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Biomedical subjects

L Tang

Publications and source records attributed to L Tang.

At least 37 records · Page 2Linked to original sources
PubMed2003

Structure and mechanism of a bacterial haloalcohol dehalogenase: a new variation of the short-chain dehydrogenase/reductase fold without an NAD(P)H binding site.

Haloalcohol dehalogenases are bacterial enzymes that catalyze the cofactor-independent dehalogenation of vicinal haloalcohols such as the genotoxic environmental pollutant 1,3-dichloro-2-propanol, thereby producing an epoxide, a chloride ion and a proton. Here we present X-ray structures of the haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1, and complexes of the enzyme with an epoxide product and chloride ion, and with a bound haloalcohol substrate mimic. These structures support a catalytic mechanism in which Tyr145 of a Ser-Tyr-Arg catalytic triad deprotonates the haloalcohol hydroxyl function to generate an intramolecular nucleophile that substitutes the vicinal halogen. Haloalcohol dehalogenases are related to the widespread family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDR family), which use a similar Ser-Tyr-Lys/Arg catalytic triad to catalyze reductive or oxidative conversions of various secondary alcohols and ketones. Our results reveal the first structural details of an SDR-related enzyme that catalyzes a substitutive dehalogenation reaction rather than a redox reaction, in which a halide-binding site is found at the location of the NAD(P)H binding site. Structure-based sequence analysis reveals that the various haloalcohol dehalogenases have likely originated from at least two different NAD-binding SDR precursors.

Amino Acid Sequence↗
PubMed2003

Measurements of GnE/GnM from the 2H(e-->,en-->)1H Reaction to Q2=1.45 (GeV/c)2.

We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G(n)(E)/G(n)(M), obtained via recoil polarimetry from the quasielastic 2H(e-->,e(')n-->)1H reaction at Q2 values of 0.45, 1.13, and 1.45 (GeV/c)(2) with relative statistical uncertainties of 7.6% and 8.4% at the two higher Q2 points, which points have never been achieved in polarization measurements.

Journal Article↗
PubMed2003

High resolution spectroscopy of the 12Lambda B hypernucleus produced by the (e,e'K+) reaction.

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.

Journal Article↗
PubMed2003

Human brain wave activity during exposure to radiofrequency field emissions from mobile phones.

The aim of this study was to determine whether there is an effect of mobile phone electromagnetic field emissions on the human electroencephalograph (EEG). EEG recordings from ten awake subjects were taken during exposure to radiofrequency (RF) emissions from a mobile phone positioned behind the head. Two experimental trials were conducted. In the first trial, RF exposures were generated by a GSM mobile phone with the speaker disabled and configured to transmit at full-radiated power. During the second trial, exposures were generated by a non-modified GSM mobile phone in active standby mode. For each trial, subjects were exposed in five minute intervals to a randomized, interrupted sequence of five active and five sham exposures. The experiment was conducted under single-blind conditions. The average EEG band power in active exposure recordings was compared to corresponding sham recordings. Statistical tests indicated significant difference in the full-power mode trial within the EEG alpha (8-13 Hz) and beta (13-32 Hz) bands. A subsequent statistical analysis of median spectral power in discrete EEG rhythms revealed significant differences in 7 of the 32 distinct frequencies overall. In conclusion, the results of this study lend support to EEG effects from mobile phones activated in talk-mode.

Adolescent↗
PubMed2003

In vitro hemocompatibility studies of drug-loaded poly-(L-lactic acid) fibers.

Our objective was to evaluate the hemocompatibility of biodegradable stent fibers, employing a closed-loop circulation system filled with human blood. We also investigated the effects of the anti-inflammatory and anti-proliferative drugs curcumin and paclitaxel, incorporated into stent fibers. Fresh whole blood was circulated in four parallel closed-loop systems: the empty tube circuit (control) and tubes containing either a PLLA fiber coil (PLLA), a curcumin-loaded PLLA coil (C-PLLA) or a paclitaxel-loaded PLLA coil (P-PLLA). The influence of PLLA fiber, alone or loaded with drug incorporated during melt-extrusion, on leukocyte and platelet adhesion and activation was determined by flow cytometry. The effects of blood flow and fiber properties on cell deposition were assessed by scanning electron microscopy (SEM). The flow cytometry results clearly demonstrated that PLLA triggers blood cell activation at the site of deployment, as shown by increases in CD11b, CD62P and leukocyte-platelet aggregates, compared to controls. Curcumin and paclitaxel treatments both significantly reduced leukocyte and platelet activation and adhesion to PLLA fibers, as shown by flow cytometry and SEM. Activated leukocytes and platelets revealed significantly lower CD11b and CD62P receptor binding for C-PLLA compared with PLLA alone, and slightly lower for P-PLLA. Reductions in platelet-leukocyte aggregates were observed as well. In addition, there was less leukocyte and platelet adhesion to C-PLLA, compared with PLLA fiber controls, as shown by SEM. A continuous linear thrombus, composed of platelets, leukocytes, red blood cells and fibrin was occasionally detected along the line of tangency between the coil and the tube wall. Flow separation and eddying, proximal and distal to the line of tangency of coil and tube, is thought to contribute to this deposit. Curcumin was more effective than paclitaxel in reducing leukocyte and platelet activation and adhesion to PLLA stent fibers in this setting. However there was evidence of paclitaxel degeneration during melt extrusion that may have inhibited its effectiveness. Incorporation of the anti-inflammatory and anti-proliferative drug curcumin into bioresorbable stent fibers is proposed to prevent thrombosis and in-stent restenosis.

Anti-Inflammatory Agents↗
PubMed2003

The inhibitory effect of VitD3 on proliferation of keratinocyte cell line HACAT is mediated by down-regulation of CXCR2 expression.

Psoriasis is a disease characterized by inflammation and increased population of hyperproliferative keratinocytes. It is well known that chemokines and chemokine receptors, such as interleukin-8 and its receptors (CXCR1 and CXCR2), play important roles in the pathogenesis of psoriasis. So far, examination of CXCR2 expression in psoriatic lesional keratinocytes by FACS calibur has not been reported and whether VitD3 inhibits psoriatic lesional keratinocyte proliferation through down-regulation of CXCR2 expression has not been elucidated. In the present study, CXCR2 expression in psoriatic lesional keratinocytes and HACAT treated with VitD3 was detected by flow cytometry. The proliferative capacity of HACAT treated with VitD3 was assayed by MTT assay. The results showed that CXCR2 expression in psoriatic lesional keratinocytes was higher than that in normal human keratinocytes. At the correct concentration VitD3 could inhibit human keratinocyte proliferation and down-regulate CXCR2 expression in HACAT. The data demonstrate that the inhibitory effect of VitD3 on keratinocyte proliferation might be mediated by down-regulation of CXCR2 expression.

Administration, Topical↗
PubMed2003

Comparison of the expression of Bacillus thuringiensis full-length and N-terminally truncated vip3A gene in Escherichia coli.

AIMS: Studies were performed to demonstrate the function of the putative signal peptide of Vip3A proteins in Escherichia coli. METHODS AND RESULTS: The full-length vip3A-S184 gene was isolated from a soil-isolated Bacillus thuringiensis, and the vip3AdeltaN was constructed by deleting 81 nucleotides at the 5'-terminus of vip3A-S184. Both were transformed and expressed in E. coli. About 19.2% of Vip3A-S184 proteins secreted soluble proteins and others formed inclusion bodies in the periplasmic space. In contrast, the Vip3AdeltaN was insoluble and formed inclusion bodies in the cytoplasm. Bioassay indicated that Vip3A-S184 showed different toxicity against Spodoptera exigua, Helicoverpa armigera and S. litura, but Vip3AdeltaN showed no toxicity to either of them because of the deletion of the first 27 amino acids at the N-terminus. CONCLUSIONS: The results suggest that the deleted N-terminal sequences were essential for the secretion of Vip3A-S184 protein in E. coli and might be required for toxicity. SIGNIFICANCE AND IMPACT OF THE STUDY: The function of the putative signal peptide of Vip3A protein in E. coli was investigated. These would be helpful to make clear the unknown secretion pathway of Vip3A protein in B. thuringiensis and determine the receptor-binding domain or toxic fragment of Vip3A-S184 protein.

Amino Acid Sequence↗
PubMed2003

Identification of bulb from Fritillaria cirrhosa by PCR with specific primers.

Bulb of Fritillaria cirrhosa is an important traditional Chinese herbal medicine. According to the Chinese Pharmacopoeia (1995), it is commonly used as an antitussive and expectorant. Many young bulbs from species of Fritillaria are similar to those of F. cirrhosa, but they are different in price and quality. Therefore, there are many young bulbs from species of Fritillaria that could fake those of F. cirrhosa on the commercial market. The coding region of 5S-rRNA is highly conserved in higher eukaryotes. The 5S-rRNA spacer region sequences of F. thunbergii, F. pallidiflora, F. ussuriensi, F. delavayi, F.cirrhosa, F. anhuiensis, F. puqiensis were cloned by PCR with a pair of primers located within the conserved coding region. Based on sequences analyses of the 5S-rRNA spacer region from the 7 species, a specific sequence was found in F. cirrhosa. A pair of specific primers was designed for differentiating the bulbs of F. cirrhosa from each other by PCR. This result indicated that the method is rapid, more accurate and applicable in identification of the bulbs of F. cirrhosa at the DNA level.

Base Sequence↗
PubMed2002

Sigma-nucleus potential in A=28.

We have studied the (pi(-),K+) reaction on a silicon target to investigate the sigma-nucleus potential. The inclusive spectrum was measured at a beam momentum of 1.2 GeV/c with an energy resolution of 3.3 MeV (FWHM) by employing the superconducting kaon spectrometer system. The spectrum was compared with theoretical calculations within the framework of the distorted-wave impulse approximation, which demonstrates that a strongly repulsive sigma-nucleus potential with a nonzero size of the imaginary part reproduces the observed spectrum.

Journal Article↗
PubMed2002

Hypernuclear fine structure in (9)(lambda)Be.

With a germanium detector array (Hyperball), we observed two gamma-ray peaks corresponding to the two transitions (5/2(+)-->1/2(+) and 3/2(+)-->1/2(+)) in the (9)(Lambda)Be hypernucleus which was produced by the 9Be(K-,pi(-)) reaction. The energies of the gamma rays are 3029 +/- 2 +/- 1 keV and 3060 +/- 2 +/- 1 keV. The energy difference was measured to be 31.4(+2.5)(-3.6) keV, which indicates a very small Lambda-spin-dependent spin-orbit force between a Lambda and a nucleon. This is the smallest level splitting by far ever measured in a hypernucleus.

Journal Article↗
PubMed2001

Identification of two novel human dynein light chain genes, DNLC2A and DNLC2B, and their expression changes in hepatocellular carcinoma tissues from 68 Chinese patients.

Two full-length cDNAs, DNLC2A and DNLC2B, were cloned and characterized. Their open reading frames respectively encode 96 amino acids which are most closely homologous to roadblock/LC7, one member of an ancient dynein light chain protein family, conserved in nematode, fruit fly, mouse and rat. The DNLC2A was expressed in 12 of 16 human tissues examined, with especially strong expression in heart, liver and brain, whereas there was weak expression in lung, prostate, testis, small intestine and colon. The expression of DNLC2B was generally high compared with that of DNLC2A except in liver. Northern blotting and/or semi-quantitative RT-PCR analysis examined the expression changes of DNLC2A and DNLC2B in 68 hepatocellular carcinoma tissue samples. It was revealed that DNLC2A was up-regulated (45 out of the 68 cases) while DNLC2B was down-regulated (44 out of 68 cases), compared with their adjacent tumor-free liver tissues. Interestingly, among the total 68 liver cancer samples tested, DNLC2A was up-regulated while DNLC2B was down-regulated in 28 cases; DNLC2A was up-regulated while no obvious change was observed for DNLC2B in 10 cases; no obvious change was observed for DNLC2A while DNLC2B was down-regulated in 14 cases. Although the underlying mechanism is not clear to date, the apparent up-regulation of DNLC2A and down-regulation of DNLC2B suggest that these genes might be involved in tumor progression. On the other hand, the different expression changes of the two homologous genes indicate that hepatocellular carcinomas are caused by different pathological mechanisms. In addition, DNLC2A was assigned to human chromosome 20q12-q13.11 near the marker D20S106 by radiation hybrid mapping.

Adult↗
PubMed2001

Characterization of virus-like particles assembled in a recombinant baculovirus system expressing the capsid protein of a fish nodavirus.

Betanodaviruses are causative agents of neurological disorders in several species of fish. We cloned and sequenced the RNA2 segment of two grouper viruses isolated from Epinephelus malabaricus (malabaricus grouper nervous necrosis virus, MGNNV) and Epinephelus lanceolatus (dragon grouper nervous necrosis virus, DGNNV). The sequences of the two RNAs were 99% identical and comparison with previously sequenced RNA2 segments of fish nodaviruses striped jack nervous necrosis virus, Atlantic halibut virus, sea bass encephalitis virus, and greasy grouper nervous necrosis virus (GGNNV) revealed that MGNNV and DGNNV were most closely related to GGNNV. No correlation of sequence with geographical habitat was detected. The MGNNV coat protein, the gene product of RNA2, was expressed in Sf21 cells with a recombinant baculovirus system and virus-like particles (VLPs) spontaneously formed. Two types of VLPs were observed: a slower sedimenting particle was RNase-sensitive and stain-permeable, while the faster sedimenting particle survived RNase treatment and was not stain-permeable. An image reconstruction of the latter, obtained with electron cryomicroscopy data, revealed a morphology consistent with T = 3 quasi-symmetry but with features significantly different from insect nodavirus structures at the same resolution. This assembly system allows the first biophysical comparisons of fish and insect nodavirus structure, assembly, and stability.

Amino Acid Sequence↗
PubMed2001

Insights into the signal transduction mechanism of RmFixL provided by carbon monoxide recombination kinetics.

This report presents evidence for interdomain steps of the ligand-coupled signal transduction mechanism of the oxygen receptor from Rhizobium meliloti, RmFixL. Photolysis of the CO adducts of heme domain (RmFixLN) and heme kinase (RmFixL*) proteins allowed tracking of second-order heme CO recombination reactions by transient absorbance. Whereas CO rebinding to RmFixLN is characterized by a single kinetic phase, rebinding to RmFixL* is characterized by two kinetic phases. Evidence indicates that CO rebinds to two interconvertible deoxyRmFixL* conformers that are produced sequentially after photolysis. Since the second conformer is only observed when the kinase domain is present, its production is concluded to be an interdomain signal transmission event that is coupled to heme ligand release. Because receptor clustering is a recurring theme in signal transduction mechanisms, the dependence of molecular weight upon heme ligation was investigated at equilibrium. Gel permeation chromatography and native gel electrophoresis showed that the molecular weight distribution for both RmFixLN and RmFixL* depends on heme ligation. At equilibrium, oxyRmFixLN and oxyRmFixL* exist as monomers and dimers, respectively. Their deoxy analogues, metRmFixLN and metRmFixL*, exist as dimers and as a mixture of tetramers and 9-mers, respectively. Assembly of these oligomers is reversible. The physiological relevance of these ligand-coupled assemblies and the kinetic factors controlling CO recombination are discussed.

Bacterial Proteins↗
PubMed2001

Longitudinal electroproduction of charged pions from (1)H, (2)H, and (3)He.

Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in (3)He at W = 1.60 GeV. The W = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.

Journal Article↗
PubMed2001

Production of (4)(double Lambda)H hypernuclei.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

Journal Article↗
PubMed2001

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

Journal Article↗
PubMed2001

Molecular basis of biomaterial-mediated foreign body reactions.

Despite being inert and nontoxic, implanted biomaterials often trigger adverse foreign body reactions such as inflammation, fibrosis, infection, and thrombosis. With regard to the inflammatory responses to biomaterial implants, it was previously found that a crucial precedent event was the spontaneous adsorption and denaturation of fibrinogen on implant surfaces. It was further found that interactions between the phagocyte integrin Mac-1 (CD11b/CD18) and one short sequence within the fibrinogen D domain (gamma 190-202; P1) at least partially explained phagocyte accumulation on implant surfaces. However, the reason that adsorbed fibrinogen is proinflammatory--while soluble fibrinogen clearly is not--remained obscure. In this study, therefore, the question of how fibrinogen is converted to a proinflammatory state when adsorbed to biomaterial surfaces is investigated. In soluble fibrinogen, the 13 amino acid P1 sequence was found to be hidden. However, the adsorption and denaturation of fibrinogen on the surfaces of commonly used biomaterials lead to the exposure of P1 and a second neo-epitope, gamma 377-395 (P2), which also interacts with Mac-1 and is similarly occult in the soluble protein. The extent of biomaterial-mediated P1 and P2 exposure appears directly related to the severity of inflammatory responses to a test panel of biomaterials. Finally, thrombin-mediated conversion of fibrinogen to fibrin also exposes both P1 and P2 epitopes. These observations may help explain both the inflammation caused by many types of implanted biomaterials and that which occurs naturally following thrombotic events. (Blood. 2001;98:1231-1238)

Adsorption↗