Biomedical subjects

S X Wang

Publications and source records attributed to S X Wang.

At least 19 recordsLinked to original sources

PubMed2002

Early identification of Mycobacterium tuberculosis complex in BACTEC cultures by ligase chain reaction.

A total of 1431 acid-fast bacilli (AFB) in Bactec culture vials from 1427 patients was differentiated by the Bactec NAP method and tested by the LCx Mycobacterium tuberculosis ligase chain reaction system. In all, 1321 of 1325 M. tuberculosis complex (MTBC) isolates were correctly detected by the LCx assay. All the 106 non-tuberculous mycobacteria (NTM) isolates were negative by the LCx assay. No false MTBC-positive result was obtained from NTM isolates. However, the LCx assay failed to detect four MTBC isolates from one patient. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 99.7, 100%, 100% and 96.4%, respectively. These data suggest that the LCx system can be used to identify MTBC in AFB-positive Bactec broth cultures when the growth index is > or = 100. The method gives a 100% PPV and allows a faster turnaround time for MTBC than the NAP test.

Humans↗

PubMed2001

Nanoscale manipulation of pyrochlore: new nanocomposite ionic conductors.

The ionic conductivity of isometric pyrochlore, ideally A2B2O (7), is extremely sensitive to disordering of A- and B-site cations and oxygen anion vacancies. We report the first use of ion beam irradiation-induced disordering in Gd 2Ti 2O (7) to produce a strain-free, buried, disordered defect-fluorite layer approximately 12 nm thick within an ordered pyrochlore matrix. This approach provides a new means of creating nanoscale, mixed ionic-electronic conductors in pyrochlore ceramics, such as those required for solid-state electrochemical cells.

Journal Article↗

PubMed2001

Crystal structure of thrombin-ecotin reveals conformational changes and extended interactions.

The protease inhibitor ecotin fails to inhibit thrombin despite its broad specificity against serine proteases. A point mutation (M84R) in ecotin results in a 1.5 nM affinity for thrombin, 10(4) times stronger than that of wild-type ecotin. The crystal structure of bovine thrombin is determined in complex with ecotin M84R mutant at 2.5 A resolution. Surface loops surrounding the active site cleft of thrombin have undergone significant structural changes to permit inhibitor binding. Particularly, the insertion loops at residues 60 and 148 in thrombin, which likely mediate the interactions with macromolecules, are displaced when the complex forms. Thrombin and ecotin M84R interact in two distinct surfaces. The loop at residue 99 and the C-terminus of thrombin contact ecotin through mixed polar and nonpolar interactions. The active site of thrombin is filled with eight consecutive amino acids of ecotin and demonstrates thrombin's preference for specific features that are compatible with the thrombin cleavage site: negatively charged-Pro-Val-X-Pro-Arg-hydrophobic-positively charged (P1 Arg is in bold letters). The preference for a Val at P4 is clearly defined. The insertion at residue 60 may further affect substrate binding by moving its adjacent loops that are part of the substrate recognition sites.

Amino Acid Sequence↗

PubMed2001

The role of ecotin dimerization in protease inhibition.

Ecotin is a homodimeric protein from Escherichia coli that inhibits many serine proteases of the chymotrypsin fold, often with little effect from the character or extent of enzyme substrate specificity. This pan-specificity of inhibition is believed to derive from formation of a heterotetrameric complex with target proteases involving three types of interface: the dimerization interface, a primary substrate-like interaction, and a smaller secondary interaction between the partner ecotin subunit and the protease. A monomeric ecotin variant (mEcotin) and a single-chain ecotin dimer (scEcotin) were constructed to study the effect of a network of protein interactions on binding affinity and the role of dimerization in broad inhibitor specificity. mEcotin was produced by inserting a beta-turn into the C-terminal arm, which normally exchanges with the other subunit. While the dimerization constant (K(dim)) of wild-type (WT) ecotin was found to be picomolar by subunit exchange experiments using FRET and by association kinetics, mEcotin was monomeric up to 1 mM as judged by gel filtration and analytical centrifugation. A crystal structure of uncomplexed mEcotin to 2.0 A resolution verifies the design, showing a monomeric protein in which the C-terminal arm folds back onto itself to form a beta-barrel structure nearly identical to its dimeric counterpart. The kinetic rate constants and equilibrium dissociation constants for monomeric and dimeric ecotin variants were determined with both trypsin and chymotrypsin. The effect of the secondary binding site on affinity was found to vary inversely with the strength of the interaction at the primary site. This compensatory effect yields a nonadditivity of up to 5 kcal/mol and can be explained in terms of the optimization of binding orientation. Such a mechanism of adaptability allows femtomolar affinities for two proteases with very different specificities.

Bacterial Proteins↗

PubMed2001

Precursor of a novel scorpion venom peptide (BmKn1) with no disulfide bridge from Buthus martensii Karsch.

A full-length cDNA sequence encoding the precursor of a novel venom peptide (named BmKn1) with no disulfide bridge was first isolated from the venom gland cDNA library of Chinese scorpion Buthus martensii Karsch. The encoded precursor consisted of 70 amino acid residues including two parts: a signal peptide of 23 residues, and a putative mature venom peptide (BmKn1) of 47 residues. The sequence of BmKn1 showed no similarity to those of other scorpion venom peptides. BmKn1 may be the first member of a new venom peptide family from scorpion. Future research will be interesting to unravel further the pharmacological function of this novel scorpion venom peptide.

Amino Acid Sequence↗

PubMed2001

Recurrence of nephrotic syndrome after transplantation in CNF is due to autoantibodies to nephrin.

The novel gene NPHS1 is defective in the patients with congenital nephrotic syndrome of the Finnish type (CNF) leading to abnormal expression of the respective protein product nephrin in glomerular cells. CNF patients are treated with early nephrectomy and renal transplantation, but about 20% show recurrence of nephrotic syndrome (NS). We used indirect immunofluorescence microscopy and immunoblotting and an ELISA assay to search for circulating autoantibodies to nephrin, the protein defect in CNF patient kidneys. In serial serum samples gathered before and after recurrence of NS, we show an increased antibody titer to nephrin prior to the NS episode and a subsequent drop in antibody level after its successful treatment and reactivity of the high titer sera with glomeruli in indirect immunofluorescence microscopy as well. The results show that the transplantation treatment introduces a neoantigen inducing production of autoantibodies, which may be pathogenic for perturbation of the function of the glomerular filtration barrier.

Amino Acid Sequence↗

PubMed2001

Influence of fuel quality on vehicular NOx emissions.

The quality of gasoline and diesel fuel affects pollutant emissions from vehicles. By applying the COMPLEX model, developed by the US EPA and industry to relate fuel composition to vehicle emissions, this paper estimates the influence of improvements in gasoline quality to lower vehicular NOx emissions. A case study is performed for Guangzhou City that has NOx concentrations significantly above the national ambient air quality standards(NAAQS). The paper discusses the potential for reducing NOx in Guangzhou by improving the quality of gasoline.

Air Pollutants↗

PubMed2001

Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant.

This paper describes an atmospheric dispersion field experiment performed on the coastal site of nuclear power plant in the east part of China during 1995 to 1996. The three-dimension joint frequency are obtained by hourly observation of wind and temperature on a 100 m high tower; the frequency of the "event day of land and sea breezes" are given by observation of surface wind and land and sea breezes; the diffusion parameters are got from measurements of turbulent and wind tunnel simulation test. A new model calculating the annual mean atmospheric dispersion factor for coastal site of nuclear power plant is developed and established. This model considers not only the effect from mixing release and mixed layer but also the effect from the internal boundary layer and variation of diffusion parameters due to the distance from coast. The comparison between results obtained by the new model and current model shows that the ratio of annual mean atmospheric dispersion factor gained by the new model and the current one is about 2.0.

Air Pollutants, Occupational↗

PubMed2001

[Determination of naoning pian by multi-wavelength linear regression method].

Assay of naoning pian was reported by multi-wavelength linear regression method in this paper. The program was edited by BASIC. The recoveries and RSD of pyramidon and caffeine were 98.03%-100.9%, 1.0% and 97.77%-99.39%, 0.61%, respectively. This method could be used for the determination of two components in naoning pian without separation. The method was simple, rapid, and results were satisfactory.

Analgesics, Non-Narcotic↗

PubMed2000

Activation of Xenopus Chk1 by mutagenesis of threonine-377.

Xenopus Chk1 (Xchk1) is required for the checkpoint-associated delay of the cell cycle in frog egg extracts containing unreplicated or UV-damaged DNA. Phosphorylation of Xchk1 at multiple sites in the SQ/TQ domain (residues 314-366) in response to unreplicated or UV-damaged DNA results in elevation of its kinase activity. We have found that mutagenesis of Thr-377 in the conserved Thr-Arg-Phe (TRF) motif of Xchk1 also leads to a substantial increase in kinase activity. Thr-377 does not appear to be a site of phosphorylation in Xchk1. These findings suggest that Thr-377 may play a role in suppressing the activity of Xchk1.

Amino Acid Sequence↗

PubMed2000

Requirement for Atr in phosphorylation of Chk1 and cell cycle regulation in response to DNA replication blocks and UV-damaged DNA in Xenopus egg extracts.

The checkpoint kinase Xchk1 becomes phosphorylated in Xenopus egg extracts in response to DNA replication blocks or UV-damaged DNA. Xchk1 is also required for the cell cycle delay that is induced by unreplicated or UV-damaged DNA. In this report, we have removed the Xenopus homolog of ATR (Xatr) from egg extracts by immunodepletion. In Xatr-depleted extracts, the checkpoint-associated phosphorylation of Xchk1 is abolished, and the cell cycle delay induced by replication blocks is strongly compromised. Xatr from egg extracts phosphorylated recombinant Xchk1 in vitro, but not a mutant form of Xchk1 (Xchk1-4AQ) containing nonphosphorylatable residues in its four conserved SQ/TQ motifs. Recombinant human ATR, but not a kinase-inactive mutant, phosphorylated the same sites in Xchk1. Furthermore, the Xchk1-4AQ mutant was found to be defective in mediating a checkpoint response in egg extracts. These findings suggest that Xchk1 is a functionally important target of Xatr during a checkpoint response to unreplicated or UV-damaged DNA.

Amino Acid Motifs↗

PubMed2000

Membrane-induced conformational change in human apolipoprotein H.

The interaction of apolipoprotein H (Apo H) with lipid membrane has been considered to be a basic mechanism for the biological function of the protein. Previous reports have demonstrated that Apo H can interact only with membranes containing anionic phospholipids. Here we study the membrane-induced conformational change of Apo H by CD spectroscopy with two different model systems: anionic-phospholipid-containing liposomes [such as 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) and cardiolipin], and the water/methanol mixtures at moderately low pH, which mimic the micro-physicochemical environment near the membrane surface. It is found that Apo H undergoes a remarkable conformational change on interaction with liposomes containing anionic phospholipid. To interact with liposomes containing DMPG, there is a 6.8% increase in alpha-helix in the secondary structures; in liposomes containing cardiolipin, however, there is a 12.6% increase in alpha-helix and a 9% decrease in beta-sheet. The similar conformation change in Apo H can be induced by treatment with an appropriate mixture of water/methanol. The results indicate that the association of Apo H with membrane is correlated with a certain conformational change in the secondary structure of the protein.

Cell Membrane↗

PubMed2000

Nephrin in experimental glomerular disease.

BACKGROUND: The recently identified gene NPHS1 with its mutations causing congenital nephrotic syndrome of the Finnish type (CNF) is highly promising in providing new understanding of pathophysiology of proteinuria. Earlier we cloned a rat NPHS1 homologue, as well as characterized and raised antibodies to the respective protein product nephrin. METHODS: Changes in the expression levels of nephrin-specific mRNA in commonly used experimental models of proteinuria were examined using semiquantitative reverse transcription-polymerase chain reaction, immunofluorescence, and immunoelectron microscopy (IEM) of nephrin. RESULTS: Notably, a 40% down-regulation of the nephrin-specific mRNA of cortical kidney was seen already at day 3 after induction of the puromycin aminonucleoside nephrosis (PAN), while no major elevation of urinary protein secretion was seen at this stage. A further decrease of 80% of nephrin message was seen at the peak of proteinuria at day 10. A similar decrease of up to 70% from the basal levels was seen in mercuric chloride-treated rats. Changes in the protein expression paralleled those of the mRNA in indirect immunofluorescence. Interestingly, a remarkable plasmalemmal dislocation from the normal expression site at the interpodocyte filtration slits could be observed in IEM. CONCLUSIONS: Nephrin appears to be an important causative molecule of proteinuria and shows a remarkable redistribution from the filtration slits to the podocyte plasma membrane, especially in PAN.

Albuminuria↗

PubMed2000

Conscious sedation and cardiorespiratory safety during colonoscopy.

BACKGROUND: Cardiorespiratory events during colonoscopy are common. The effect of sedative premedication on cardiorespiratory parameters during colonoscopy has not been studied in controlled, prospective trials. METHODS: One hundred eighty patients undergoing colonoscopy were divided into 3 groups: (1) sedation with intravenous midazolam (midazolam group); (2) sedation with intravenous saline (placebo group); and (3) no intravenous cannula (control group). Arterial oxygen saturation (SaO(2)), systolic and diastolic blood pressure and continuous electrocardiogram were recorded prior to, during and after the endoscopic procedure. RESULTS: Midazolam produced lower SaO(2) values during colonoscopy compared with placebo or control groups (p < 0.001, repeated measures analysis of variance). Systolic and diastolic blood pressure during colonoscopy were lower in the midazolam group than in the placebo group (p < 0.01 and p < 0.05, respectively), but no difference was found between the midazolam and the control groups. Hypotension (systolic blood pressure less than 100 mm Hg) occurred more frequently in the midazolam group (19%) than in the placebo (3%; p < 0.01) or control groups (7%; p < 0.05). ST-segment depression developed in 7% of patients during the recording with no difference between the groups. In 75% of cases ST-depression appeared prior to the endoscopic procedure. CONCLUSIONS: Premedication with midazolam induced a statistically significant decrease in arterial oxygen saturation and increased the risk for hypotension. However, colonoscopy proved to be a safe procedure both with and without sedation.

Adult↗

PubMed2000

Effect of conscious sedation on cardiac autonomic regulation during colonoscopy.

BACKGROUND: Colonoscopy is associated with cardiovascular events including hypotension, hypertension, and myocardial ischemia. The pathogenetic mechanisms of these cardiovascular events are unknown, but there is evidence that the autonomic nervous system may play a role. Conscious sedation is often used to relieve the inconvenience caused by the procedure. In this study, we evaluated the effects of sedation on cardiac autonomic regulation during colonoscopy. METHODS: One hundred and eighty patients undergoing elective colonoscopy were prospectively randomized into three groups: (i) sedation with intravenous midazolam (midazolam group); (ii) sedation with intravenous saline (placebo group); and (iii) no intravenous cannula (control group). Continuous electrocardiogram was recorded prior to, during, and after the colonoscopic procedure. Heart rate variability (HRV) was assessed by means of the power spectral analysis; the powers of low-frequency (LF 0.04-0.15 Hz) and high-frequency (HF 0.15-0.40 Hz) components were calculated. RESULTS: Intubation of the colonoscope increased the LF component of HRV and decreased HF power in all study groups compared to baseline recording. Furthermore, compared to baseline, the LF/HF ratio--a marker of cardiac sympathetic regulation--increased during intubation in the midazolam (P < 0.001) and placebo (P < 0.05) groups, with no change in the control group. During intubation the midazolam group presented with higher LF and lower HF power than placebo (P < 0.001) and control groups (P < 0.01). Accordingly, the LF/HF ratio was higher in the midazolam group than in the placebo (P < 0.05) or control groups (P < 0.05). CONCLUSIONS: Midazolam potentiates the dominance of the sympathetic nervous system induced by colonoscopy. Therefore, conscious sedation with midazolam may contribute to the occurrence of cardiovascular events during colonoscopy.

Colonoscopy↗

PubMed2000

A new phytoecdysone from the roots of Rhaponticum uniflorum.

A new ecdysteroid named rhapontisterone R1 (1) together with two known phytoecdysones, rhapontisterone (2) and ecdysterone (3) were isolated from the roots of Rhaponticum uniflorum (L.) DC. The new compound was shown to be 2beta,3beta,11alpha,14alpha,20xi,22xi-hexahydroxy-stigma-7,24(28)-dien-6-oxo-28,25-carbolactone. The structure has been determined primarily on the basis of physico-chemical properties and spectral analysis.

Chromatography, High Pressure Liquid↗

PubMed2000

Isolation and purification of functional total RNA from woody branches and needles of Sitka and white spruce.

The isolation of intact, functional RNA from conifer spp. is not easy, especially from those tissues that are heavily lignified and characterized by a low number of living cells. An efficient procedure for isolating RNA from combined wood and bark tissues of conifers was developed based on a protocol optimized for the extraction of RNA from pollen and one for the isolation of RNA from woody stems. This protocol does not involve the use of phenol, and no ultracentrifugation was required. In addition, the protocol overcame the problems of RNA degradation and low yield due to oxidation by polyphenolics and co-precipitation with polysaccharides, both of which are abundant components in conifer bark tissues. The isolated RNA was of high quality and undegraded as gauged by spectrophotometric readings and electrophoresis in denaturing agarose gels. Quality was further assessed through the subsequent use of the RNA in reverse transcription and RT-PCR, indicating that it could be used for a number of downstream purposes including Northern blot hybridization and cDNA library construction. Using this modified protocol, 80-150 micrograms of RNA was routinely obtained from 1 g of fresh material. This protocol was also used for the isolation of RNA from needles of spruce spp., from which 750-950 micrograms RNA per gram of starting material could routinely be obtained.

Base Sequence↗

PubMed1999

The xenopus Suc1/Cks protein promotes the phosphorylation of G(2)/M regulators.

The entry into mitosis is controlled by Cdc2/cyclin B, also known as maturation or M-phase promoting factor (MPF). In Xenopus egg extracts, the inhibitory phosphorylations of Cdc2 on Tyr-15 and Thr-14 are controlled by the phosphatase Cdc25 and the kinases Myt1 and Wee1. At mitosis, Cdc25 is activated and Myt1 and Wee1 are inactivated through phosphorylation by multiple kinases, including Cdc2 itself. The Cdc2-associated Suc1/Cks1 protein (p9) is also essential for entry of egg extracts into mitosis, but the molecular basis of this requirement has been unknown. We find that p9 strongly stimulates the regulatory phosphorylations of Cdc25, Myt1, and Wee1 that are carried out by the Cdc2/cyclin B complex. Overexpression of the prolyl isomerase Pin1, which binds to the hyperphosphorylated forms of Cdc25, Myt1, and Wee1 found at M-phase, is known to block the initiation of mitosis in egg extracts. We have observed that Pin1 specifically antagonizes the stimulatory effect of p9 on phosphorylation of Cdc25 by Cdc2/cyclin B. This observation could explain why overexpression of Pin1 inhibits mitotic initiation. These findings suggest that p9 promotes the entry into mitosis by facilitating phosphorylation of the key upstream regulators of Cdc2.

Adaptor Proteins, Signal Transducing↗