Biomedical subjects

H Vogel

Publications and source records attributed to H Vogel.

At least 127 records · Page 7Linked to original sources

PubMed1998

Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?

The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.

Bacterial Chromatophores↗

PubMed1998

Retention of wild-type p53 in tumors from p53 heterozygous mice: reduction of p53 dosage can promote cancer formation.

Tumor suppressor genes are generally viewed as being recessive at the cellular level, so that mutation or loss of both tumor suppressor alleles is a prerequisite for tumor formation. The tumor suppressor gene, p53, is mutated in approximately 50% of human sporadic cancers and in an inherited cancer predisposition (Li-Fraumeni syndrome). We have analyzed the status of the wild-type p53 allele in tumors taken from p53-deficient heterozygous (p53+/-) mice. These mice inherit a single null p53 allele and develop tumors much earlier than those mice with two functional copies of wild-type p53. We present evidence that a high proportion of the tumors from the p53+/- mice retain an intact, functional, wild-type p53 allele. Unlike p53+/- tumors which lose their wild-type allele, the tumors which retain an intact p53 allele express p53 protein that induces apoptosis following gamma-irradiation, activates p21(WAF1/CIP1) and Mdm2 expression, represses PCNA expression (a negatively regulated target of wild-type p53), shows high levels of binding to oligonucleotides containing a wild-type p53 response element and prevents chromosomal instability as measured by comparative genomic hybridization. These results indicate that loss of both p53 alleles is not a prerequisite for tumor formation and that mere reduction in p53 levels may be sufficient to promote tumorigenesis.

Animals↗

PubMed1998

A miniaturized monolayer trough with variable surface area in the square-millimeter range.

A new simple concept for a miniaturized monolayer trough is described. The overall monolayer area in the expanded state is approximately 150 mm2 and can be reduced by a factor of 2. The surface area is a function of the shape of the meniscus formed by the subphase and is controlled by the amount of water in the monolayer trough. The controlled compression of monolayers to a desired area per molecule with simultaneous observation of the lateral distribution of fluorescently labeled molecules is shown. A biological reaction between a specific antibody and lipid anchored peptide demonstrates the feasibility of monolayer experiments, which require only very small quantities of substance (in the pmol range). This trough might also be a valuable tool for the 2D crystallization of proteins at lipid layers via specific binding sites such as metal chelators.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1998

Friction anisotropy and asymmetry of a compliant monolayer induced by a small molecular tilt

Lateral force microscopy in the wearless regime was used to study the friction behavior of a lipid monolayer on mica. In the monolayer, condensed domains with long-range orientational order of the lipid molecules were present. The domains revealed unexpectedly strong friction anisotropies and non-negligible friction asymmetries. The angular dependency of these effects correlated well with the tilt direction of the alkyl chains of the monolayer, as determined by electron diffraction and Brewster angle microscopy. The molecular tilt causing these frictional effects was less than 15 degrees, demonstrating that even small molecular tilts can make a major contribution to friction.

Journal Article↗

PubMed1998

Screening ligands for membrane protein receptors by total internal reflection fluorescence: the 5-HT3 serotonin receptor.

The screening of ligands for membrane receptor proteins is central to the discovery of new pharmaceutical drugs. We present a general method to reversibly attach receptor proteins via an affinity tag to a quartz surface and subsequently detect with high sensitivity the real-time binding of ligands by total internal reflection fluorescence. A serotonin-gated ion channel protein was immobilized, and the binding of a fluorescent ligand was investigated. The affinity and the kinetic parameters of binding were measured, and the effect of unlabeled compounds was determined by competition. The pharmacology of the immobilized receptor was identical to that of the native receptor. The affinity of unlabeled ligands was rapidly and effectively determined. The method described here is generally applicable for membrane proteins and opens new ways for the discovery of pharmacologically active compounds.

Animals↗

PubMed1998

Incorporation of rhodopsin in laterally structured supported membranes: observation of transducin activation with spatially and time-resolved surface plasmon resonance.

Rhodopsin-transducin coupling was used as an assay to investigate a laterally patterned membrane reconstituted with a receptor and its G protein. It served as a model system to show the feasibility to immobilize G protein-coupled receptors on solid supports and investigate receptor activation and interaction with G proteins by one-dimensional imaging surface plasmon resonance. Supported membranes were formed by the self-assembly of lipids and rhodopsin from detergent solution onto functionalized gold surfaces. They formed micrometer-sized alternating regions of pure fluid phospholipid bilayers separated by bilayers composed of an outer phospholipid leaflet on a gold-attached inner thiolipid. Rhodopsin was found to incorporate preferentially into the phospholipid bilayer regions, whereas transducin was uniformly distributed over the entire outer surface of the supported patterned membrane. The influence of rhodopsin on the dark binding of transducin to lipid membranes was described quantitatively and compared with previously published data. Coupling reactions with transducin resembled closely the native system, indicating that the native functionality of rhodopsin was preserved in the supported membranes. The spatially varying properties of the membranes resulted in a pattern of rhodopsin activity on the surface. This combination of techniques is very promising for the investigation of the lateral diffusion of transducin, can be extended to include signalling proteins downstream of the G protein, and may be applied to functional screening of other G protein-coupled receptors. In the future, it may also serve as a basis for constructing biosensors based on receptor proteins.

Biosensing Techniques↗

PubMed1998

Brain electrical source analysis of primary cortical components of the tibial nerve somatosensory evoked potential using regional sources.

Tibial nerve somatosensory evoked potentials (SEPs) show higher amplitudes ipsilateral to the side of stimulation, whereas subdural recordings revealed a source in the foot area of the contralateral hemisphere. We now investigated this paradoxical lateralization by performing a brain electrical source analysis in the P40 time window (34-46 ms). The tibial nerve was stimulated behind the ankle (8 subjects). On each side, 2048 stimuli were applied twice. SEPs were recorded using 32 magnetic resonance imaging (MRI)-verified electrode positions (bandpass 0.5-500 Hz). In each case, the P40 amplitude was higher ipsilaterally (0.45 +/- 0.14 microV) than contralaterally (-0.49 +/- 0.16 microV). The best fitting regional source, however, was always located in the contralateral hemisphere with a mean distance of 8.2 +/- 4.3 mm from the midline. The positivity pointed ipsilaterally shifting from a frontal orientation (P37) to a parietal direction (P40). The P40 dipole moment was 2.5 times stronger than the dipole moment of P37, which makes P40 most prominent in EEG recordings. However, with its oblique dipole orientation compared to the tangential P37 dipole, it is systematically underestimated in MEG. Dipole orientations explained interindividual variability of scalp potential distribution. SEP amplitudes were smaller when generated in the dominant (left) hemisphere. This is explained by deeper located sources (5.4 +/- 1.6 mm) with a more tangential orientation (delta theta = 17.5 +/- 2.3 degrees) in the left hemisphere.

Adult↗

PubMed1998

Characterization of a mouse serotonin 5-HT3 receptor purified from mammalian cells.

A serotonin 5-HT3 receptor was functionally expressed to high levels and on a large scale in mammalian cells with the Semliki Forest virus system. Conditions were optimized to maximize detergent solubilization of the receptor, while preserving ligand binding activity. An efficient one-step purification yielding approximately 50% of the histidine-tagged 5-HT3 receptor was achieved with immobilized metal ion chromatography. The expressed receptor, in both membranes and purified preparations, exhibited wild-type ligand binding properties, characterized by one class of binding sites. The purity of the receptor was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, yielding a single band at 65 kDa, and was confirmed by the specific ligand binding activity of approximately 5 nmol/mg of protein. Deglycosylation of the receptor reduced the estimated relative molecular mass to 49 kDa. The apparent molecular mass of the functional receptor complex was determined by size exclusion chromatography to be 280 kDa, suggesting that the 5-HT3 receptor is a pentameric homooligomer. The secondary structure of the 5-HT3 receptor as determined by circular dichroism appeared to consist of mainly alpha-helices (50%) and beta-strands (24%), with minor contributions from nonregular structure (9%). The binding of either agonist or antagonist did not alter the secondary structure of the receptor.

Animals↗

PubMed1998

Embryonic lethality and tumorigenesis caused by segmental aneuploidy on mouse chromosome 11.

Chromosome engineering in mice enables the construction of models of human chromosomal diseases and provides key reagents for genetic studies. To begin to define functional information for a small portion of chromosome 11, deficiencies, duplications, and inversions were constructed in embryonic stem cells with sizes ranging from 1 Mb to 22 cM. Two deficiencies and three duplications were established in the mouse germline. Mice with a 1-Mb duplication developed corneal hyperplasia and thymic tumors, while two different 3- to 4-cM deficiencies were embryonically lethal in heterozygous mice. A duplication corresponding to one of these two deficiencies was able to rescue its haplolethality.

Aneuploidy↗

PubMed1998

Inclusion body myositis--a review.

Inclusion body myositis (IBM), a sporadic inflammatory myopathy, is the most frequently occurring progressive myopathy in adults older than 55 years. It more commonly affects men and usually is clinically and pathologically distinguishable from dermatomyositis or polymyositis. Muscle biopsy specimens will display inflammation in virtually all cases of sporadic IBM, along with rimmed vacuoles accompanied by the accumulation of beta-amyloid and other substances similar to those found in the degenerating neurons of Alzheimer's disease. The similarities between IBM and other inflammatory myopathies may contribute to its low level of diagnosis by pathologists. The proper recognition of IBM is important because, unlike other inflammatory myopathies, IBM is unresponsive to anti-inflammatory drugs.

Actin Cytoskeleton↗

PubMed1998

[Introduction of the Bavarian Scientific Rehabilitation Group].

As a part of the Rehabilitation Research Programme of both the Ministry for Education, Science, Research and Technology and the German Pension Insurance, the Rehabilitation Research Network of Bavaria has begun its work after having completed a planning phase of three years. Under the heading entitled "Patients in Rehabilitation" physical, psychological and social consequences of chronic diseases are addressed from a bio-psycho-social point of view. The network contains ten research projects which are located in different university institutions and rehabilitation clinics all over Bavaria. These projects can be assigned to three thematic clusters: diagnostical and predictor studies; evaluation of treatments; interface problems in rehabilitation. The interventions to be evaluated are aimed at strengthening patients' coping abilities. Wherever feasable, randomized controlled studies are performed. Both economical and gender-specific effects are investigated. A central facility for coordination and methodological consultation was implemented at the University of Würzburg. The network has the objective of both improving the quality of rehabilitation research and education and increasing the resources of institutions doing rehabilitation research in Bavaria.

Forecasting↗

PubMed1998

[Roentgen diagnosis without medical indications and physical injury. Verdict of the federal court 3 December 1997--2 StR 397/97].

An orthopedist had been sentenced for different offenses to two years and six months imprisonment by the Landgericht Frankfurt (superior court). One point of the ruling had been the evaluation of the use of X-ray methods without medical indication, which the Landgericht Frankfurt/Main (superior court) finally did not evaluate as bodily harm. The Bundesgerichtshof (supreme court) of Germany overruled this interpretation and referred the case back for new trial and ruling.

Germany↗

PubMed1998

[Barium aspiration with fatal outcome].

A female patient died after aspiration of a barium-containing contrast medium as a result of ARDS in spite of intensive medical care. In cases of aspiration, the degree of aspiration should be documented by X-ray as soon as possible in order to decide upon the extent of specific suction measure. Lethalities after aspiration may be more frequent than can be assumed from the reports in the literature.

Barium Sulfate↗

PubMed1997

Antibody binding to a functionalized supported lipid layer: a direct acoustic immunosensor.

A direct immunosensor has been developed using an acoustic wave device as a transducer. The device is based on an acoustic waveguide geometry that supports a Love wave. The biorecognition surface, formed on a gold layer, consisted of a biotinylated supported lipid layer which specifically bound streptavidin and, subsequently, biotinylated goat IgG. The modified surface was used as a model immunosensor and successfully detected rabbit anti-goat IgG in the concentration range 3 x 10(-8) - 10(-6) M. Using the anti-goat IgG binding isotherm and the time-resolved measurements of antibody binding, both the binding and rate constants of the reaction were determined. The specificity of each binding step was studied with the acoustic wave device, and it was concluded that the phospholipid bilayer showed a good suppression of nonspecific binding. Comparative measurements using surface plasmon resonance allowed the response of the immunosensor to be quantitatively correlated with mass binding to the surface.

Acoustic Stimulation↗

PubMed1997

Incorporation and Antibody Recognition of a Lipid-Anchored Membrane Protein in Supported Lipid Layers

The formation of supported lipid layers incorporating promastigote surface protease (PSP), a glycosylphosphatidylinositol-anchored protein, is investigated using surface plasmon resonance. Both hydrophilic and hydrophobic substrates are used for the formation of lipid layers, and results are consistent with the formation of lipid bilayers and monolayers, respectively. Specific antibody binding to layers containing PSP is observed, whereas nonspecific binding of the antibody to the surface is effectively suppressed by the phosphatidylcholine lipid layer. Phosphatidylinositol-specific phospholipase C is used to remove the lipid moieties from the membrane-incorporated PSP, releasing it into solution in a hydrophilic form and demonstrating that a large fraction of the protein is anchored in the lipid layer via the lipid moieties. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1997

Reversible oriented surface immobilization of functional proteins on oxide surfaces.

Reversible and oriented immobilization of proteins in a functionally active form on solid surfaces is a prerequisite for the investigation of molecular interactions by surface-sensitive techniques. We demonstrate a method generally applicable for the attachment of proteins to oxide surfaces. A nitrilotriacetic acid group serving as a chelator for transition metal ions was covalently bound to the surface via silane chemistry. Reversible binding of the green fluorescent protein, modified with a hexahistidine extension, was monitored in situ using total internal reflection fluorescence. The association constant and kinetic parameters of the binding process were determined. The reversible, directed immobilization of proteins on surfaces as described here opens new ways for structural investigation of proteins and receptor-ligand interactions.

Chelating Agents↗

PubMed1997

Formation of stable polypeptide monolayers at interfaces: controlling molecular conformation and orientation.

The molecular self-organization and structural properties of peptide assemblies at different interfaces, using either amphipathic or hydrophobic polypeptide helices, is described. The two peptides under investigation form stable monolayers on the water surface under the conservation of their molecular conformation, as studied by circular dichroism and polarization-modulation Fourier transform infrared (FTIR) spectroscopy. Using surface plasmon resonance and reflection-absorption FTIR, we show that such molecular layers can be transferred unaltered to solid substrates. Most importantly, the molecular orientation of the hydrophobic helices on solid supports such as gold can be controlled by choosing a particular procedure for the layer formation. The helices were oriented parallel to the interface in Langmuir-Blodgett monolayers, and perpendicular to the interface in self-assembled monolayers. Our reflection-absorption FTIR measurements have delivered for the first time direct experimental evidence for the molecular conformation and orientation of pure peptide monolayers. Suitable reference spectra of polypeptides with defined conformation and orientation are necessary to use this technique for the determination of the molecular orientation of peptides in monomolecular films. We have solved the problem for alpha-helical polypeptides by using bacteriorhodopsin as a reference in combination with synthetic alpha-helices of defined interfacial orientation. The present study shows the possibility of constructing immobilized peptide monolayers with predefined macroscopic properties and molecular structure by choosing the proper polypeptide amino acid sequence, the technique used for layer formation, and the supporting surface properties.

Amino Acid Sequence↗

PubMed1997

Cytogenetic analysis of 120 primary pediatric brain tumors and literature review.

We report chromosome results from 108 pediatric central nervous system (CNS) tumors. From our data and those in the literature we found that (1) cerebellar and low-grade astrocytic tumors, including gangliogliomas, are most often karyotypically normal; (2) supratentorial tumors were more frequently high-grade tumors that demonstrated a complex karyotype. Chromosome abnormalities were similar to those described in adult astrocytic tumors, namely, +7, 9p abnormalities, and -10; (3) primitive neuroectodermal tumors (PNETs) were virtually always karyotypically abnormal with a high frequency of +7, -8, i(17q), and -22. PNETs with -22 may represent a subset of tumors; (4) typical choroid plexus papillomas showed a normal karyotype, atypical papillomas showed a hyperdiploid karyotype (with +7, +12, and +20), choroid plexus carcinomas showed a hyperhaploid karyotype; (5) a few ependymomas showed hyperdiploidy or hypertetraploidy; (6) germ cell tumors showed complicated karyotypes; (7) monosomy 22 or 22q abnormalities appear to be a recurring finding in the malignant rhabdoid tumors; and (8) meningiomas showed -22 or 22q abnormalities associated with a complex karyotype. In general, in pediatric CNS tumors the least differentiated neoplasms have the greatest number of cytogenetic abnormalities. However, our present morphologic criteria for tumor diagnosis do not always correlate with a consistent karyotype, and further study of pediatric brain tumor morphology, site, behavior, and karyotype is required.

Astrocytoma↗