Structural Instability of Ferromagnetic fcc Fe Films on Cu(100).
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
S Müller
Publications and source records attributed to S Müller.
Tetrabrachion: a filamentous archaebacterial surface protein assembly of unusual structure and extreme stability.
The surface (S-) layer of the hyperthermophilic archaebacterium Staphylothermus marinus was isolated, dissected into separate domains by chemical and proteolytic methods, and analyzed by spectroscopic, electron microscopic and biochemical techniques. The S-layer is formed by a poorly ordered meshwork of branched, filiform morphological subunits resembling dandelion seed-heads. A morphological subunit (christened by us tetrabrachion) consists of a 70 nm long, almost perfectly straight stalk ending in four straight arms of 24 nm length that provide lateral connectivity by end-to-end contacts. At 32 nm from the branching point, tetrabrachion carries two globular particles of 10 nm diameter that have both tryptic and chymotryptic protease activity. Tetrabrachion is built by a tetramer of M(r) 92,000 polypeptides that form a parallel, four-stranded alpha-helical rod and separate at one end into four strands. These strands interact in a 1:1 stoichiometry with polypeptides of M(r) 85,000 to form the arms. The arms are composed entirely of beta-sheets. All S-layer components contain bound carbohydrates (glucose, mannose, and glucosamine) at a ratio of 38 g/100 g protein for the complete tetrabrachion-protease complex. The unique structure of tetrabrachion is reflected in an extreme thermal stability in the presence of strong denaturants (1% (w/v) SDS of 6M guanidine): the arms, which are stabilized by intramolecular disulphide bridges, melt around 115 degrees C under non-reducing conditions, whereas the stalk sustains heating up to about 130 degrees C. Complete denaturation of the stalk domain requires treatment with 70% (v/v) sulfuric acid or with fuming trifluoromethanesulfonic acid. The globular protease can be heated to 90 degrees C in 6M guanidine and to 120 degrees C in 1% SDS and represents one of the most stable proteases characterized to date.
Archaea↗
Recovery from Wernicke's aphasia: a positron emission tomographic study.
Changes in the organization of the brain after recovery from aphasia were investigated by measuring increases in regional cerebral blood flow (rCBF) during repetition of pseudowords and during verb generation. Six right-handed patients who had recovered from Wernicke's aphasia caused by an infarction destroying the left posterior perisylvian language zone were compared with 6 healthy, right-handed volunteers. In the control subjects, strong rCBF increases were found in the left hemisphere in the posterior part of the superior and middle temporal gyrus (Wernicke's area), and during the generation task in lateral prefrontal cortex (LPFC) and in inferior frontal gyrus (Broca's area). There were some weak right hemisphere increases in superior temporal gyrus and inferior premotor cortex. In the patients, rCBF increases were preserved in the frontal areas. There was clear right hemisphere activation in superior temporal gyrus and inferior premotor and lateral prefrontal cortices, homotopic to the left hemisphere language zones. Increased left frontal and right perisylvian activity in patients with persisting destruction of Wernicke's area emphasizes redistribution of activity within the framework of a preexisting, parallel processing and bilateral network as the central mechanism in functional reorganization of the language system after stroke.
Aged↗
Platelet aggregation inhibiting and anticoagulant effects of oligoamines, XXIX: Influence of the antithrombotic oligoamine RE 1492 on the storage of red blood cells, morphology, their potassium and ATP content, hemolysis and viability.
The influence of RE 1492 on the storage of red blood cells (RBCs) was investigated. RE 1492 (c > or = 50 mumol/L) induces the formation of cup cells and hence delays the appearance of echinocytes and crenated spheres in the blood. A concentration of 50 mumol/L RE 1492 drops hemolysis by 50%. At this concentration after 6 h of storage the potassium efflux was enhanced significantly. The ATP concentration was decreased between 12 h and 24 h of storage. During the first 6 h these alterations have no effect on the in vivo viability of RBCs. After 12 h of storage a significant reduction in viability is observed. We suppose that the changes observed are due to the intercalation of RE 1492 in the phospholipid matrix of the RBC membrane, followed by an accelerated substrate turnover in the RBCs.
Adenosine Triphosphate↗
Cloning of ATAC, an activation-induced, chemokine-related molecule exclusively expressed in CD8+ T lymphocytes.
A cDNA clone, designated ATAC, was isolated from a collection of human T cell activation genes. Analysis of tissue distribution determined that ATAC mRNA of approximately 0.9 kb is exclusively expressed in activated CD8+ T cells. Induction of the ATAC gene requires stimulation by both phorbol 12-myristate 13-acetate and Ca2+ ionophore A23187 ("two-signal gene") and is fully abrogated by the immunosuppressive agent cyclosporin A. Upon stimulation, ATAC mRNA is detectable within 30 min, maximal expression is seen after 4 h. The polypeptide encoded by the open reading frame of ATAC mRNA is 114 amino acids long with a calculated M(r) of 12.52 kDa. The structural features predict the cleavage and secretion of a mature ATAC protein of approximately 10 kDa from the 12.52-kDa precursor. ATAC is highly similar to a very recently identified murine molecule designated lymphotactin both at the cDNA (73.8% identity) and the protein (61.4% identity) levels, and related to members of the C-C and C-X-C chemokine families. Two variants of the ATAC protein were expressed and tested for chemotaxis and Ca2+ release on a variety of target cells. The ATAC gene was located to chromosome 1q23.
Amino Acid Sequence↗
A soluble form of TRAP (CD40 ligand) is rapidly released after T cell activation.
TRAP is a tumor necrosis factor (TNF)-related, 33-kDa type II transmembrane protein almost exclusively expressed on the surface of activated CD4+ T lymphocytes. Interaction of TRAP with CD40 on B cells is of paramount importance for immunoglobulin class switching and subsequent synthesis of IgG, IgA or IgE in vivo. We now provide evidence that activated T cells not only express cell membrane-associated TRAP but also a soluble form of TRAP (sTRAP). After generating monoclonal antibodies against TRAP and establishing a TRAP-specific enzyme-linked immunosorbent assay we were able to detect substantial amounts of sTRAP in the supernatants of activated T cells. The onset and rate of sTRAP release was found to parallel the expression of TRAP on the cell surface. sTRAP, an 18-kDa protein, is generated by proteolytic processing of full-length TRAP in an intracellular compartment. Starting with methionine 113 of full-length TRAP, sTRAP lacks the transmembrane region and a part of the extracellular domain but contains the entire TNF-alpha homology region and can, therefore, bind to CD40. Like other members of the TNF superfamily (e.g. TNF-alpha, Fas/APO-1 ligand), TRAP thus has the potential to be biologically active not only in a transmembrane form but also as a soluble molecule.
Amino Acid Sequence↗
Modulation of cochlear responses in the guinea pig by low-frequency, phase-shifted maskers following noise trauma.
Low-frequency acoustic biasing using an intensive phase-shifted, low-frequency masker was studied according to its ability to determine disorders of cochlear micromechanics following noise trauma in the guinea pig as animal model. Statistical analyses proved that this technique allowed electrophysiological differentiation of controls versus groups with different degrees of experimentally induced threshold shifts. To substantiate group differences an intensity of at least 70 dB SPL was required for the 52 Hz masker and the difference in relation to the test-tone intensity had to be +/- 10 or +/- 20 dB SPL. The noise-traumatized cochlea could be identified by means of a threshold shift for the 5 microV pseudothreshold, a low modulation span of the compound action potential amplitude (< 25-50 microV frequency dependent), and reduced positive summating potential amplitude with negative non-modulating values within the different measurement phases for 1 and 2 kHz stimulation.
Acoustic Stimulation↗
Dynamic three-dimensional transesophageal echocardiography using a computed tomographic imaging probe--clinical potential and limitation.
Dynamic three-dimensional echocardiography is a new diagnostic tool for spatial visualisation of cardiac anatomy and volumetric assessment. A computer-controlled probe acquires parallel tomographic slices, from which dynamic three-dimensional images of the heart can be reconstructed. Thirty adult patients with valvular heart diseases, congenital heart diseases, intracardiac masses, heart failure and other cardiac lesions, underwent conventional two-dimensional (n = 30), three-dimensional echocardiography (n = 30) and thermodilution (n = 17). The feasibility, usefulness and possibility of simulating a surgical view of intracardiac anatomy and exact volumetry were determined. The two different morphologic images were compared qualitatively. For quantitative analysis volumetry was performed using standard thermodilution technique and dynamic three-dimensional echocardiography. In more than 80% of the patients additional morphologic information was gained and a strong correlation (r = 0.75-0.95) between two volumetry assessments was found. Based on this findings, dynamic three-dimensional echocardiography is an additional and valuable approach in the perioperative and intensive care management in this group of patients.
Adult↗
Leflunomide, a reversible inhibitor of pyrimidine biosynthesis?
Explore the source record for details and available documents.
Cell Division↗
Differential susceptibility of filarial and human erythrocyte glutathione reductase to inhibition by the trivalent organic arsenical melarsen oxide.
The glutathione reductases (GR) from two cattle filariae (Setaria digitata and Onchocerca gutturosa) have been isolated and their properties have been compared to those of human erythrocyte GR. In general, the enzymes appear to be very similar with respect to substrate-specificity for glutathione disulfide and NADPH, molecular mass (97 kDa vs. 98 kDa) and oligomeric organisation (subunit size of 51 kDa vs. 50 kDa). However, studies on the inhibition of the enzymes by the trivalent melaminophenyl arsenical melarsen oxide revealed that the human GR is less susceptible to inhibition by the arsenical than the filarial enzymes. Further, it was found that the mechanism of inactivation differs for the host and filarial enzymes. The human enzyme is inhibited by melarsen oxide in a competitive manner with a Ki of 23.7 microM, whereas the filarial GRs are inhibited in two stages: an immediate partial inactivation followed by a time-dependent stage with saturable pseudo-first-order kinetics. Ki values for the S. digitata and O. gutturosa GRs are 38.3 microM and 4.5 microM, respectively, with maximum second-stage inactivation rates of 1.0 x 10(-4) s-1 and 24.3 x 10(-4) s-1, respectively. These differences between host and parasite enzyme might reflect differences in the primary and secondary structure of the proteins which might be exploitable for the design of new specific macrofilaricidal drugs.
Animals↗
Plasmodium falciparum glutathione reductase exhibits sequence similarities with the human host enzyme in the core structure but differs at the ligand-binding sites.
The homodimeric flavoenzyme glutathione reductase (GR) which catalyzes the reduction of glutathione disulfide is a cornerstone of the malaria parasite antioxidant defense and repair mechanisms. Here we report on the identification of the GR gene from Plasmodium falciparum. A 1.4-kb fragment of the gene was amplified by polymerase chain reaction (PCR). Using this PCR fragment as a probe a full length cDNA clone (2085 bp) was isolated from a P. falciparum gametocyte library. The deduced amino acid sequence of 541 residues shows an overall identity of 35% when compared to the human enzyme. Most amino acids of known function are identical. However, notable differences between human and parasite protein occur in the glutathione-binding pocket (for instance, Glu374 instead of the expected basic residue) and at the intersubunit contact area. These regions are of particular interest since they represent binding sites of known GR inhibitors. Consequently, parasite GR can serve as a target structure for the design of antimalarial drugs.
Amino Acid Sequence↗
Defective B cell development and function in Btk-deficient mice.
Mutations in the Bruton's tyrosine kinase (Btk) gene have been linked to severe early B cell developmental blocks in human X-linked agammaglobulinemia (XLA), and to milder B cell activation deficiencies in murine X-linked immune deficiency (Xid). To elucidate unequivocally potential Btk functions in mice, we generated mutations in embryonic stem cells, which eliminated the ability to encode Btk pleckstrin homology or kinase domains, and assayed their effects by RAG2-deficient blastocyst complementation or introduction into the germline. Both mutations block expression of Btk protein and lead to reduced numbers of mature conventional B cells, severe B1 cell deficiency, serum IgM and IgG3 deficiency, and defective responses in vitro to various B cell activators and in vivo to immunization with thymus-independent type II antigens. These results prove that lack of Btk function results in an Xid phenotype and further suggest a differential requirement for Btk during the early stages of murine versus human B lymphocyte development.
Agammaglobulinaemia Tyrosine Kinase↗
High-level expression of biologically active soluble guanylate cyclase using the baculovirus system is strongly heme-dependent.
Explore the source record for details and available documents.
Animals↗
Metabolism of dynorphin A 1-13 in human blood and plasma.
PURPOSE: A detailed investigation of the metabolic routes and rates of Dyn A1-13 in human blood and plasma was performed. METHODS: Human plasma was incubated at 37 degrees C with dynorphin A 1-13 (Dyn A1-13, 15-20 microM). The generated dynorphin fragments were separated by a new ion-pair chromatographic method and identified by matrix assisted laser desorption mass spectroscopy. The kinetic behavior of parent compound and metabolites was evaluated in the absence and presence of enzyme inhibitors. RESULTS: The major plasma metabolites of Dyn A1-13 were Dyn A1-12, A2-12, A4-12 and A4-8. Further metabolites were Dyn A2-13, A3-13, A3-12, A5-12, A6-12, A7-12, A1-10, A2-10, A2-8 and A3-8. At 37 degrees C, Dyn A1-13 had a half-life of less than one minute in plasma and blood. Plasma half-lives of major metabolites ranged between 0.5 and 4 min. Inter- and intra-individual differences in healthy volunteers were 30% (c.v.). Dyn A1-13 is mainly metabolized by carboxypeptidases to Dyn A1-12 (80%) and by aminopeptidases to Dyn A2-13 (15%). Dyn A1-12 and Dyn A2-13 are predominantly converted into Dyn A2-12 (67% of Dyn A1-13). Subsequent metabolic steps yield Dyn A3-12 (16%), Dyn A4-12 (37%) and Dyn A4-8 (33%). Aminopeptidases generate Dyn A2-12, A3-12, A4-12, A5-12. ACE metabolizes Dyn A1-12 (19%), A2-12 (33%), A3-12 (34%) and A4-12 (46%). Bestatin-sensitive endopeptidases (possibly endopeptidase 24.11) metabolize 30% of Dyn A2-12. Dyn A4-8 is formed via Dyn A4-12 (23% of Dyn A4-12) and Dyn A2-10 (37% of Dyn A2-10). CONCLUSIONS: The combination of enzyme inhibition experiments and noncompartmental kinetic analysis proved to be a powerful tool for the detailed evaluation of the metabolic fate of Dyn A1-13 in human blood and plasma.
Adult↗
The role of G-protein beta gamma subunits in signal transduction.
Explore the source record for details and available documents.
Adenylyl Cyclases↗
Structural analysis of the p62 complex, an assembly of O-linked glycoproteins that localizes near the central gated channel of the nuclear pore complex.
The p62 complex is an oligomeric assembly of O-linked glycoproteins of the nuclear pore complex that interacts with cytosolic transport factors and is part of the machinery for nuclear protein import. In this study we have purified the p62 complex from rat liver nuclear envelopes and analyzed its structure and composition. The p62 complex consists of four distinct polypeptides (p62, p58, p54, and p45) and has a mass of approximately 234 kDa, calculated from its hydrodynamic properties and supported by chemical cross-linking and scanning transmission electron microscopy. These data suggest that the p62 complex contains one copy of each constituent polypeptide. Analysis of preparations of the p62 complex by electron microscopy using rotary metal shadowing and negative staining revealed donut-shaped particles with a diameter of approximately 15 nm. Immunogold electron microscopy of isolated rat liver nuclear envelopes demonstrated that p62 occurs on both the nucleoplasmic and cytoplasmic sides of the pore complex near the central gated channel involved in active transport of proteins and RNAs. The properties and localization of the p62 complex suggest that it may be involved in binding transport ligands near the center of the nuclear pore complex and in subsequently transferring them to the gated transport channel.
Animals↗
DNA-based mutation analysis of Bruton's tyrosine kinase gene in patients with X-linked agammaglobulinaemia.
The identification of the BTK (Bruton's tyrosine kinase) gene defective in human immunoglobulin deficiency X-linked agammaglobulinaemia (XLA) and characterisation of BTK exon-intron boundaries has now allowed the analysis of mutations and polymorphisms at the level of genomic DNA. Using Southern blot analysis and the polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) assay, amplifying all 19 exons and the putative promoter region with a single annealling temperature, mutations have been identified in 19 out of 24 unrelated patients diagnosed as having XLA. Apart from a large deletion involving exon 19, nine missense (F25S, R288W, 1370M, M509V, R525P, N526K, R562W, A582V and G594R), two nonsense (E277X and R525X), five frameshift and two splice site mutations have been found affecting most coding exons and all major enzyme domains. No mutations or polymorphisms were detected in the putative promoter region. A single nucleotide deletion located in the last exon, resulting in a truncation of the eight C-terminal residues of Btk and a typical XLA phenotype, indicates structural and/or functional importance of Btk helix I in the catalytic domain. Although allelic heterogeneity at the BTK locus may partly explain clinical variability in families with XLA, compensatory and redundant mechanisms involved in B-cell development must play a role in the phenotypic diversity of the disease.
Adolescent↗
Transcriptional regulation of intercellular adhesion molecule-1: PMA-induction is mediated by NF kappa B.
The surface glycoprotein intercellular adhesion molecule-1 (ICAM-1) mediates important immunologic cell interactions during cutaneous inflammatory processes by binding to the leukocyte integrin lymphocyte function-associated antigen-1. The expression of ICAM-1 is induced in epidermal keratinocytes by certain pro-inflammatory stimuli, and this modulation is transcriptionally regulated. To identify the molecular mechanisms involved in the regulation of ICAM-1 gene expression, we have previously cloned the transcriptional regulatory region of the human ICAM-1-gene and have characterized a functional promoter. Here we have used the phorbol ester phorbol-12-myristate-13-acetate (PMA) to further evaluate the transcriptional mechanisms of ICAM-1 gene induction in A431 cells. Exposure to PMA induced ICAM-1 both at the mRNA and cell surface level. Promoter activity and PMA-enhanced effects were assessed by transiently transfecting A431 cells with chloramphenicol acetyl transferase reporter gene constructs containing a series of sequential ICAM-1 5' deletions. Constructs containing ICAM-1 5' fragments from -1162/+1 (relative to the transcription start site) to -277/+1 displayed a threefold increase in promoter activity when cells were stimulated with PMA. Inducibility dropped below 1.5-fold in chloramphenicol acetyl transferase construct -182/+1. Using electrophoretic mobility shift assays, a PMA-inducible binding site was identified for an NF kappa B-like complex within positions -186/-177. A -199/-170 fragment containing this NF kappa B-like element conferred PMA responsiveness when cloned into a thymidine kinase-driven chloramphenicol acetyl transferase vector, indicating that the region containing this NF kappa B-like element is not only necessary but also sufficient for PMA induction of ICAM-1.
Base Sequence↗