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A Wegner

Publications and source records attributed to A Wegner.

At least 19 recordsLinked to original sources
PubMed2006

P2 receptor-stimulation influences axonal outgrowth in the developing hippocampus in vitro.

Extracellular ATP might act as a trophic factor on growing axons during development of the CNS via P2 receptors. In the present study the postnatal presence of selected P2 receptor subtypes was analyzed and their putative trophic capacity in entorhino-hippocampal slice co-cultures of mouse brain was tested. The effect of the P2 receptor ligands 2-methylthioadenosine-5'-triphosphate (P2X/Y receptor agonist) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (P2X/Y receptor antagonist) on axonal growth and fiber density of biocytin-labeled hippocampal projections was compared both with untreated cultures and with cultures treated with artificial cerebrospinal fluid. After 10 days in vitro, double immunofluorescence labeling revealed the expression of P2X(1), P2X(2), P2X(4) as well as P2Y(1) and P2Y(2) receptors in the examined regions of entorhinal fiber termination. Further, quantitative analysis of identified biocytin-traced entorhinal fibers showed a significant increase in fiber density in the dentate gyrus after incubation of the slices with the P2 receptor agonist 2-methylthioadenosine-5'-triphosphate. This neurite outgrowth promoting effect was completely abolished by the P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid. Our in vitro data indicate that ATP via its P2X and P2Y receptors can shape hippocampal connectivity during development.

Adenosine Triphosphate↗
PubMed2001

The di-aromatic pentapeptide repeats of the human peroxisome import receptor PEX5 are separate high affinity binding sites for the peroxisomal membrane protein PEX14.

PEX5 functions as a mobile import receptor for peroxisomal matrix proteins with a peroxisomal targeting signal 1 (PTS1). A critical step within the PTS1-import pathway is the interaction between PEX5 and the peroxisome membrane-associated protein PEX14. Based on two-hybrid analyses in mammalian cells and complementary in vitro binding assays, we demonstrate that the evolutionarily conserved pentapeptide repeat motifs, WX(E/D/Q/A/S)(E/D/Q)(F/Y), in PEX5 bind to PEX14 with high affinity. The results obtained indicate that each of the seven di-aromatic pentapeptides of human PEX5 interacts separately at the same binding site in the N terminus of PEX14 with equilibrium dissociation constants in the low nanomolar range. Mutational analysis of the PEX14-binding motifs reveals that the conserved aromatic amino acids at position 1 or 5 are essential for high affinity binding. We propose that the side chains of the aromatic amino acids are in close proximity as part of an amphipathic alpha-helix and together form hydrophobic anchors for binding PEX5 to individual PEX14 molecules.

Amino Acid Motifs↗
PubMed2000

Tetrachloro- and tetrabromoarsonium(V) cations: raman and 75As, 19F NMR spectroscopic characterization and X-ray crystal structures of [AsCl4][As(OTeF5)6] and [AsBr4][AsF(OTeF5)5] .

The salts [AsX4][As(OTeF5)6] and [AsBr4][AsF(OTeF5)5] (X = Cl, Br) have been prepared by oxidation of AsX3 with XOTeF5 in the presence of the OTeF5 acceptors As(OTeF5)5 and AsF(OTeF5)4. The mixed salts [AsCl4][Sb(OTeF5)6-nCl(n-2)] and [AsCl4][Sb(OTeF5)6-nCl(n)] (n > or = 2) have also been prepared. The AsBr4+ cation has been fully structurally characterized for the first time in SO2ClF solution by 75As NMR spectroscopy and in the solid state by a single-crystal X-ray diffraction study of [AsBr4][AsF(OTeFs)5]: P1, a = 9.778(4) A, b = 17.731(7) A, c = 18.870(8) A, alpha = 103.53(4)degrees, beta = 103.53(4) degrees, gamma = 105.10(4) degrees, V = 2915(2) A3, Z = 4, and R1 = 0.0368 at -183 degrees C. The crystal structure determination and solution 75As NMR study of the related [AsCl4][As(OTeF5)6] salt have also been carried out: [AsCl4][As(OTeF5)6], R3, a = 9.8741(14) A, c = 55.301(11) A, V= 4669(1) A3, Z = 6, and R1 = 0.0438 at -123 degrees C; and R3, a = 19.688(3) A, c = 55.264(11) A, V= 18552(5) A3, Z = 24, and R1 = 0.1341 at -183 degrees C. The crystal structure of the As(OTeF5)6- salt reveals weaker interactions between the anion and cation than in the previously known AsF6- salt. The AsF(OTeF5)5- anion is reported for the first time and is also weakly coordinating with respect to the AsBr4+ cation. Both cations are undistorted tetrahedra with bond lengths of 2.041(5)-2.056(3) A for AsCl4+ and 2.225(2)-2.236(2) A for AsBr4+. The Raman spectra are consistent with undistorted AsX4+ tetrahedra and have been assigned under Td point symmetry. The 35Cl/37Cl isotope shifts have been observed and assigned for AsCl4+, and the geometrical parameters and vibrational frequencies of all known and presently unknown PnX4+ (Pn = P, As, Sb, Bi; X = F, Cl, Br, I) cations have been calculated using density functional theory methods.

Journal Article↗
PubMed2000

Assessment of the adhesion quality of fusion-welded silicon wafers with nonlinear ultrasound

Diffusion bonded silicon wafers are employed in the semiconductor industry. Their bonding quality must be monitored by a nondestructive testing technique. We present an ultrasonic technique allowing us to monitor the quality of the diffusion bond by measuring the anharmonic content of a transmitted ultrasonic wave. The anharmonicity is caused by weak bonds and manifests itself at high dynamic strains exerted by the ultrasonic wave. The source of nonlinearity is located in the rim of delaminations in the interface.

Journal Article↗
PubMed2000

Gelsolin as a calcium-regulated actin filament-capping protein.

Various concentrations of gelsolin (25-100 nM) were added to 2 microM polymerized actin. The concentrations of free calcium were adjusted to 0.05-1.5 microM by EGTA/Ca2+ buffer. Following addition of gelsolin actin depolymerization was observed that was caused by dissociation of actin subunits from the pointed ends of treadmilling actin filaments and inhibition by gelsolin of polymerization at barbed ends. The time course of depolymerization revealed an initial lag phase that was followed by slow decrease of the concentration of polymeric actin to reach the final steady state polymer and monomer concentration. The initial lag phase was pronounced at low free calcium and low gelsolin concentrations. On the basis of quantitative analysis the kinetics of depolymerization could be interpreted as capping, i.e. binding of gelsolin to the barbed ends of actin filaments and subsequent inhibition of polymerization, rather than severing. The main argument for this conclusion was that even gelsolin concentrations (100 nM) that exceed the concentration of filament ends ( approximately 2 nM), cause the filaments to depolymerize at a rate that is similar to the rate of depolymerization of the concentration of pointed ends existing before addition of gelsolin. The rate of capping is directly proportional to the free calcium concentration. These experiments demonstrate that at micromolar and submicromolar free calcium concentrations gelsolin acts as a calcium-regulated capping protein but not as an actin filament severing protein, and that the calcium binding sites of gelsolin which regulate the various functions of gelsolin (capping, severing and monomer binding), differ in their calcium affinity.

Actin Depolymerizing Factors↗
PubMed1999

Co-operative binding of Ca2+ ions to the regulatory binding sites of gelsolin.

The rate of association of actin with gelsolin was measured at various Ca2+ and ATP concentrations. The fraction of Ca2+-activated gelsolin was determined by quantitative evaluation of the association rates thereby assuming that Ca2+-binding gelsolin associates with actin and Ca2+-free gelsolin does not. A plot of the fraction of Ca2+-activated gelsolin vs. the free Ca2+ concentration revealed a sigmoidal shape suggesting that co-operative binding of Ca2+ ions is required for activation of gelsolin. A good fit of the experimental data by calculated binding curves was obtained if two Ca2+ ions were assumed to bind to actin in a highly co-operative manner. ATP decreased the rate of association of gelsolin with actin and bound to gelsolin at a low affinity (Kd = 32 microm for Ca2+-free and Kd = 400 microm for Ca2+-activated gelsolin). In contrast, a 1 : 1 gelsolin-actin complex was found to be activated for association with actin by a single Ca2+ ion in a non-co-operative manner.

Actins↗
PubMed1998

Kinetic evidence for a readily exchangeable nucleotide at the terminal subunit of the barbed ends of actin filaments.

The time course of actin depolymerization was quantitatively analyzed to obtain insight into the reactions occurring during actin disassembly. Polymeric actin was diluted, and subsequently the time course of depolymerization was measured. In the presence of 0.5 mM ATP, 100 mM KCl, and 1 mM MgCl2, continuous depolymerization was observed both when the filaments were carefully diluted and when the filaments were fragmented to produce short filaments. The rates of the reactions that are known to occur during depolymerization, such as dissociation and association of ADP- and ATP-actin molecules and exchange of nucleotides bound to monomeric actin, were determined by independent experiments. When the determined rate parameters were used to calculate the time course of depolymerization, consistently in the simulations fast depolymerization of ADP-actin was followed by slower polymerization of ATP-actin that was formed from ADP-actin by nucleotide exchange. The lack of fast depolymerization and subsequent slower polymerization in the experiments suggests that our present conception about actin disassembly requires modification. Good agreement of calculated time courses with the experimentally determined continuous depolymerization was achieved if ADP bound to the terminal subunit of barbed filament ends was assumed to be readily exchangeable for ATP. Fast nucleotide exchange at terminal subunits may contribute to the stability of barbed filament ends and to their role as polymerizing ends in living cells.

Actin Depolymerizing Factors↗
PubMed1998

Derivation of insertin.

Insertin is an actin-binding protein that has been isolated from chicken gizzard smooth muscle that has been shown to be highly homologous to amino acids 962-1292 of tensin [Weigt et al., 1992]. Because of the high homology, we investigated the question whether the mRNAs of insertin and of tensin are derived from the same gene by alternative splicing, whether insertin and tensin are encoded by two different genes, or whether insertin is a proteolytic fragment of tensin. In a Northern blot analysis, mRNA from chicken gizzard was hybridized with oligonucleotides specific for tensin and for the insertin domain of tensin. The tensin-specific oligonucleotide hybridized only with the previously reported 8- and 10-kbp RNAs. However, the insertin domain-specific oligonucleotide hybridized with a 1.2 and a 1.6 kbp RNA in addition to the 8 and 10 kbp RNA. The 1.2- and 1.6-kbp RNA occurred in small amounts, as compared with the 8- and 10-kbp RNA. Southern blot analysis of DNA cleaved by the restriction endonucleases BamH1 and HindIII demonstrated that only one gene for the insertin and tensin exists. Insertin isolated from chicken gizzard smooth muscle was investigated by mass spectrometry. The N-termini of three isolated peptides were found to begin at adjacent amino acids and were likely to be formed from tensin by proteolysis. The results suggest that, for insertin, an mRNA exists that is derived from one gene common for insertin and tensin. However, the insertin-specific mRNA contributes relatively little to expression of insertin domains in cells. Insertin preparations from chicken gizzard contain mainly insertin domains formed from tensin by proteolysis.

Amino Acid Sequence↗
PubMed1998

[Teleconsultation network for ophthalmology--experiences and results].

MOTIVATION: Telemedical services for ophthalmology are developed within the OPHTEL project, which has been funded by the European Union and by the Bavarian government in the Bavaria-online initiative. METHODS: Seven private ophthalmologists, one university eye clinic, one clinical Diabetes center and an informatics research institute are connected within a teleconsultation network. Asynchronous (based on Internet E-Mail) and synchronous (based on ISDN-mediated videoconferencing tools) types of teleconsultations are realized. RESULTS: 86 teleconsultations (62 asynchronous, 23 synchronous) took place within the first 10 months. Complex and rare eye diseases as well as interdisciplinary questions (ophthalmology--diabetology) are the main area of medical communication interest. Legal and security problems are discussed. CONCLUSIONS: Telemedical services must be understood as a complete process of medical care on the basis of modern communication technologies, which influences also the management of this process.

Computer Communication Networks↗
PubMed1996

The rate of annealing of actin tropomyosin filaments depends strongly on the length of the filaments.

Actin tropomyosin filaments were sheared to produce short filaments. Following incubation for 0 to 10000 s annealing of the filaments was assayed by determination of the rate of polymerization of monomeric actin onto the filament ends. The rate of decrease of the concentration of filament ends was found to be proportional to its fourth power. In contrast, the rate of end-to-end association of actin filaments in the absence of tropomyosin was proportional to the square of the concentration of filament ends. The strong dependence on the filament length of the rate of annealing of actin tropomyosin filaments was interpreted by the model of Hill (Biophys. J., 44, 285-288 (1983)) who pointed out that the rate constant of end-to-end association of long rod-like filaments is expected to depend on the length of the filaments for sterical conditions.

Actins↗
PubMed1996

The end of a polymerizing actin filament contains numerous ATP-subunit segments that are disconnected by ADP-subunits resulting from ATP hydrolysis.

ATP hydrolysis by copolymers of ATP-actin and ADP-actin was investigated in order to analyze the effect of interfaces between ATP-subunits and ADP-subunits on hydrolysis of actin-bound ATP. Copolymers of ATP- and ADP-subunits were formed by polymerization of ATP- and ADP-actin monomers onto filaments. By changing the ratio of polymerizing ATP-actin monomers to ADP-actin monomers, the number of interfaces between ATP- and ADP-subunits and of ATP-subunits only surrounded by further ATP-subunits was varied. The rate of actin polymerization and of ATP hydrolysis was measured simultaneously on the same samples. The lag time between incorporation of actin monomers into filaments and subsequent ATP hydrolysis was found to be similar both for polymerized ATP-actin and for copolymers formed by various ratios of ATP- to ADP-actin. The experiments were performed in the presence of 1 mM MgCl2, 0.05 mM CaCl2, and 100 mM KCl or of 1 mM MgCl2, and 0.4 mM EGTA. The type of cations was found to have no major effect on the rate of ATP hydrolysis. A quantitative evaluation of the experimental data suggests that ATP at interfaces between ATP- and ADP-subunits is hydrolyzed not more than 10 times faster than ATP of subunits surrounded by further ATP-subunits. On the basis of these results, one can conclude that an actin filament onto which ATP-actin monoMers polymerize contains numerous segments of ATP-subunits that are disconnected by ADP-subunits resulting from ATP hydrolysis. The average length of the numerous ATP segments of a steadily polymerizing filament is in the range of 10 ATP-subunits or below.

Actins↗
PubMed1995

Coactosin interferes with the capping of actin filaments.

Coactosin, a 16 kDa protein associated with the actin cytoskeleton from Dictyostelium discoideum, was purified by an improved method, in which other components of the cytoskeleton were removed. The highly purified coactosin had no effect on the time course of actin polymerization, but when added to actin in presence of capping proteins, coactosin counteracted the capping activity of these proteins. The capping proteins cap32/34 and severin domain 1 retarded actin polymerization, on addition of coactosin to samples containing one of these capping proteins the time course of actin polymerization became close to controls without capping proteins.

Actins↗
PubMed1995

Two low-affinity Ca(2+)-binding sites of gelsolin that regulate association with actin.

The time course of binding of actin to gelsolin or 1:1 gelsolin-actin complex was measured at defined Ca2+ concentrations in the range 0.5-500 microM. The rate of association was followed by the fluorescence increase of a fluorescent label covalently linked to actin. Free Ca2+ was determined by titration with EGTA in the presence of Fura-2 as indicator. The experimental data were quantitatively evaluated by calculations of the kinetics of association of actin with gelsolin thereby taking into account the equilibrium of binding of Ca2+ ions to gelsolin. It was found that association of gelsolin with one actin monomer is regulated by a Ca(2+)-binding site with a dissociation constant Kd1 = 25 microM. Binding of the second actin monomer was found to be controlled by a Ca(2+)-binding site of which the dissociation constant Kd2 was 200 microM. Mg2+ ions in the concentration range 0-1 mM did not compete with Ca2+ for binding to gelsolin. More complex interactions of gelsolin with actin such as nucleated actin polymerization were found to occur even at Ca2+ concentrations below Kd1 (e.g. 10 microM) at almost maximal rates.

Actins↗
PubMed1994

Mechanism of ATP hydrolysis by polymeric actin.

The lag between polymerization of actin and ATP hydrolysis in actin filaments was analyzed in terms of the mechanism of the hydrolysis reaction. Under the experimental conditions (100 mM KCl and 1 mM MgCl2, or without KCl, 1 mM MgCl2 and 0.4 mM EGTA, 25 degrees C) ATP hydrolysis lagged behind polymerization by about 100 s independently of the concentration of polymerizing filament ends and of the actin monomer concentration. Three models of ATP hydrolysis were compared to experimental data: (i) Random ATP hydrolysis, ATP is assumed to be hydrolyzed at a rate that is independent of the type of the nucleotide bound to adjacent filament subunits. (ii) Cooperative hydrolysis, the rate of ATP hydrolysis is thought to depend on the type of nucleotide bound to adjacent subunits. (iii) Sequential hydrolysis, ATP is assumed to be hydrolyzed only at the interface between ATP-subunits and ADP-subunits. The model of sequential ATP hydrolysis could be excluded. The results were in agreement with random or cooperative ATP hydrolysis. The differences of the rates of ATP hydrolysis by a random or cooperative mechanism are so small that based on the experimental results no distinction between these two mechanisms could be made. All available evidence points towards a mechanism of ATP hydrolysis in which several or perhaps many interfaces between ATP- and ADP-subunits are formed within a filament.

Actins↗
PubMed1994

Nucleation of actin polymerization by gelsolin.

The time-course of assembly of actin with gelsolin was measured by the fluorescence increase of a fluorescent label covalently linked to actin. The actin concentrations ranged from values far below the critical concentration to values above the critical concentration of the pointed ends of actin filaments. If the concentration of actin was in the range of the critical monomer concentration (0.64 microM), the time-course of the concentration of actin assembled with gelsolin revealed a sigmoidal shape. At higher actin concentrations the time-course of association of actin with gelsolin approximated an exponential curve. The measured time-courses of assembly were quantitatively interpreted by kinetic rate equations. A poor fit was obtained if two actin molecules were assumed to bind to gelsolin to form a 1:2 gelsolin-actin complex and subsequently further actin molecules were assumed to polymerize onto the 1:2 gelsolin-actin complex toward the pointed end. A considerably better agreement between calculated and measured time-courses was achieved if additional creation of actin filaments by fast fragmentation of newly formed actin filaments by not yet consumed gelsolin was assumed to occur. This suggests that both polymerization of actin onto gelsolin and fragmentation of actin filaments contribute to formation of new actin filaments by gelsolin. Furthermore it could be demonstrated that below the critical monomer concentration appreciable amounts of actin are incorporated into gelsolin-actin oligomers.

Actins↗