Search PubMed⌕ Search

Biomedical subjects

J Tang

Publications and source records attributed to J Tang.

At least 91 records · Page 5Linked to original sources
PubMed2001

[Transmission properties of Faraday anomalous dispersion optical filter at 532 nm].

In this paper the properties of an excited-state potassium Faraday anomalous dispersion optical filter in potassium vapor with a pump wavelength of 769.90 nm (i.e. 4S1/2-->4P1/2 transition) and a signal wavelength of 532 nm (i.e. 4P1/2-->8S1/2 transition) are calculated and discussed. The filter's transmissions versus the laser pump power and the external magnetic-field are obtained. The theoretical results show the transmission characteristics of the filter are relatively insensitive to the laser pump power and magnetic strength. The laser pump powers require range from 0.8 to 6 mW.cm-2. Our model predicts a peak transmission of 50% and an equivalent band-width of 4 GHz for the filter operating on the 4P1/2<--8S1/2 transition in potassium. The optical filter at 532 nm presented in this paper may be used to detect the practical and important frequency-doubled Nd:YAG laser.

English Abstract↗
PubMed2000

Mechanisms of [Ca2+]i elevation by H2O2 in islets of rats.

Activity of reactive oxygen species is elevated in diabetes mellitus and has been implicated in the destruction of cellular components. The toxic effect of reactive oxygen species was investigated by testing the effect of H2O2 on [Ca2+]i in isolated islets of Langehans. H2O2 increased [Ca2+]i in a dose-dependent manner, which was irreversible at high concentrations. The maximum effect of H2O2 on [Ca2+]i was larger than those of KCl, glucose, ATP, carbachol and endothelin-1. The effect of H2O2 was only partially attenuated by removal of external Ca2+ and by the in-organic Ca2+ channel blocker nickel, but was not blocked by voltage-dependent or -independent Ca2+ channel blockers nimodipine, nicardipine, SK&F 96365, econazole and lanthanum. H2O2, disrupted [Ca2+]i homeostasis in islets by affecting both release and influx of Ca2+ and causing dysfunction of Ca2+ clearance systems and may contribute to the pathological process of diabetes.

Animals↗
PubMed2000

Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode.

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.

Carbon↗
PubMed2000

Association of mammalian trp4 and phospholipase C isozymes with a PDZ domain-containing protein, NHERF.

Mammalian homologues of Drosophila Trp have been implicated to form channels that are activated following the depletion of Ca(2+) from internal stores. Recent studies indicate that actin redistribution is required for the activation of these channels. Here we show that murine Trp4 and Trp5, as well as phospholipase C beta1 and beta2 interact with the first PDZ domain of NHERF, regulatory factor of the Na(+)/H(+) exchanger. We demonstrated the association of Trp4 and phospholipase C-beta1 with NHERF in vivo in an HEK293 cell line expressing Trp4 and in adult mouse brain by immuno-coprecipitation. NHERF is a two PDZ domain-containing protein that associates with the actin cytoskeleton via interactions with members of ezrin/radixin/moesin family. Thus, store-operated channels involving Trp4 and Trp5 can form signaling complexes with phospholipase C isozymes via interactions with NHERF and thereby linking the lipase and the channels to the actin cytoskeleton. The interaction with the PDZ protein may constitute an important mechanism for distribution and regulation of store-operated channels.

Amino Acid Sequence↗
PubMed2000

Dynamics and folding of single two-stranded coiled-coil peptides studied by fluorescent energy transfer confocal microscopy.

We report single-molecule measurements on the folding and unfolding conformational equilibrium distributions and dynamics of a disulfide crosslinked version of the two-stranded coiled coil from GCN4. The peptide has a fluorescent donor and acceptor at the N termini of its two chains and a Cys disulfide near its C terminus. Thus, folding brings the two N termini of the two chains close together, resulting in an enhancement of fluorescent resonant energy transfer. End-to-end distance distributions have thus been characterized under conditions where the peptide is nearly fully folded (0 M urea), unfolded (7.4 M urea), and in dynamic exchange between folded and unfolded states (3.0 M urea). The distributions have been compared for the peptide freely diffusing in solution and deposited onto aminopropyl silanized glass. As the urea concentration is increased, the mean end-to-end distance shifts to longer distances both in free solution and on the modified surface. The widths of these distributions indicate that the molecules are undergoing millisecond conformational fluctuations. Under all three conditions, these fluctuations gave nonexponential correlations on 1- to 100-ms time scale. A component of the correlation decay that was sensitive to the concentration of urea corresponded to that measured by bulk relaxation kinetics. The trajectories provided effective intramolecular diffusion coefficients as a function of the end-to-end distances for the folded and unfolded states. Single-molecule folding studies provide information concerning the distributions of conformational states in the folded, unfolded, and dynamically interconverting states.

Amino Acid Sequence↗
PubMed2000

Insights into the molecular basis of leukocyte tethering and rolling revealed by structures of P- and E-selectin bound to SLe(X) and PSGL-1.

P-, E- and L-selectin constitute a family of cell adhesion receptors that mediate the initial tethering and rolling of leukocytes on inflamed endothelium as a prelude to their firm attachment and extravasation into tissues. The selectins bind weakly to sialyl Lewisx (SLe(X))-like glycans, but with high-affinity to specific glycoprotein counterreceptors, including PSGL-1. Here, we report crystal structures of human P- and E-selectin constructs containing the lectin and EGF (LE) domains co-complexed with SLe(X). We also present the crystal structure of P-selectin LE co-complexed with the N-terminal domain of human PSGL-1 modified by both tyrosine sulfation and SLe(X). These structures reveal differences in how E- and P-selectin bind SLe(X) and the molecular basis of the high-affinity interaction between P-selectin and PSGL-1.

Amino Acid Sequence↗
PubMed2000

Proteolytic activation of recombinant pro-memapsin 2 (pro-beta-secretase) studied with new fluorogenic substrates.

Memapsin 2 (beta-secretase), a membrane-anchored aspartic protease, is involved in the cleavage of beta-amyloid precursor protein to form beta-amyloid peptide. The primary structure of memapsin 2 suggests that it is synthesized in vivo as pro-memapsin 2 and converted to memapsin 2 by an activating protease [Lin et al. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 1456-1460]. To simulate this activation mechanism and to produce stable mature memapsin 2 for kinetic/specificity studies, we have investigated the activation of recombinant pro-memapsin 2 by several proteases with trypsin-like specificity. Clostripain, kallikrein, and trypsin increased the activity of pro-memapsin 2. Clostripain activation was accompanied by the cleavage of the pro region to form mainly two activation products, Leu(30p)- and Gly(45p)-memapsin 2. Another activation product, Leu(28p)-memapsin 2, was also purified. Kinetics of the activated memapsin 2 were compared with pro-memapsin 2 using two new fluorogenic substrates, Arg-Glu(5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (EDANS))-Glu-Val-Asn-Leu-Asp-Ala-Glu-Phe-Lys(4-(4-dimethylaminophe nyl azo)benzoic acid (DABCYL))-Arg and (7-methoxycoumarin-4-yl)acetyl (MCA))-Ser-Glu-Val-Asn-Leu-Asp-Ala-Glu-Phe-Lys(2,4-dinitrophenyl (DNP)). These results establish that the activity of pro-memapsin 2 stems from a part-time and reversible uncovering of its active site by its pro region. Proteolytic removal of part of the pro-peptide at Leu(28p) or Gly(45p), which diminishes the affinity of the shortened pro-peptide to the active site, results in activated memapsin 2. These results also suggest that Glu(33p)-memapsin 2 observed in the cells expressing this enzyme [Vassar et al. (1999) Science 286, 735-741; Yan et al. (1999) Nature 402, 533-537] is an active intermediate of in vivo activation, or that the peptide Glu(33p)-Arg(44p) may serve a regulatory role.

Amino Acid Sequence↗
PubMed2000

Structure of the protease domain of memapsin 2 (beta-secretase) complexed with inhibitor.

Memapsin 2 (beta-secretase) is a membrane-associated aspartic protease involved in the production of beta-amyloid peptide in Alzheimer's disease and is a major target for drug design. We determined the crystal structure of the protease domain of human memapsin 2 complexed to an eight-residue inhibitor at 1.9 angstrom resolution. The active site of memapsin 2 is more open and less hydrophobic than that of other human aspartic proteases. The subsite locations from S4 to S2' are well defined. A kink of the inhibitor chain at P2' and the change of chain direction of P3' and P4' may be mimicked to provide inhibitor selectivity.

Amyloid Precursor Protein Secretases↗
PubMed2000

Compressibility and polygonization of single-walled carbon nanotubes under hydrostatic pressure

Single-walled carbon nanotubes show linear elasticity under hydrostatic pressure up to 1.5 GPa at room temperature. The volume compressibility, measured by in situ synchrotron x-ray diffraction, has been determined to be 0.024 GPa (-1). Theoretical calculations suggest that single-walled carbon nanotubes are polygonized when they form bundles of hexagonal close-packed structure and the intertubular gap is smaller than the equilibrium spacing of graphite (002) (d = 3.35 A). It has also been determined that the deformation of the trigonal nanotube lattice under hydrostatic pressure is reversible up to 4 GPa, beyond which the nanotube lattice is destroyed.

Journal Article↗
PubMed2000

Study on colloidal Au-enhanced DNA sensing by quartz crystal microbalance.

Colloidal Au is reported for enhancement the immobilization capacity and ultimately detection limit of DNA using quartz crystal microbalance (QCM). Immobilization of approximately 12 nm-diameter colloidal Au on to an Au-coated QCM resulted in an easier attachment of oligonucleotide, with a mercaptohexyl group at the 5'-phosphate end and an increased capacity for nucleic acid detection. DNA immobilization and hybridization was monitored from QCM frequency changes. Hybridization was induced by exposure of the DNA-containing films to complementary DNA in solution. A much higher sensitivity was obtained for the analyte. The Au nanoparticle films on the Au plate provide a novel means for the fabrication of DNA sensor.

Animals↗
PubMed2000

Requirement of sphingolipid alpha-hydroxylation for fungicidal action of syringomycin E.

Syringomycin E is an antifungal cyclic lipodepsinonapeptide produced by Pseudomonas syringae pv. syringae. To understand the mechanism of action of syringomycin E, a novel resistant Saccharomyces cerevisiae strain, BW7, was isolated and characterized. Lipid analyses revealed that BW7 contained only the hydrophobic subspecies of sphingolipids that are normally minor components in wild type strains. This aberrant sphingolipid composition was the result of lack of alpha-hydroxylation of the amide-linked very long chain fatty acids, suggesting a defective sphingolipid alpha-hydroxylase encoded by the FAH1 gene. A yeast strain that lacks the FAH1 gene was resistant to syringomycin E, and failed to complement BW7. These results demonstrate that BW7 carries a mutation in the FAH1 gene, and that the lack of alpha-hydroxylated very long chain fatty acids in yeast sphingolipids confers resistance to syringomycin E.

Antifungal Agents↗
PubMed2000

Charged residues dominate a unique interlocking topography in the heterodimeric cytokine interleukin-12.

Human interleukin-12 (IL-12, p70) is an early pro-inflammatory cytokine, comprising two disulfide-linked subunits, p35 and p40. We solved the crystal structures of monomeric human p40 at 2.5 A and the human p70 complex at 2.8 A resolution, which reveals that IL-12 is similar to class 1 cytokine-receptor complexes. They also include the first description of an N-terminal immunoglobulin-like domain, found on the p40 subunit. Several charged residues from p35 and p40 intercalate to form a unique interlocking topography, shown by mutagenesis to be critical for p70 formation. A central arginine residue from p35 projects into a deep pocket on p40, which may be an ideal target for a small molecule antagonist of IL-12 formation.

Arginine↗
PubMed2000

Enzymic characteristics of secreted aspartic proteases of Candida albicans.

Candida yeasts are rarely infectious, but frequently cause life-threatening systemic infections in patients immunocompromised by AIDS or by immunosuppressive therapeutics. The secreted aspartic proteases (Saps) are known virulence factors of pernicious Candida species. The most virulent, Candida albicans, possesses at least nine SAP genes, some of which are specifically expressed from cells with morphologies associated with virulence. Only one of these proteases, Sap2, has been previously purified from yeast in sufficient quantities for enzymic studies. The other enzymes are present in low amounts in yeast culture and are difficult to purify. As a consequence, enzyme properties, including the substrate specificities, of all Saps are poorly studied. Therefore, four Saps that are known to be expressed in C. albicans, Sap1, Sap2, Sap3 and Sap6, were produced in Escherichia coli as recombinant zymogens and purified in large quantities. These proenzymes were autoactivated and purified as active proteases. The enzymic properties including the substrate specificities at the P(1) and P(1)' sites were determined using a competitive hydrolysis method employing synthetic substrate mixtures. All four Saps cleave peptide bonds between larger hydrophobic amino acids, but these somewhat broad specificities differ in detail among the four enzymes at both sites. At the P(1) site, Sap1, Sap2 and Sap6 prefer Phe while Sap3 prefers Leu. Positively charged amino acids are also accommodated, especially by Sap2 and Sap3. The specificities at P(1)' are broader than at P(1) for all four enzymes. Sap6 prefers Ala, whereas other Saps prefer Tyr. Acidic side chains are also accommodated at this site. Analysis of substrates with a hydrophobic amino acid in P(1)' reveals that all the Saps possess a unique preference for Ala at this site. The observed differences of residue preferences among Saps may be utilized for the design of specific substrates and inhibitors.

Aspartic Acid Endopeptidases↗
PubMed2000

Protein-arginine methyltransferase I, the predominant protein-arginine methyltransferase in cells, interacts with and is regulated by interleukin enhancer-binding factor 3.

Arginine methylation is a common post-translation modification found in many proteins. Protein-arginine methyltransferase I (PRMT1) contributes >90% of type I protein-arginine methyltransferase activity in cells and tissues. To expand our knowledge on the regulation and role of PRMT1 in cells, we used the yeast two-hybrid system to identify proteins that interact with PRMT1. One of the interacting proteins we cloned is interleukin enhancer-binding factor 3 (ILF3), also known as M phase phosphoprotein 4. ILF3 is closely related to nuclear factor 90 (NF90). Using an immunofluorescence analysis, we determined that ILF3 and PRMT1 co-localize in the nucleus. Moreover, PRMT1 and ILF3 co-precipitate in immunoprecipitation assays and can be isolated together in "pull-down" experiments using recombinant fusion proteins. ILF3 is a robust substrate for methylation by PRMT1 and can modulate PRMT1 activity in in vitro methylation assays. Deletion studies demonstrated that the COOH-terminal region of ILF3, which is rich in arginine, glycine, and serine, is responsible for the strong interaction between PRMT1 and ILF3 and is the site of ILF3 methylation by PRMT1. Although ILF3 and NF90 are highly similar, they differ in their carboxyl-terminal regions. Because of this difference, NF90 does not interact with PRMT1, is a much poorer substrate than ILF3 for PRMT1-dependent methylation, and does not modulate PRMT1 enzyme activity.

Amino Acid Sequence↗
PubMed2000

Isolation and preparative purification of microcystin variants.

Preparative reversed-phase liquid chromatography was successfully used to purify two microcystins (microcystin LR and microcystin LA) from a cyanobacterial process waste. The separation protocol involved extraction of lyophilized cells by methanol, isolation and concentration by solid-phase extraction, and purification by reversed-phase HPLC. Milligram-level loading of microcystins was obtained on a solid-phase extraction cartridge packed with 0.5 g of C18 stationary phase. The separations were first carried out on an analytical column and then scaled-up to a preparative column. The microcystins were quantified by HPLC and enzyme-linked immunosorbent assay. A method to remove microcystins rapidly and economically from the cyanobacterial process waste is also described.

Bacterial Toxins↗
PubMed2000

Structural diversity of self-cleaving ribozymes.

In vitro selection was used to isolate Mg(2+)-dependent self-cleaving ribozymes from random sequence. Characterization of representative clones revealed the emergence of at least 12 classes of ribozymes that adopt distinct secondary structure motifs. Only one class corresponds to a previously known structural motif, that of the naturally occurring hammerhead ribozyme. Each ribozyme promotes self-cleavage via an internal phosphoester transfer reaction involving the adjacent 2'-hydroxyl group with a chemical rate enhancement of between 10(3)- and 10(6)-fold greater than the corresponding uncatalyzed rate. These findings indicate that RNA can form a multitude of secondary and tertiary structures that promote cleavage by internal phosphoester transfer. Upon further in vitro selection, a class I ribozyme that adopts an "X motif" structure dominates over all other ribozymes in the population. Thus, self-cleaving RNAs isolated by in vitro selection from random-sequence populations can rival the catalytic efficiency of natural ribozymes.

Amino Acid Motifs↗