Search PubMed⌕ Search

Biomedical subjects

W W Dai

Publications and source records attributed to W W Dai.

14 recordsLinked to original sources
PubMed2001

CD147 is a signaling receptor for cyclophilin B.

Cyclophilins A and B (CyPA and CyPB) are cyclosporin A binding proteins that can be secreted in response to inflammatory stimuli. We recently identified CD147 as a cell-surface receptor for CyPA and demonstrated that CD147 is an essential component in the CyPA-initiated signaling cascade that culminates in ERK activation and chemotaxis. Here we demonstrate that CD147 also serves as a receptor for CyPB. CyPB induced Ca(2+) flux and chemotaxis of CD147-transfected, but not control, CHO cells, and the chemotactic response of primary human neutrophils to CyPB was blocked by antibodies to CD147. These results suggest that CD147 serves as a receptor for extracellular cyclophilins.

Animals↗
PubMed2000

Lipopolysaccharide inhibits HIV-1 infection of monocyte- derived macrophages through direct and sustained down-regulation of CC chemokine receptor 5.

It is now well established that HIV-1 requires interactions with both CD4 and a chemokine receptor on the host cell surface for efficient infection. The expression of the CCR5 chemokine receptor in human macrophages facilitates HIV-1 entry into these cells, which are considered important in HIV pathogenesis not only as viral reservoirs but also as modulators of altered inflammatory function in HIV disease and AIDS. LPS, a principal constituent of Gram-negative bacterial cell walls, is a potent stimulator of macrophages and has been shown to inhibit HIV infection in this population. We now present evidence that one mechanism by which LPS mediates its inhibitory effect on HIV-1 infection is through a direct and unusually sustained down-regulation of cell-surface CCR5 expression. This LPS-mediated down-regulation of CCR5 expression was independent of de novo protein synthesis and differed from the rapid turnover of these chemokine receptors observed in response to two natural ligands, macrophage-inflammatory protein-1alpha and -1beta. LPS did not act by down-regulating CCR5 mRNA (mRNA levels actually increased slightly after LPS treatment) or by enhancing the degradation of internalized receptor. Rather, the observed failure of LPS-treated macrophages to rapidly restore CCR5 expression at the cell-surface appeared to result from altered recycling of chemokine receptors. Taken together, our results suggest a novel pathway of CCR5 recycling in LPS-stimulated human macrophages that might be targeted to control HIV-1 infection.

CCR5 Receptor Antagonists↗
PubMed1999

Detailed active site configuration of a new crystal form of methanol dehydrogenase from Methylophilus W3A1 at 1.9 A resolution.

The three-dimensional structure of a new crystal form of methanol dehydrogenase from Methylophilus W3A1 has been obtained in the presence of substrate using data recorded at a synchrotron. The structure of this approximately 140 kDa heterotetramer, refined at 1. 9 A resolution, reveals the detailed configuration of its redox cofactor, pyrroloquinoline quinone (PQQ). C4, one of the oxygen-bearing atoms of this orthoquinone is in a planar configuration while C5, which bears the other quinone oxygen, is tetrahedral, suggesting that the PQQ is in the semiquinone redox state. The substrate binding site has been identified close to PQQ and to the side chain of Asp297, the putative active site base. The proximity of the hydroxyl of methanol to C5 of PQQ compared to the greater separation of the substrate methyl group from C5 supports the addition-elimination reaction mechanism involving a hemiketal intermediate.

Alcohol Oxidoreductases↗
PubMed1998

Methionine formation from alpha-ketomethiobutyrate in the trypanosomatid Crithidia fasciculata.

Methionine consumed during the synthesis of polyamines can be recycled in most organisms by a unique pathway wherein the final step is the transaminative conversion of alpha-ketomethiobutyrate to methionine (KMAT activity). In the trypanosomatid Crithidia fasciculata, three separate aminotransferases (KMAT-A, -B, -T) were found to catalyse this activity. All three aminotransferases were found to utilise aromatic amino acids as the amino donor for the KMAT reaction, but KMAT-A functioned optimally with histidine and KMAT-B with arginine as amino donors. KMAT-T was found to operate best with aromatic amino acids and glutamate as amino donors, and was also found to catalyse aspartate aminotransferase and tyrosine aminotransferase activities. Amino acid sequencing of internal peptides from KMAT-T yielded a sequence with very high identity to vertebrate, cytosolic aspartate aminotransferase. As pig heart cytosolic aspartate and alanine aminotransferases were found to be unable to catalyse KMAT activity, the crithidial enzyme appears to be an aspartate aminotransferase with unusual catalytic properties. Inhibition studies on C. fasciculata homogenates showed that carboxymethoxylamine, canaline, and nitrophenylalanine were effective inhibitors of total KMAT activity (63-100% inhibition at 1 mM in the presence of 1 mM alpha-ketomethiobutyrate and 30 mM total amino acid as substrates) and the individual, isolated enzymes. At 1 mg ml-1, canaline was found to inhibit cell growth in vitro by 62%, and carboxymethoxylamine caused cell death within 24 h.

Alanine↗
PubMed1997

Studies on the mechanism of antimalarial action of a novel arylene bis(methylketone).

2-Amino-4-(3,5-diacetylphenyl)amino-1,6-dimethylpyrimidinium chloride (CNI-H0294) is a novel arylene bis(methylketone) compound that displays antimalarial activity against chloroquine- and pyrimethamine-resistant Plasmodium falciparum clones. The compound has been found to be concentrated into infected erythrocytes, with 80-179 microM accumulated when parasites were cultured in the presence of 1.0 microM CNI-H0294. Uninfected erythrocytes, in contrast, only accumulated 2.5-3.4 microM CNI-H0294 under identical conditions. Using postmitochondrial supernatants from a number of parasite clones, the compound was found to inhibit dihydrofolate reductase (EC 1.5.1.3) activity with an IC50 of 243-483 microM. Thus, while CNI-H0294 is not a powerful inhibitor of plasmodial dihydrofolate reductase, the accumulation of the compound into infected erythrocytes, when correlated to the external ED50 concentration against parasite growth in vitro, reaches concentrations sufficient to inhibit the malarial enzyme.

Animals↗
PubMed1997

Studies on the pharmacological properties of novel arylene bis(methylketone) compounds using solid-phase extraction and high-performance liquid chromatography.

A method utilising solid-phase extraction followed by high-performance liquid chromatography has been developed to quantify novel arylene bis(methylketone) chemotherapeutics present in biological samples. The samples are extracted over cyanopropylsilane solid-phase extraction cartridges using 10 mM heptanesulfonate-10 mM tetramethylammonium chloride-4.2 mM H3PO4-95% CH3CN as the eluent. Analytical chromatography utilises a diisopropyl-C8 reversed-phase column and a 7.5-45% CH3CN gradient in 10 mM heptanesulfonate-10 mM tetramethylammonium chloride-4.2 mM H3PO4-H2O. Detection was by ultraviolet spectrophotometry at 300 or 240 nm. The linear response of the assay was found to extend from at least 100 microg/ml down to 97.66 ng/ml for a 100 microl injection. The assay system was utilised to determine the plasma kinetics of the compounds in mice, where all the drugs were found to display rapid absorption and elimination following intraperitoneal dosing. In vitro and in vivo studies of metabolism demonstrated that each of the compounds produced several metabolites, and that this conversion could be extensive in vivo.

Aniline Compounds↗
PubMed1997

Synergism of cimetidine with anti-malarial agents.

The histamine type-2 receptor antagonist and cytochrome P450 inhibitor cimetidine was examined for its antimalarial properties in the presence or absence of chloroquine or pyrimethamine. When used alone, cimetidine displayed little activity against a number of Plasmodium falciparum clones in vitro, with an IC50 of 300-700 microM. The compound was found to be highly synergistic in combination with chloroquine and also displayed a degree of synergism when used in combination with pyrimethamine. These synergistic effects were independent of the chloroquine- or pyrimethamine-resistance status of the clones. The cytochrome P450 inhibitor proadifen displayed weak synergism or antagonism with chloroquine, depending on the clone tested, and clear antagonism with pyrimethamine. The results with proadifen indicate that cimetidine was exerting its synergistic activity via a mechanism distinct from inhibition of cytochrome P450. Additional experiments have demonstrated that cimetidine interferes with neither plasmodial sterol metabolism nor heme polymerization.

Animals↗
PubMed1996

Aromatic amino acid transamination and methionine recycling in trypanosomatids.

Although trypanosomatids are known to rapidly transaminate exogenous aromatic amino acids in vitro and in vivo, the physiological significance of this reaction is not understood. In postmitochondrial supernatants prepared from Trypanosoma brucei brucei and Crithidia fasciculata, we have found that aromatic amino acids were the preferred amino donors for the transamination of alpha-ketomethiobutyrate to methionine. Intact C. fasciculata grown in the presence of [15N]tyrosine were found to contain detectable [15N]methionine, demonstrating that this reaction occurs in situ in viable cells. This process is the final step in the recycling of methionine from methylthioadenosine, a product of decarboxylated S-adenosylmethionine from the polyamine synthetic pathway. Mammalian liver, in contrast, preferentially used glutamine for this reaction and utilized a narrower range of amino donors than seen with the trypanosomatids. Studies with methylthioadenosine showed that this compound was readily converted to methionine, demonstrating a fully functional methionine-recycling pathway in trypanosomatids.

Amino Acids↗
PubMed1996

Antimalarial activity of novel arylene bis(methylketone) compounds.

Because of the spread of drug-resistant Plasmodium species, there is an urgent need for novel effective antimalarial agents. A series of arylene bis(methylketone) compounds were screened in vitro against a number of Plasmodium falciparum clones and in vivo against Plasmodium berghei. 2-amino-4-(3,5-diacetylphenyl)amino-1,6-dimethylpyrimidinium chloride (Cytokine Network Inc. [CNI]-H0294) was the most effective of the compounds in vitro, with an IC50 of 1.5-4.0 microM against parasite clones with a wide range of sensitivities to chloroquine and pyrimethamine. Other compounds in the series had in vitro IC50 values of 20-25 microM. In a 4-day test for suppression of P. berghei parasitemia in vivo, 50 mg/kg/day CNI-H0294 significantly decreased parasitemia by >90%. The compound was found to have low toxicity in mice, with an LD50 of 590 +/- 66 mg/kg intraperitoneally, and rapid plasma kinetics. These results show that CNI-H0294 has considerable antimalarial activity and merits further study.

Animals↗
PubMed1994

A direct sensitivity matrix approach for fast reconstruction in electrical impedance tomography.

In electrical impedance imaging, several proposed reconstruction algorithms have employed the concept of a sensitivity matrix, which can be used to relate the magnitude of a boundary voltage change of a 2D object to the change in conductivity inside the object that has given rise to it. The search for an appropriate inversion of the sensitivity matrix is the key to these algorithms. In this work, a method called the direct sensitivity matrix (DSM) approach for fast image reconstruction is proposed. Both theoretical and experimental results showing the efficiency of this proposed method are also presented.

Algorithms↗
PubMed1994

Using the Hilbert uniqueness method in a reconstruction algorithm for electrical impedance tomography.

This paper presents a new version of the layer stripping algorithm in the sense that it works essentially by repeatedly stripping away the outermost layer of the medium after having determined the conductivity value in this layer. In order to stabilize the ill posed boundary value problem related to each layer, we base our algorithm on the Hilbert uniqueness method (HUM) and implement it with the boundary element method (BEM).

Algorithms↗
PubMed1993

The active site structure of the calcium-containing quinoprotein methanol dehydrogenase.

Pyrroloquinoline quinone (PQQ), widely found in nature, serves as the redox cofactor in bacterial methanol dehydrogenase (MEDH), a heterotetrameric enzyme that oxidizes methanol to formaldehyde. The refined structure of MEDH at 2.4-A resolution, based on recently obtained amino acid sequence data, reveals that the PQQ, located in a central channel of the disk-shaped protein, is sandwiched between a Trp side chain and a very unusual vicinal disulfide. A Ca2+ ion forms a bridge between PQQ and the protein molecule, very close to a putative substrate binding pocket. The vicinal disulfide may form during PQQ incorporation and possibly act to hold the latter in place.

Alcohol Oxidoreductases↗
PubMed1992

The three-dimensional structures of methanol dehydrogenase from two methylotrophic bacteria at 2.6-A resolution.

The structures of methanol dehydrogenase (MEDH) from two closely related methylotrophic bacteria, Methylophilus methylotrophus and W3A1, have been determined at 2.6-A resolution. The molecule, a quinoprotein of molecular mass of about 138 kDa, contains two heavy (H) and two light (L) subunits of unknown sequence and two molecules of noncovalently associated pyrroloquinoline quinone. The two enzymes crystallize isomorphously in space group P2(1) with one H2L2 heterotetramer in the asymmetric unit. The electron density map of the M. methylophilus enzyme was obtained by multiple isomorphous replacement with anomalous scattering and improved by solvent leveling and electron density averaging. For model building, the amino acid sequence of MEDH from Paracoccus denitrificans for the H subunit and from Methylobacterium extorquens AM1 for the L subunit were used to represent the unknown amino acid sequence. At the present time, 579 and 57 amino acid residues for the large and small subunits, respectively, have been fitted into the map. The phases for MEDH from M. methylophilus were used directly to analyze the W3A1 structure, and both structures were refined to R-factors (where R = sigma[Fo-Fc[/sigma Fo) of 0.277 and 0.266, respectively. The L subunit contains a long alpha-helix and an extended N-terminal segment, both lying on the molecular surface of the H subunit. The H subunit contains eight antiparallel beta-sheets, each consisting of four strands arranged topologically like the letter W. The eight Ws are arranged circularly, forming the main disc-shaped body of the subunit, with some short helices and loops connecting the consecutive Ws, as well as some excursions within and between some of the Ws. The pyrroloquinoline quinone prosthetic group is located in the central channel of the large subunit near the surface of the molecule. The topology of the eight-W folding unit is similar to those of the six- and seven-W folding units previously reported for three other proteins, neuraminidase, methylamine dehydrogenase, and galactose oxidase.

Alcohol Oxidoreductases↗