Proteoglykane und die Verpackung von Exportproteinen: Interaction von Serglycin und ZG 16 in den Zymogengranula des exokrinen Rattenpankreas

In Vorarbeiten konnte das Proteoglykan Serglycin in den Zymogengranula der Azinuszellen des exokrinen Rattenpankreas als Bindungspartner des sekretorischen Lektins ZG 16 identifiziert werden. Ferner konnte gezeigt werden, dass das korrekt glykosylierte Serglycin für die Sortierung von Zymogenen in die Granula nötig ist (Biederbick et al., 2003). Ziel dieser Arbeit war es, die Interaktion zwischen dem überwiegend membranständigen ZG 16 und Serglycin näher zu analysieren, um Aufschluss über Mechanismen der Verpackung und Sortierung der Zymogene zu erhalten. Darüber hinaus sollten mögliche weitere Proteoglykane aus dem Inhalt der Zymogengranula isoliert werden. Es wurden folgende Ergebnisse erzielt: 1. Durch Klonierung und Expression der unverzuckerten, rekombinanten N- und C-terminalen Abschnitte des Serglycin und deren Einsatz in Bindungsstudien (Co-Immunopräzipitation, GST-pull-down, Ligandenblots und Crosslinkexperimenten) wurde festgestellt, dass die Interaktion zwischen ZG 16 und Serglycin über den unverzuckerten N-terminalen Bereich (SGN) durch zuckerunabhängige Protein-Protein-Wechselwirkungen erfolgt. 2. Die Bindungssequenz des Serglycin an das ZG 16 konnte durch Herstellung verschiedener Punkt- und Deletionsmutanten des N-terminalen Bereichs SGN und deren Verwendung in Bindungsstudien auf die 9 N-Terminus nahen Aminosäuren ARYQWVRCK eingegrenzt werden. 3. Bei der Analyse der hypothetischen Sekundärstruktur des Serglycin, die mit Hilfe des ExPASy Molecular Biology Server erstellt wurde, gab es sehr starke Hinweise darauf, dass das Bindungsmotiv des Serglycin an das ZG 16 ein b-Faltblatt darstellt. Diese Daten zeigen, dass Serglycin über den N-terminalen unverzuckerten Abschnitt eine Protein-Protein-Interaktion mit dem sekretorischen Lektin ZG 16 macht. Über diese Interaktion werden das Serglycin und über seine Glykosaminoglykan-Ketten assoziierte Zymogene an die Zymogengranulamembran gebunden. Diese Wechselwirkung stellt einen Sortierungsmechanismus für die Zymogene in die Granula dar. 4. Für das Vorhandensein weiterer Proteoglykane im Inhalt der Zymogengranula (ZGI) konnten nur indirekte Hinweise gefunden werden. Im Blyscan-Assay, einer Fällung, die spezifisch für Proteoglykane ist, konnten durch Extinktionsmessung Proteoglykane nachgewiesen werden. Die größte Extinktion wurde nach Vorbehandlung des ZGI mit NaHCO3 erhalten. 5. Die Zymogene scheinen mit Proteoglykanen assoziiert zu sein. Durch diese Interaktion gelangt ein Teil der Zymogene noch nach NaHCO3-Behandlung von ZGI und anschließender Blyscan- oder Wesselfällung in das Blyscanpellet, bzw. in die organische Phase der Wesselfällung. Durch EGTA-Inkubation von ZGI kann diese Interaktion zwischen Proteoglykanen und Zymogenen aufgehoben werden. Hier erscheinen keine Zymogene im Blyscanpellet oder der organischen Phase der Wesselfällung

The prismatic Sigma 3 (10-10) twin bounday in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy

The microscopic structure of a prismatic $\Sigma 3$ $(10\bar{1}0)$ twin boundary in \aal2o3 is characterized theoretically by ab-initio local-density-functional theory, and experimentally by spatial-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM), measuring energy-loss near-edge structures (ELNES) of the oxygen $K$-ionization edge. Theoretically, two distinct microscopic variants for this twin interface with low interface energies are derived and analysed. Experimentally, it is demonstrated that the spatial and energetical resolutions of present high-performance STEM instruments are insufficient to discriminate the subtle differences of the two proposed interface variants. It is predicted that for the currently developed next generation of analytical electron microscopes the prismatic twin interface will provide a promising benchmark case to demonstrate the achievement of ELNES with spatial resolution of individual atom columns

Collective Sideband Cooling in an Optical Ring Cavity

We propose a cavity based laser cooling and trapping scheme, providing tight confinement and cooling to very low temperatures, without degradation at high particle densities. A bidirectionally pumped ring cavity builds up a resonantly enhanced optical standing wave which acts to confine polarizable particles in deep potential wells. The particle localization yields a coupling of the degenerate travelling wave modes via coherent photon redistribution. This induces a splitting of the cavity resonances with a high frequency component, that is tuned to the anti-Stokes Raman sideband of the particles oscillating in the potential wells, yielding cooling due to excess anti-Stokes scattering. Tight confinement in the optical lattice together with the prediction, that more than 50% of the trapped particles can be cooled into the motional ground state, promise high phase space densities.Comment: 4 pages, 1 figur

First-principles study of spontaneous polarization in multiferroic BiFeO3_3

The ground-state structural and electronic properties of ferroelectric BiFeO$_3$ are calculated using density functional theory within the local spin-density approximation and the LSDA+U method. The crystal structure is computed to be rhombohedral with space group $R3c$, and the electronic structure is found to be insulating and antiferromagnetic, both in excellent agreement with available experiments. A large ferroelectric polarization of 90-100 $\mu$C/cm$^2$ is predicted, consistent with the large atomic displacements in the ferroelectric phase and with recent experimental reports, but differing by an order of magnitude from early experiments. One possible explanation is that the latter may have suffered from large leakage currents. However both past and contemporary measurements are shown to be consistent with the modern theory of polarization, suggesting that the range of reported polarizations may instead correspond to distinct switching paths in structural space. Modern measurements on well-characterized bulk samples are required to confirm this interpretation.Comment: (9 pages, 5 figures, 5 tables

Electronic structure and total energy of interstitial hydrogen in iron: Tight binding models

An application of the tight binding approximation is presented for the description of electronic structure and interatomic force in magnetic iron, both pure and containing hydrogen impurities. We assess the simple canonical d-band description in comparison to a non orthogonal model including s and d bands. The transferability of our models is tested against known properties including the segregation energies of hydrogen to vacancies and to surfaces of iron. In many cases agreement is remarkably good, opening up the way to quantum mechanical atomistic simulation of the effects of hydrogen on mechanical properties

Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits

We analyze two configurations for laser cooling of neutral atoms whose internal states store qubits. The atoms are trapped in an optical lattice which is placed inside a cavity. We show that the coupling of the atoms to the damped cavity mode can provide a mechanism which leads to cooling of the motion without destroying the quantum information.Comment: 12 page

Dark matter powered stars: Constraints from the extragalactic background light

The existence of predominantly cold non-baryonic dark matter is unambiguously demonstrated by several observations (e.g., structure formation, big bang nucleosynthesis, gravitational lensing, and rotational curves of spiral galaxies). A candidate well motivated by particle physics is a weakly interacting massive particle (WIMP). Self-annihilating WIMPs would affect the stellar evolution especially in the early universe. Stars powered by self-annihilating WIMP dark matter should possess different properties compared with standard stars. While a direct detection of such dark matter powered stars seems very challenging, their cumulative emission might leave an imprint in the diffuse metagalactic radiation fields, in particular in the mid-infrared part of the electromagnetic spectrum. In this work the possible contributions of dark matter powered stars (dark stars; DSs) to the extragalactic background light (EBL) are calculated. It is shown that existing data and limits of the EBL intensity can already be used to rule out some DS parameter sets.Comment: Accepted for publication in ApJ; 7 pages, 5 figure

Statistical anisotropy of magnetohydrodynamic turbulence

Direct numerical simulations of decaying and forced magnetohydrodynamic (MHD) turbulence without and with mean magnetic field are analyzed by higher-order two-point statistics. The turbulence exhibits statistical anisotropy with respect to the direction of the local magnetic field even in the case of global isotropy. A mean magnetic field reduces the parallel-field dynamics while in the perpendicular direction a gradual transition towards two-dimensional MHD turbulence is observed with $k^{-3/2}$ inertial-range scaling of the perpendicular energy spectrum. An intermittency model based on the Log-Poisson approach, $\zeta_p=p/g^2 +1 -(1/g)^{p/g}$, is able to describe the observed structure function scalings.Comment: 4 pages, 3 figures. To appear in Phys.Rev.

Differential expression and sex chromosome association of CHD3/4 and CHD5 during spermatogenesis

ATP-dependent nucleosome remodelers of the CHD family play important roles in chromatin regulation during development and differentiation. The ubiquitously expressed CHD3 and CHD4 proteins are essential for stem cell function and serve to orchestrate gene expression in different developmental settings. By contrast, the closely related CHD5 is predominantly expressed in neural tissue and its role is believed to be restricted to neural differentiation. Indeed, loss of CHD5 contributes to neuroblastoma. In this study, we first demonstrate that CHD5 is a nucleosome-stimulated ATPase. We then compare CHD3/4 and CHD5 expression in mouse brain and show that CHD5 expression is restricted to a subset of cortical and hippocampal neurons whereas CHD3/4 expression is more widespread. We also uncover high levels of CHD5 expression in testis. CHD5 is transiently expressed in differentiating germ cells. Expression is first detected in nuclei of postmeiotic round spermatids, reaches a maximum in stage VIII spermatids and then falls to undetectable levels in stage IX spermatids. Surprisingly, CHD3/4 and CHD5 show complementary expression patterns during spermatogenesis with CHD3/ 4 levels progressively decreasing as CHD5 expression increases. In spermatocytes, CHD3/4 localizes to the pseudoautosomal region, the X centromeric region and then spreads into the XY body chromatin. In postmeiotic cells, CHD5 colocalises with macroH2A1.2 in association with centromeres and part of the Y chromosome. The subnuclear localisations of CHD4 and CHD5 suggest specif

Specificity protein 2 (Sp2) is essential for mouse development and autonomous proliferation of mouse embryonic fibroblasts

Background: The zinc finger protein Sp2 (specificity protein 2) is a member of the glutamine-rich Sp family of transcription factors. Despite its close similarity to Sp1, Sp3 and Sp4, Sp2 does not bind to DNA or activate transcription when expressed in mammalian cell lines. The expression pattern and the biological relevance of Sp2 in the mouse are unknown. Methodology/Principal Findings: Whole-mount in situ hybridization of mouse embryos between E7.5 and E9.5 revealed abundant expression in most embryonic and extra-embryonic tissues. In order to unravel the biological relevance of Sp2, we have targeted the Sp2 gene by a tri-loxP strategy. Constitutive Sp2null and conditional Sp2cko knockout alleles were obtained by crossings with appropriate Cre recombinase expressing mice. Constitutive disruption of the mouse Sp2 gene (Sp2null) resulted in severe growth retardation and lethality before E9.5. Mouse embryonic fibroblasts (MEFs) derived from Sp2null embryos at E9.5 failed to grow. Cre-mediated ablation of Sp2 in Sp2cko/cko MEFs obtained from E13.5 strongly impaired cell proliferation. Conclusions/Significance: Our results demonstrate that Sp2 is essential for early mouse development and autonomous proliferation of MEFs in culture. Comparison of the Sp2 knockout phenotype with th