11,053 research outputs found
Investigation of nonlinear interaction phenomena in the ionosphere
Ionospheric phenomena as thermal radiation noise, propagation of naturally occurring radio noise through ionosphere, and generation of very low frequency emission
Identification of the Plasticity-Relevant Fucose-α(1−2)-Galactose Proteome from the Mouse Olfactory Bulb
Fucose-α(1−2)-galactose [Fucα(1−2)Gal] sugars have been implicated in the molecular mechanisms that underlie neuronal development, learning, and memory. However, an understanding of their precise roles has been hampered by a lack of information regarding Fucα(1−2)Gal glycoproteins. Here, we report the first proteomic studies of this plasticity-relevant epitope. We identify five classes of putative Fucα(1−2)Gal glycoproteins: cell adhesion molecules, ion channels and solute carriers/transporters, ATP-binding proteins, synaptic vesicle-associated proteins, and mitochondrial proteins. In addition, we show that Fucα(1−2)Gal glycoproteins are enriched in the developing mouse olfactory bulb (OB) and exhibit a distinct spatiotemporal expression that is consistent with the presence of a “glycocode” to help direct olfactory sensory neuron (OSN) axonal pathfinding. We find that expression of Fucα(1−2)Gal sugars in the OB is regulated by the α(1−2)fucosyltransferase FUT1. FUT1-deficient mice exhibit developmental defects, including fewer and smaller glomeruli and a thinner olfactory nerve layer, suggesting that fucosylation contributes to OB development. Our findings significantly expand the number of Fucα(1−2)Gal glycoproteins and provide new insights into the molecular mechanisms by which fucosyl sugars contribute to neuronal processes
Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 1097
NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the
elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1
nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes
connected to the ring extend almost continuously out to the bar. The other ends
of the dust lanes attach to two main spiral arms. To provide a physical
understanding of its structural and kinematical properties, two-dimensional
hydrodynamical simulations have been carried out. Numerical calculations reveal
that many features of the gas morphology and kinematics can be reproduced
provided that the gas flow is governed by a gravitational potential associated
with a slowly rotating strong bar. By including the self-gravity of the gas
disk in our calculation, we have found the starburst ring to be gravitationally
unstable which is consistent with the observation in \citet{hsieh11}. Our
simulations show that the gas inflow rate is 0.17 M_\sun yr into the
region within the starburst ring even after its formation, leading to the
coexistence of both a nuclear ring and a circumnuclear disk.Comment: 32 pages, 14 figures, 1 table, accepted for publication in the Ap
The Chemical Neurobiology of Carbohydrates
The cell surface displays a complex array of oligosaccharides, glycoproteins, and glycolipids. This diverse mixture of glycans contains a wealth of information, modulating a wide range of processes such as cell migration, proliferation, transcriptional regulation, and differentiation. Glycosylation is one of the most ubiquitous forms of post-translational modification, with more than 50% of the human proteome estimated to be glycosylated. Glycosylation adds another dimension to the complexity of cellular signaling and expands the ability of a cell to modulate protein function. The structural complexity of glycan modifications ranges from the addition of a single monosaccharide unit to polysaccharides containing hundreds of sugars in branched or linear arrays. This chemical diversity enables glycans to impart a vast array of functions, from structural stability and proteolytic protection to protein recognition and modulation of cell signaling networks.
Emerging evidence suggests a pivotal role for glycans in regulating nervous system development and function. For instance, glycosylation influences various neuronal processes, such as neurite outgrowth and morphology, and may contribute to the molecular events that underlie learning and memory. Glycosylation is an efficient modulator of cell signaling and has been implicated in memory consolidation pathways. Genetic ablation of glycosylation enzymes often leads to developmental defects and can influence various organismal behaviors such as stress and cognition. Thus, the complexity of glycan functions help to orchestrate proper neuronal development during embryogenesis, as well as influence behaviors in the adult organism.
The importance of glycosylation is further highlighted by defects in glycan structures that often lead to human disease, as exhibited by congenital disorders of glycosylation (CDG).25–29 These are usually inherited disorders resulting from defects in glycan biosynthesis, which are accompanied by severe developmental abnormalities, mental retardation, and difficulties with motor coordination. Such disorders highlight the importance of glycan biosynthesis in human health and development. Because therapeutic treatments are currently limited, investigations into the structure–activity relationships of glycans, as well as disease-associated alterations to glycan structure, are crucial for developing strategies to combat these diseases.
Understanding the structure–function relationships of glycans has been hampered by a lack of tools and methods to facilitate their analysis. In contrast to nucleic acids and proteins, oligosaccharides often have branched structures, and their biosynthesis is not template-encoded. As such, the composition and sequence of oligosaccharides cannot be easily predicted, and genetic manipulations are considerably less straightforward. Analytical techniques for investigating oligosaccharide composition, sequence, and tertiary structure are still undergoing development and are far from routine, unlike methods for DNA and protein analysis. Lastly, glycan structures are not under direct genetic control and, thus, are often heterogeneous. This heterogeneity complicates structure–function analyses by traditional biochemical approaches that rely on the isolation and purification of glycans from natural sources.
The problems associated with oligosaccharide analysis have hindered efforts to understand the biology of oligosaccharides yet have given chemists a unique opportunity to develop new methods to overcome these challenges. The development of chemical tools for the analysis of glycan structure and function is essential to advance our understanding of the roles of glycoconjugates in regulating diverse biological processes. In this review, we will highlight the emerging area of glyconeurobiology with an emphasis on current chemical approaches for elucidating the biological functions of glycans in the nervous system
Glycan Engineering for Cell and Developmental Biology
Cell-surface glycans are a diverse class of macromolecules that participate in many key biological processes, including cell-cell communication, development, and disease progression. Thus, the ability to modulate the structures of glycans on cell surfaces provides a powerful means not only to understand fundamental processes but also to direct activity and elicit desired cellular responses. Here, we describe methods to sculpt glycans on cell surfaces and highlight recent successes in which artificially engineered glycans have been employed to control biological outcomes such as the immune response and stem cell fate
Synthetic probes of glycosaminoglycan function
Glycosaminoglycans (GAGs) participate in many critical biological processes by modulating the activities of a wide range of proteins, including growth factors, chemokines, and viral receptors. Recent studies using synthetic oligosaccharides and glycomimetic polymers have established the importance of specific structural determinants in controlling GAG function. These findings illustrate the power of synthetic molecules to elucidate glycan-mediated signaling events, as well as the prospect of further advancements to understand the roles of GAGs in vivo and explore their therapeutic potential
An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
176P/LINEAR is a member of the new cometary class known as main-belt comets
(MBCs). It displayed cometary activity shortly during its 2005 perihelion
passage that may be driven by the sublimation of sub-surface ices. We have
therefore searched for emission of the H2O 110-101 ground state rotational line
at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory on UT 8.78 August 2011,
about 40 days after its most recent perihelion passage, when the object was at
a heliocentric distance of 2.58 AU. No H2O line emission was detected in our
observations, from which we derive sensitive 3-sigma upper limits for the water
production rate and column density of < 4e25 molec/s and of < 3e10 cm^{-2},
respectively. From the peak brightness measured during the object's active
period in 2005, this upper limit is lower than predicted by the relation
between production rates and visual magnitudes observed for a sample of comets
by Jorda et al. (2008) at this heliocentric distance. Thus, 176P/LINEAR was
likely less active at the time of our observation than during its previous
perihelion passage. The retrieved upper limit is lower than most values derived
for the H2O production rate from the spectroscopic search for CN emission in
MBCs.Comment: 5 pages, 2 figures. Minor changes to match published versio
Hamiltonian and measuring time for analog quantum search
We derive in this study a Hamiltonian to solve with certainty the analog
quantum search problem analogue to the Grover algorithm. The general form of
the initial state is considered. Since the evaluation of the measuring time for
finding the marked state by probability of unity is crucially important in the
problem, especially when the Bohr frequency is high, we then give the exact
formula as a function of all given parameters for the measuring time.Comment: 5 page
Correlation between dielectric constant and chemical structure of sodium silicate glasses
Journal URL: http://jap.aip.org/jap/staff.js
Discovery of a TNF-α Antagonist Using Chondroitin Sulfate Microarrays
We report the first example of synthetic chondroitin sulfate (CS) microarrays to rapidly identify glycosaminoglycan−protein interactions and probe the specificity of proteins for distinct sulfation sequences. Using the microarrays, we identify a novel interaction between CS and TNF-α, a proinflammatory cytokine involved in rheumatoid arthritis, Crohn's disease, and psoriasis. Moreover, we demonstrate that CS-E tetrasaccharides and polysaccharides enriched in the CS-E sulfation motif can inhibit the activity of this therapeutically important cytokine. We anticipate that carbohydrate microarrays will accelerate our understanding of glycosaminoglycan−protein interactions and the role of sulfation in modulating physiological and disease states
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