commonly positioned at the amino terminus of signaling proteins such as sensor histidine kinases, cyclic-di-GMP synthases/hydrolases, and methyl-accepting chemotaxis proteins. Although these domains are highly divergent at the primary sequence level, the structures of dozens of PAS domains across a broad section of sequence space have been solved, revealing a conserved three-dimensional architecture. An all-versus-all alignment of 63 PAS structures demonstrates that the PAS domain family forms structural clades on the basis of two principal variables: (a) topological location inside or outside the plasma membrane and (b) the class of small molecule that they bind. The binding of a chemically diverse range of small-molecule metabolites is a hallmark of the PAS domain family. PAS ligand binding either functions as a primary cue to initiate a cellular signaling response or provides the domain with the capacity to respond to secondary physical or chemical signals such as gas molecules, redox potential, or photons. This review synthesizes the current state of knowledge of the structural foundations and evolution of ligand recognition and binding by PAS domains.

‣ Cellular function and molecular structure of ecto-nucleotidases

Zimmermann, Herbert; Zebisch, Matthias; Sträter, Norbert
Fonte: Springer Netherlands Publicador: Springer Netherlands
Tipo: Artigo de Revista Científica
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Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5′-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution...

‣ DECONSTRUCTING THE PERINEURONAL NET: CELLULAR CONTRIBUTIONS AND MOLECULAR COMPOSITION OF THE NEURONAL EXTRACELLULAR MATRIX

GIAMANCO, K. A.; MATTHEWS, R. T.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Perineuronal nets (PNNs) are lattice-like substructures of the neural extracellular matrix that enwrap particular populations of neurons throughout the central nervous system. Previous work suggests that this structure plays a major role in modulating developmental neural plasticity and brain maturation. Understanding the precise role of these structures has been hampered by incomplete comprehension of their molecular composition and cellular contributions to their formation, which is studied herein using primary cortical cell cultures. By defining culture conditions to reduce (cytosine-β-D-arabinofuranoside/AraC addition) or virtually eliminate (elevated KCl and AraC application) glia, PNN components impacted by this cell type were identified. Effects of depolarizing KCl concentrations alone were also assessed. Our work identified aggrecan as the primary neuronal component of the PNN and its expression was dramatically up-regulated by both depolarization and glial cell inhibition and additionally, the development of aggrecan-positive PNNs was accelerated. Surprisingly, most of the other PNN components tested were made in a glial-dependent manner in our culture system. Interestingly, in the absence of these glial-derived components...