Search PubMed⌕ Search

Biomedical subjects

J Tang

Publications and source records attributed to J Tang.

At least 181 records · Page 10Linked to original sources
PubMed1999

Crystal structure of streptokinase beta-domain.

Streptokinase, a 47 kDa secreted protein of hemolytic strains of streptococci, is a human plasminogen activator and contains three structural domains linked by flexible loops. We describe here the crystal structure of the isolated streptokinase middle (SKbeta) domain determined at 2.4 A resolution. Among the functionally important structural features is a putative binding site for a kringle domain of plasminogen located at the tip of a fully exposed hairpin loop. The distribution of genetically conserved residues of SKbeta is strongly correlated with their functions. The extensive interface of the SKbeta dimer suggests that such dimers may also exist in solution for free SKbeta.

Amino Acid Sequence↗
PubMed1999

Cloning and characterization of cDNA encoding cardosin A, an RGD-containing plant aspartic proteinase.

Cardosin A is an abundant aspartic proteinase from pistils of Cynara cardunculus L. whose milk-clotting activity has been exploited for the manufacture of cheese. Here we report the cloning and characterization of cardosin A cDNA. The deduced amino acid sequence contains the conserved features of plant aspartic proteinases, including the plant-specific insertion (PSI), and revealed the presence of an Arg-Gly-Asp (RGD) motif, which is known to function in cell surface receptor binding by extracellular proteins. Cardosin A mRNA was detected predominantly in young flower buds but not in mature or senescent pistils, suggesting that its expression is likely to be developmentally regulated. Procardosin A, the single chain precursor, was found associated with microsomal membranes of flower buds, whereas the active two-chain enzyme generated upon removal of PSI is soluble. This result implies a role for PSI in promoting the association of plant aspartic proteinase precursors to cell membranes. To get further insights about cardosin A, the functional relevance of the RGD motif was also investigated. A 100-kDa protein that interacts specifically with the RGD sequence was isolated from octyl glucoside pollen extracts by affinity chromatography on cardosin A-Sepharose. This result suggests that the 100-kDa protein is a cardosin A receptor and indicates that the interaction between these two proteins is apparently mediated through RGD recognition. It is possible therefore that cardosin A may have a role in adhesion-mediated proteolytic mechanisms involved in pollen recognition and growth.

Amino Acid Sequence↗
PubMed1999

SLAP, a dimeric adapter protein, plays a functional role in T cell receptor signaling.

Engagement of the T cell antigen receptor (TCR) leads to rapid activation of protein tyrosine kinases, which in turn phosphorylate downstream enzymes and adapter proteins. Some adapter proteins, such as SLP-76, Vav, and LAT, positively regulate TCR-mediated signal transduction, whereas others, such as Cbl, play an inhibitory role. SLAP (Src-like adapter protein), an adapter protein containing a Src homology 3 and a Src homology 2 domain, was isolated from a yeast interacting screen by using N-terminal Cbl as bait. N-terminal Cbl interacts with SLAP in vivo and in vitro in a tyrosine phosphorylation-independent manner. We observed that SLAP is expressed in T cells, and upon TCR activation, SLAP interacts with ZAP-70, Syk, LAT, and TCRzeta chain in Jurkat T cells. In transiently transfected COS-7 cells, SLAP forms separate complexes with ZAP-70, Syk, and LAT through its Src homology 2 domain. Overexpression of a C-terminal-truncated SLAP mutant down-regulates nuclear factor of activated T cells-AP1 activity. We have evidence that SLAP forms homodimers through its C-terminal region. Serial truncations and mutations in the C terminus of SLAP demonstrate that there is a correlation between the loss of dimerization and the inhibition of nuclear factor of activated T cells-AP1 activity. The in vivo association of SLAP with key signaling molecules and its inhibition of T cell activation suggests that SLAP plays an important role in TCR-mediated signal transduction.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Unusual sites of arginine methylation in Poly(A)-binding protein II and in vitro methylation by protein arginine methyltransferases PRMT1 and PRMT3.

Arginine methylation is a post-translational modification found mostly in RNA-binding proteins. Poly(A)-binding protein II from calf thymus was shown by mass spectrometry and sequencing to contain NG, NG-dimethylarginine at 13 positions in its amino acid sequence. Two additional arginine residues were partially methylated. Almost all of the modified residues were found in Arg-Xaa-Arg clusters in the C terminus of the protein. These motifs are distinct from Arg-Gly-Gly motifs that have been previously described as sites and specificity determinants for asymmetric arginine dimethylation. Poly(A)-binding protein II and deletion mutants expressed in Escherichia coli were in vitro substrates for two mammalian protein arginine methyltransferases, PRMT1 and PRMT3, with S-adenosyl-L-methionine as the methyl group donor. Both PRMT1 and PRMT3 specifically methylated arginines in the C-terminal domain corresponding to the naturally modified sites.

Amino Acid Sequence↗
PubMed1999

Crystal structure of human cytosolic phospholipase A2 reveals a novel topology and catalytic mechanism.

Cytosolic phospholipase A2 initiates the biosynthesis of prostaglandins, leukotrienes, and platelet-activating factor (PAF), mediators of the pathophysiology of asthma and arthritis. Here, we report the X-ray crystal structure of human cPLA2 at 2.5 A. cPLA2 consists of an N-terminal calcium-dependent lipid-binding/C2 domain and a catalytic unit whose topology is distinct from that of other lipases. An unusual Ser-Asp dyad located in a deep cleft at the center of a predominantly hydrophobic funnel selectively cleaves arachidonyl phospholipids. The structure reveals a flexible lid that must move to allow substrate access to the active site, thus explaining the interfacial activation of this important lipase.

Animals↗
PubMed1999

CH5+: the infrared spectrum observed

Protonated methane, CH5+, has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. Although many theoretical papers have been published on the quantum mechanics of the system, a better understanding requires spectral data. A complex, high-resolution infrared spectrum of CH5+ corresponding to the C-H stretching band in the 3.4-micrometer region is reported. Although no detailed assignment of the individual lines was made, comparison with other carbocation spectra strongly suggests that the transitions are due to CH5+.

Journal Article↗
PubMed1999

HLA class I homozygosity accelerates disease progression in human immunodeficiency virus type 1 infection.

Polymorphic products of HLA class I genes restrict cytotoxic T lymphocyte responses to the constantly evolving spectrum of HIV-1 antigens. Accordingly, homozygosity at class I loci can reduce the repertoire for such HLA-dependent interactions, leading to accelerated disease progression. To test this hypothesis we studied subjects from two distinct HIV/AIDS cohorts: 140 Dutch homosexual men and 202 Rwandan heterosexual women followed up to 13 years from HIV-1 seroconversion. We performed intermediate- and selective high-resolution molecular typing at HLA class I (A, B, and C) and high-resolution typing at HLA class II DRB1 and DQB1. Homozygosity at the HLA-A or -B locus or both was found at increasingly high frequency among individuals with successively more rapid progression to late-stage HIV-1-related conditions. In the combined cohorts (n = 342) the odds ratio (OR) due to HLA-A or -B antigen homozygosity in rapid versus slow progressors was 3.8 (p = 0.003); for Dutch men alone the OR was 3.5 (p = 0.102), and for Rwandan women the OR was 4.1 (p = 0.009). In contrast, homozygous genotypes at either HLA-C, DRB1, or DQB1 alone, or DRB1-DQB1 haplotypes, did not exert any deleterious effect on HIV-1 disease progression. These findings suggest strongly that diversity in addition to sequence specificity at HLA-A and -B loci can influence the rate of disease progression following HIV-1 infection.

Cohort Studies↗
PubMed1999

Biased TCR repertoire in infiltrating lesional T cells in human Bancroftian filariasis.

To investigate the hypothesis that T cells recognizing specific Ags localize to the site of disease activity in human bancroftian filariasis, we have compared the repertoire of TCR Vbeta gene segments in lesions vs blood in individual patients by RT-PCR ELISA. Vbeta14 and Vbeta24 were overrepresented (5% greater in tissue compared with PBMCs and/or tissue/PBMC ratios in the highest 5% of all tissue/PBMC ratios for all Vbetas for all subjects) in 50% and 40% of study subjects, respectively. Overrepresentation of these two Vbetas did not occur in any control subject. In comparing three patient groups, the proportion of individuals meeting at least one criterion for Vbeta14 overrepresentation was shown to increase in tandem with our current concepts of disease progression (asymptomatic filariasis = 25%; clinical filariasis with active infection = 60%; clinical filariasis without active infection = 71%). In 6 of the 10 individuals with Vbeta14 overrepresentation, Vbeta14 represented >20% of the entire lesional Vbeta repertoire. All but one of the 20 study subjects had at least one Vbeta gene segment that was overrepresented in tissue compared with PBMCs. Only a small number of Vbetas, usually three or less, were overrepresented in any single filariasis patient. However, in the same tissue, no differences between patient groups were found when IFN-gamma, TNF-alpha, IL-4, IL-5, and IL-12 mRNA expression were examined. Taken together, these findings suggest that, in principle, in essentially all patients, whether with subclinical or with clinical filariasis, distinct and limited T cell populations are concentrated in affected tissue.

Animals↗
PubMed1999

Glut1 and glut3 expression, but not capillary density, is increased by cobalt chloride in rat cerebrum and retina.

Treatment of rats with cobalt chloride [Co(II)], an agent that stimulates the expression of a set of hypoxia-responsive genes, for 10-12 days resulted in 1.45- and 1.40-fold increases in the content of Glut1 mRNA and Glut1 in cerebral gray matter, respectively (P<0. 05 for both changes). The increase in Glut1 content was associated with a significant increase in the content of Glut1 staining in microvessels isolated from cerebral gray matter, and in the intensity of Glut1 in microvessels of the frontal lobe and hippocampus assessed by immunohistochemistry. The abundance of Glut3 in cerebrum of Co(II)-treated rats also increased by 1.3-fold (P<0. 05), but the increase was not associated with a change in the content of Glut3 mRNA. In retina, treatment with Co(II) resulted in 2.48- and 1.23-fold increases in the content of Glut1 mRNA and Glut1 protein, respectively (P<0.05 for both changes); similar increases in Glut1 protein expression were observed in isolated retinal microvasculature. The content of Glut3 in retina also increased 1. 5-fold in Co(II)-treated rats (P<0.05). In addition, treatment with Co(II) resulted in a significant 2.2-fold increase in the expression of VEGF in the cerebrum. However, despite the Co(II)-induced increase in Glut1 expression in cerebral and retinal microvasculature and VEGF in cerebrum, there was no increase in the capillary density in either tissue. It is concluded that a 10-12 day exposure to Co(II), presumably acting through the hypoxia-signaling pathway, results in enhanced expression of both major glucose transporters in cerebral cortex and retina, without increasing the capillary density of either tissue.

Animals↗
PubMed1999

TFAR19, a novel apoptosis-related gene cloned from human leukemia cell line TF-1, could enhance apoptosis of some tumor cells induced by growth factor withdrawal.

Using the cDNA-representative differences analysis (cDNA-RDA) approach, we identified a novel gene, TFAR19 (TF-1 cell apoptosis related gene-19), from TF-1 cells undergoing apoptosis. The human TFAR19 encodes a protein which shares significant homology to the corresponding proteins of species ranging from yeast to mice. TFAR19 exhibits a ubiquitous expression pattern and its expression is upregulated in the tumor cells undergoing apoptosis. Overexpression of TFAR19 in tumor cells enhances apoptosis triggered by growth factor or serum deprivation. We propose that TFAR19 may play a general role in the apoptotic process.

Amino Acid Sequence↗
PubMed1999

Biliary structures lead to tumour recurrences after laser-induced interstitial thermotherapy.

BACKGROUND AND OBJECTIVE: Thermal diffusion during laser-induced interstitial thermotherapy (LITT) has not yet been fully investigated in heterogeneous tissue architecture such as liver. LITT was performed on rabbit liver tumours to analyse the role of biliary structures in thermal diffusion. STUDY DESIGN/MATERIALS AND METHODS: Twenty-four VX2 tumours were grafted onto 12 rabbit livers. The animals were randomly separated into two groups when tumour size reached 8 mm. Thermotherapy was performed by delivering the 830-nm output of a diode laser to the centre of the tumour with a 300-,microm fibre. Irradiation conditions were 1.5 W over 900 sec. On day 7 or 14, the tumours were removed and stained with haematoxylin-eosin and picrosirius red F3BA (PR). Thermal damage was evaluated by PR and electron microscopic examinations. RESULTS: Among the treated tumours, recurrences were found both at the periphery (one on day 7, seven on day 14) and within the treated area (two on day 7, two on day 14). All recurrences were located in the vicinity of the biliary structures, which are frequently spared from thermal injury. CONCLUSION: Biliary ducts lead to a heat sink, thereby facilitating tumour recurrences.

Animals↗
PubMed1999

Detoxication of paraoxon by rat liver homogenate and serum carboxylesterases and A-esterases.

Paraoxon, the active metabolite of parathion, can be detoxified through a noncatalytic pathway by carboxylesterases and a catalytic pathway by calcium-dependent A-esterases, producing p-nitrophenol as a common metabolite. The detoxication patterns of carboxylesterases and A-esterases were investigated in vitro in the present study with a high tissue concentration (75 mg/mL rat liver homogenate or 50% rat serum solution) to more closely reflect enzyme concentrations in intact tissues. A final paraoxon concentration of 3.75 microM was used to incubate with liver homogenates or serum solutions for 5 seconds or 3, 5, 15, or 25 minutes; also 0.625, 1.25, 2.5, 3.125, 3.75, or 5.0 microM paraoxon (final concentration) was incubated with liver homogenates or serum solutions for 15 minutes. Phenyl saligenin cyclic phosphate and EDTA were used to inhibit carboxylesterases and A-esterases, respectively. Significant amounts of p-nitrophenol were generated with or without either inhibitor during a 15 minute incubation with paraoxon from low (0.625 microM) to high (5.0 microM) concentrations. The amount of p-nitrophenol generated via carboxylesterase phosphorylation was greater than via A-esterase-mediated hydrolysis in the initial period of incubation or when incubating with a low concentration of paraoxon. Plateau shape curves of p-nitrophenol concentration versus time or paraoxon concentration indicated that carboxylesterase phosphorylation was saturable. When incubated for long time intervals or with high concentrations of paraoxon, more p-nitrophenol was generated via A-esterase-mediated hydrolysis than from carboxylesterase phosphorylation. The ratio of paraoxon concentration to tissue amount used in in vitro assays of this study was equivalent to dosing a rat with toxicologically relevant dosages. These in vitro data suggest that both carboxylesterases and A-esterases detoxify paraoxon in vivo; carboxylesterases may be an important mode of paraoxon detoxication in initial exposures to paraoxon or parathion before they become saturated, whereas A-esterases may contribute to paraoxon detoxication in repeated exposures to paraoxon or parathion because they will not become inhibited and will remain catalytically active unlike the carboxylesterases. The importance of carboxylesterases in detoxication of paraoxon was verified by an in vivo study. In rats pretreated with tri-o-tolyl phosphate, an in vivo carboxylesterase inhibitor, brain acetylcholinesterase was significantly inhibited after intravenous exposure to parathion. No significant inhibition of brain acetylcholinesterase was observed in rats pretreated with corn oil.

Acetylcholinesterase↗
PubMed1999

Infrared Spectroscopy of H3O+: The nu1 Fundamental Band.

The infrared spectrum of H3O+ in positive column discharges of H2/O2 gas mixtures has been studied by a difference frequency laser spectrometer. The nu1 fundamental band of H3O+ was identified in the region of the strong. Molecular constants were obtained by the least-squares fitting of the observed frequencies, and band origins of the and subbands were determined to be 3389.656(2) and 3491.170(2) cm-1, respectively. During this study, assignment of the nu3 fundamental band was extended to higher J, K transitions, which do not fit to the calculated pattern well, but have definitely been assigned by using the ground state combination differences and relative intensities. Vibration-rotation interactions between the nu1 and nu3 states have been considered, which explained some large discrepancies between observed and calculated frequencies and led to the identification of forbidden transitions. Energy differences in the ground state between the DeltaK = 3 rotational levels were obtained from the combination differences of the forbidden and allowed transitions, which led to an accurate determination of C and DK. Equilibrium structure of H3O+ has been derived to be re = 0.974(1) Å and alphae = 113.6(1) degrees. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Effect of terazosin on blood pressure and serum lipids.

In an open multicenter prospective study, the effects of short-term (4 weeks, n = 101) and long-term (6 months, n = 38) terazosin treatment on blood pressure, serum lipids and safety in the patients with mild to moderate essential hypertension were observed. Mean systolic and diastolic blood pressure in sitting position were significantly reduced by 16.4% and 14.0% respectively (P < 0.01) after 4 weeks of terazosin therapy, with the total efficacy rate being 87.1%. During a 6 month therapy, antihypertensive effect of terazosin could be maintained. Total cholesterol (TC) and low density lipoprotein (LDL) cholesterol in serum were significantly decreased P < 0.05-0.01) in patients with hypercholesterolemia (TC > or = 6 mmol/ml) after 4 week terazosin treatment; the levels of TC, LDL and triglyceride were significantly improved in hypertensive patients after 3-6 month terazosin treatment. The improvement of lipid metabolism was related to the dosage of terazosin but not to antihypertensive effects of terazosin. The results suggested that terazosin is effective in decreasing blood pressure and improving lipid metabolism. It may serve as a good antihypertensive agent for hypertensive patients with hypercholesterolemia.

Antihypertensive Agents↗