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L Niu

Publications and source records attributed to L Niu.

At least 19 recordsLinked to original sources
PubMed2005

Morphological brain changes associated with Schneider's first-rank symptoms in schizophrenia: a MRI study.

BACKGROUND: Schneider's first-rank symptoms involve an alienated feature of the sense of one's own mental or physical activity. To clarify the brain morphological basis for the production of these symptoms, volumes of the frontal and medial temporal regions and their clinical correlates were examined in patients with schizophrenia. METHOD: Twenty-two patients with schizophrenia and 44 age- and gender-matched healthy control subjects were included. All patients were in their psychotic episodes with definite Schneiderian symptoms, rated by using the Scale for Assessment of Positive Symptoms. Volumetric measurements of high-resolution magnetic resonance imaging were performed in the prefrontal area, cingulate gyrus, and precentral gyrus, and the medial temporal structures such as the amygdala, hippocampus, and parahippocampal gyrus. RESULTS: Patients had significantly decreased volumes in the cingulate gray matter and the amygdala compared to controls. In the patient group, Schneiderian symptom severity showed significant inverse correlations with volumes of the right posterior cingulate gray matter and of the left anterior parahippocampal gyrus. CONCLUSIONS: Schneiderian symptoms may be associated with morphological abnormalities in the limbic-paralimbic regions such as the cingulate gyrus and parahippocampal gyrus, which possibly serve the self-monitoring function and the coherent storage and reactivation of information.

Adult↗
PubMed2001

Heterologous expression of the single-mutation glucose isomerase (GIG138P) gene in Streptomyces lividans and its genetic instability.

A 1.3-kb PstI-BamHI fragment containing the single-mutation glucose isomerase (GIG138P, GI1) gene and its natural promoter was inserted into PstI-BglII linearized Streptomyces vector pIJ702. The ligation mixture was then introduced into Streptomyces lividans TK54 protoplasts; transformants were identified based on their thiostrepton resistance (ThR) and insertional inactivation of the melanin phenotype; and three white colonies, XY-2, 6, and 9, harboring recombinant expression plasmid pYH703, were obtained. Enzyme assay and SDS-PAGE analysis indicated that the GI1 gene was expressed, the intracellular GI1 specific activity was 6 U/mg, and GI1 accounted for 20% of the soluble proteins in S. lividans. Restriction analysis and Southern blot of pYH703 showed the existence of plasmid deletion, presumably owing to the interaction between the mel and GI1 sequences. Continuous liquid cultures of the recombinant strain demonstrated that the GI1 specific activity and GI1 expression in S. lividans decreased, and more obviously under non-selective conditions.

Aldose-Ketose Isomerases↗
PubMed2000

Mechanism-based discovery of ligands that counteract inhibition of the nicotinic acetylcholine receptor by cocaine and MK-801.

Nicotinic acetylcholine receptors (AChR) belong to a family of proteins that form ligand-gated transmembrane ion channels. They are involved in the fast transmission of signals between cells and the control of intercellular communication in the nervous system. A variety of therapeutic agents and abused drugs, including cocaine, inhibit the AChR and monoamine transporters and interfere with nervous system function. Here we describe a mechanism-based approach to prevent this inhibition. We had previously developed presteady-state kinetic (transient kinetic) techniques, with microsecond-to-millisecond time resolutions, for investigations of reactions on cell surfaces that allow one to determine the effects of inhibitors not only on the channel-opening probability but also on the opening and closing rates of the AChR channel. The transient kinetic measurements led to two predictions. (i) Ligands that bind to a regulatory site on the closed-channel conformation of the AChR with higher affinity than to the site on the open-channel form shift the equilibrium toward the closed-channel form, thereby inhibiting the receptor. (ii) Ligands that bind to a regulatory site with an affinity for the open conformation equal to or higher than their affinity for the closed conformations are expected not to inhibit the receptor and to displace inhibitors. The identification of such ligands in a combinatorial library of RNA ligands is reported. The implication of this approach to other protein-mediated reactions in which an inhibitor changes the equilibrium between active and inactive conformations is discussed.

Animals↗
PubMed2000

High-affinity binding to the GM-CSF receptor requires intact N-glycosylation sites in the extracellular domain of the beta subunit.

The human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor consists of 2 glycoprotein subunits, GMRalpha and GMRbeta. GMRalpha in isolation binds to GM-CSF with low affinity. GMRbeta does not bind GM-CSF by itself, but forms a high-affinity receptor in association with GMRalpha. Previously, it was found that N-glycosylation of GMRalpha is essential for ligand binding. The present study investigated the role of N-glycosylation of the beta subunit on GM-CSF receptor function. GMRbeta has 3 potential N-glycosylation sites in the extracellular domain at Asn58, Asn191, and Asn346. Single mutants and triple mutants were constructed, converting asparagine in the target sites to aspartic acid or alanine. A single mutation at any of the 3 consensus N-glycosylation sites abolished high-affinity GM-CSF binding in transfected COS cells. Immunofluorescence and subcellular fractionation studies demonstrated that all of the GMRbeta mutants were faithfully expressed on the cell surface. Reduction of apparent molecular weight of the triple mutant proteins was consistent with loss of N-glycosylation. Intact N-glycosylation sites of GMRbeta in the extracellular domain are not required for cell surface targeting but are essential for high-affinity GM-CSF binding.

Alanine↗
PubMed2000

Rhodopsin kinase: two mAbs binding near the carboxyl terminus cause time-dependent inactivation.

Two mAbs generated against rhodopsin kinase (RK) were characterized for their epitopes. Both antibodies recognize short peptide sequences, overlapping but distinct, close to the carboxyl terminus. Binding of RK to the antibodies is slow. Attempts were made to use the antibodies immobilized on protein A-Sepharose beads to bind and purify the enzyme. Time-dependent inactivation of the enzyme occurred after its binding to the antibodies. Studies using different conditions to maintain the enzyme in the active form during binding or to reactivate the purified inactivated enzyme were unsuccessful.

Amino Acid Sequence↗
PubMed2000

Deletion of the Escherichia coli pseudouridine synthase gene truB blocks formation of pseudouridine 55 in tRNA in vivo, does not affect exponential growth, but confers a strong selective disadvantage in competition with wild-type cells.

Previous work from this laboratory (Nurse et al., RNA, 1995, 1:102-112) established that TruB, a pseudouridine (psi) synthase from Escherichia coli, was able to make psi55 in tRNA transcripts but not in transcripts of full-length or fragmented 16S or 23S ribosomal RNAs. By deletion of the truB gene, we now show that TruB is the only protein in E. coli able to make psi55 in vivo. Lack of TruB and psi55 did not affect the exponential growth rate but did confer a strong selective disadvantage on the mutant when it was competed against wild-type. The negative selection did not appear to be acting at either the exponential or stationary phase. Transformation with a plasmid vector conferring carbenicillin resistance and growth in carbenicillin markedly increased the selective disadvantage, as did growth at 42 degrees C, and both together were approximately additive such that three cycles of competitive growth sufficed to reduce the mutant strain to approximately 0.2% of its original value. The most striking finding was that all growth effects could be reversed by transformation with a plasmid carrying a truB gene coding for a D48C mutation in TruB. Direct analysis showed that this mutant did not make psi55 under the conditions of the competition experiment. Therefore, the growth defect due to the lack of TruB must be due to the lack of some other function of the protein, possibly an RNA chaperone activity, but not to the absence of psi55.

Amino Acid Sequence↗
PubMed2000

Growth regulation of human variant histone genes and acetylation of the encoded proteins.

The family of human histone genes consists of replication-dependent and independent subtypes. The replication-independent histone genes, also known as variants, give rise to distinct mRNAs, whose expression is regulated depending on the growth state of the cell, tissue type and developmental stage. In turn, the histone variants are differentially synthesized and modified by acetylation. Consequently, chromatin structure is altered resulting in complex changes in gene expression. The high conservation among histone protein subtypes suggests that they are indispensable. In addition, conservation of the positions of acetylation within subtypes suggests that the location of these sites is functionally important for the eukaryotic cell. For example, the structures of transcriptionally active and repressed chromatin are different depending on the acetylation state of histone proteins [1-3]. In addition, transcriptionally active and repressed chromatin contains distinct histone variants [4]. Specialized histone variants are targeted to the centromere of the chromosome, where they are essential for chromosome segregation [5]. Other specialized histones exist that are essential for development [6]. Changes in histone acetylation have been implicated in the down-regulation of a tumour suppressor gene in human breast cancer [7]. Acetylation also plays an important role in X chromosome inactivation as well as hormone-mediated transcriptional regulation [8, 9]. We propose here a novel model for histone variant gene regulation at the post-transcriptional level, which provides the groundwork to define the pathways regulating the synthesis of these variants.

Acetylation↗
PubMed2000

Structure of xylose isomerase from Streptomyces diastaticus no. 7 strain M1033 at 1.85 A resolution.

The structure of xylose isomerase (XyI) from Streptomyces diastaticus No. 7 strain M1033 (SDXyI) has been refined at 1.85 A resolution to conventional and free R factors of 0.166 and 0.219, respectively. SDXyI was crystallized in space group P2(1)2(1)2, with unit-cell parameters a = 87.976, b = 98.836, c = 93.927 A. One dimer of the tetrametric molecule is found in each asymmetric unit. Each monomer consists of two domains: a large N-terminal domain (residues 1-320), containing a parallel eight-stranded alpha/beta barrel, and a small C-terminal loop (residues 321-387), containing five helices linked by random coil. The four monomers are essentially identical in the tetramer, possessing non-crystallographic 222 symmetry with one twofold axis essentially coincident with the crystallographic twofold axis in the space group P2(1)2(1)2, which may explain why the diffraction pattern has strong pseudo-I222 symmetry even at medium resolution. The crystal structures of XyIs from different bacterial strains, especially from Streptomyces, are similar. The alpha2 helix of the alpha/beta barrel has a different position in the structures of different XyIs. The conformation of C-terminal fragment 357-364 in the SDXyI structure has a small number of differences to that of other XyIs. Two Co(2+) ions rather than Mg(2+) ions exist in the active site of the SDXyI structure; SDXyI seems to prefer to bind Co(2+) ions rather than Mg(2+) ions.

Aldose-Ketose Isomerases↗
PubMed2000

[Effect of unsymmetrical cutting along both river slopes on rainstorm-runoff process].

A simulation experiment was conducted to compare the effect of cutting and no-cutting at both slopes along a river on the rainstorm run-off in catchment, and a model was constructed. The results showed that the appearance of outflow and peak flow of surface run-off was later on forest slope than on forest-cutting slope. On forest slope, the duration was prolonged, and the peak flow and surface runoff were lower. These effects were more obvious as the slope gradient was bigger. When rain intensity was 1.98 mm.min-1 and rainfall was 108.8 mm, the peak flow and the total runoff on both forested slopes of gradient 15 degrees was 5% and 4% less than that on the cutting slopes, respectively.

Rain↗
PubMed1999

Kinetic resolution of two mechanisms for high-affinity granulocyte-macrophage colony-stimulating factor binding to its receptor.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important hematopoietic cytokine that exerts its effects by interaction with the GM-CSF receptor (GMR) on the surface of responsive cells. The GM-CSF receptor consists of two subunits: GMRalpha, which binds GM-CSF with low affinity, and GMRbeta, which lacks intrinsic ligand-binding capability but complexes with GMRalpha to form a high-affinity receptor (GMRalpha/beta). We conducted dynamic kinetic analyses of GM-CSF receptors to define the role of GMRbeta in the interaction of ligand and receptor. Our data show that GMRalpha/beta exhibits a higher k(on) than GMRalpha, indicating that GMRbeta facilitates ligand acquisition to the binding pocket. Heterogeneity with regard to GM-CSF dissociation from GMRalpha/beta points to the presence of loose and tight ligand-receptor complexes in high-affinity binding. Although the loose complex has a k(off) similar to GMRalpha, the lower k(off) indicates that GMRbeta inhibits GM-CSF release from the tight receptor complex. The two rates of ligand dissociation may provide for discrete mechanisms of interaction between GM-CSF and its high-affinity receptor. These results show that the beta subunit functions to stabilize ligand binding as well as to facilitate ligand acquisition.

Granulocyte-Macrophage Colony-Stimulating Factor↗
PubMed1999

Functional effect of deletion and mutation of the Escherichia coli ribosomal RNA and tRNA pseudouridine synthase RluA.

The Escherichia coli gene rluA, coding for the pseudouridine synthase RluA that forms 23 S rRNA pseudouridine 746 and tRNA pseudouridine 32, was deleted in strains MG1655 and BL21/DE3. The rluA deletion mutant failed to form either 23 S RNA pseudouridine 746 or tRNA pseudouridine 32. Replacement of rluA in trans on a rescue plasmid restored both pseudouridines. Therefore, RluA is the sole protein responsible for the in vivo formation of 23 S RNA pseudouridine 746 and tRNA pseudouridine 32. Plasmid rescue of both rluA- strains using an rluA gene carrying asparagine or threonine replacements for the highly conserved aspartate 64 demonstrated that neither mutant could form 23 S RNA pseudouridine 746 or tRNA pseudouridine 32 in vivo, showing that this conserved aspartate is essential for enzyme-catalyzed formation of both pseudouridines. In vitro assays using overexpressed wild-type and mutant synthases confirmed that only the wild-type protein was active despite the overexpression of wild-type and mutant synthases in approximately equal amounts. There was no difference in exponential growth rate between wild-type and MG1655(rluA-) either in rich or minimal medium at 24, 37, or 42 degrees C, but when both strains were grown together, a strong selection against the deletion strain was observed.

Electrophoresis, Polyacrylamide Gel↗
PubMed1999

Synthesis and photochemistry of a photolabile precursor of N-methyl-D-aspartate (NMDA) that is photolyzed in the microsecond time region and is suitable for chemical kinetic investigations of the NMDA receptor.

The amino acid L-glutamate is a major neurotransmitter at excitatory synapses within the central nervous system. Neuronal responses to glutamate are mediated by at least three receptor types, one of which is the NMDA subtype, named for its specific ligand N-methyl-D-aspartic acid. Neurotransmitter receptors are transmembrane proteins that can form ion channels upon binding a specific ligand and are involved in many physiological activities of the brain and in some neurological disorders. Elucidating the mechanisms of the formation of transmembrane receptor-channels and of receptor regulation and inhibition is necessary for understanding nervous system function and for designing potential therapeutic agents. This has been hampered by the lack of rapid reaction techniques suitable for investigating protein-mediated reactions on cell surfaces. Recently a laser-pulse photolysis technique was developed to study the chemical reactions of channel-forming receptor proteins in the microsecond-to-millisecond time region. To apply the technique to NMDA1 receptors a photolabile NMDA precursor (beta-DNB NMDA) was synthesized. In this precursor the side chain carboxylate was protected as a photosensitive 2,2'-dinitrobenzhydryl ester. Photolysis with 308 nm laser light generated free NMDA with a time constant of 4.2 +/- 0.1 microseconds at pH 7 and a photolysis quantum yield of 0.18 +/- 0.05. In rat hippocampal neurons the beta-DNB NMDA (250 microM) neither activated endogenously expressed receptors nor potentiated or inhibited the NMDA response. Equilibration of hippocampal neurons in the whole-cell current recording mode with 250 microM caged precursor followed by a pulse of 333 nm laser light resulted in a rapid current rise with a rate constant of 100 s-1 due to opening of NMDA-activated receptor-channels. The caged NMDA precursor described here now makes it possible to investigate the mechanism of NMDA receptors in the micro- to millisecond time region.

Animals↗
PubMed1999

Cloning and characterization of the 23S RNA pseudouridine 2633 synthase from Bacillus subtilis.

A Bacillus subtilis ORF, ypul, 41% homologous to rsuA, the gene for the synthase which forms pseudouridine 516 in Escherichia coli 16S rRNA, was cloned and the protein expressed and affinity-purified by the His tag procedure. Reactions with E. coli 16S and 23S rRNA transcripts were performed in vitro. The protein did not form pseudouridine 516 as expected but did produce pseudouridine 552 in 16S rRNA and pseudouridines 1199, 2605, and 2833 in 23S rRNA. Of these, only pseudouridine 2605 is found naturally in either E. coli or B. subtilis rRNA. Kinetic experiments confirmed that pseudouridine 2605 was the primary target. Comparison of the four pseudouridine sites yielded a consensus recognition sequence for the synthase. This consensus sequence was not present at any other site in either E. coli or B. subtilis 16S or 23S RNA. We propose that YpuL is the B. subtilis pseudouridine 2633 (2605 in E. coli) synthase. Since the closest gene sequence homologue in E. coli is yciL, we suggest that its gene product is the corresponding E. coli pseudouridine 2605 synthase.

Bacillus subtilis↗
PubMed1999

Detection of hydrazine, methylhydrazine and isoniazid by capillary electrophoresis with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode.

Capillary electrophoresis (CE)/electrochemical detection (EC) for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid has been developed with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode. Such an electrode has very high catalytic ability for hydrazines and they could be detected even at 0.0 V. The responses for hydrazine, methylhydrazine, and isoniazid are linear over 3 orders of detected concentration and of magnitude of 0.2-400 microM, 0.2-400 microM, 0.5 microM-2 mM, with correlation coefficients of 0.9998, 0.9991, and 0.9982, respectively. And they could be detected to levels of 0.1, 0.1 and 0.2 microM, respectively. This modified electrode was found to be very stable and reproducible when continuously used as detector for capillary electrophoresis for period of at least 4 weeks with no apparent loss of response.

Electrochemistry↗
PubMed1999

16S ribosomal RNA pseudouridine synthase RsuA of Escherichia coli: deletion, mutation of the conserved Asp102 residue, and sequence comparison among all other pseudouridine synthases.

The gene for RsuA, the pseudouridine synthase that converts U516 to pseudouridine in 16S ribosomal RNA of Escherichia coli, has been deleted in strains MG1655 and BL21/DE3. Deletion of this gene resulted in the specific loss of pseudouridine516 in both cell lines, and replacement of the gene in trans on a plasmid restored the pseudouridine. Therefore, rsuA is the only gene in E. coli with the ability to produce a protein capable of forming pseudouridine516. There was no effect on the growth rate of rsuA- MG1655 either in rich or minimal medium at either 24, 37, or 42 degrees C. Plasmid rescue of the BL21/DE3 rsuA- strain using pET15b containing an rsuA gene with aspartate102 replaced by asparagine or threonine demonstrated that neither mutant was active in vivo. This result supports a role for this aspartate, located in a unique GRLD sequence in this gene, at the catalytic center of the synthase. Induction of wild-type and the two mutant synthases in strain BL21/DE3 from genes in pET15b yielded a strong overexpression of all three proteins in approximately equal amounts showing that the mutations did not affect production of the protein in vivo and thus that the lack of activity was not due to a failure to produce a gene product. Aspartate102 is found in a conserved motif present in many pseudouridine synthases. The conservation and distribution of this motif in nature was assessed.

Amino Acid Sequence↗
PubMed1999

Structure of acutolysin-C, a haemorrhagic toxin from the venom of Agkistrodon acutus, providing further evidence for the mechanism of the pH-dependent proteolytic reaction of zinc metalloproteinases.

The structure of acutolysin-C, a haemorrhagic zinc metalloproteinase from the venom of Agkistrodon acutus, has been analyzed and refined at 2.2 A resolution. The space group of the crystal is P2(1)2(1)2(1), with unit-cell dimensions a = 46.84, b = 49.52, c = 95.34 A. One molecule was found in each asymmetric unit. The phasing problem was solved by the molecular-replacement program AMoRe. Crystallographic refinement was performed using X-PLOR, leading to final R and free R factors of 0.176 and 0.272, respectively. The residue sequence of acutolysin-C was determined mainly by electron density. No density was found for the first residue at the N--terminus and the last two residues at the C-terminus, which was also the case for most other P-I class snake-venom metalloproteinases (SVMPs). Acutolysin-C has two highly conserved characteristic sequences His142-Glu143-X-X-His146-X-X-Gly149-X-X-His15 2 and Cys162-Ile163-Met164. The enzyme has three disulfide bridges: Cys117-Cys195, Cys157-Cys179 and Cys159-Cys162. The entire structure shows good agreement with that of other reported P-I class SVMPs and has two subdomains with a cleft in which one catalytic zinc ion is localized. However, the local conformation (especially the disulfide configurations), the coordination of the catalytic water molecules and some residue side chains differ compared with other P-I class SVMPs. The proteolytic activities of SVMPs are sensitive to the pH value. The molecular superpositions around the proteolytic active sites of all the P-I class SVMP crystal structures show that the distances between the zinc ion and its ligands are not correlated with the crystallization pH values, although the contact distances between the catalytic water molecule and the O atoms of the Glu143 carboxylate group in the neutral and weakly alkaline structures are shorter than those in weakly acidic structures, and the closer the crystallization pH value of one enzyme is to its optimal activity pH value, the shorter the contact distances. Overall, all P-I class SVMPs have similar conformations in the active-site cleft. The size of the active site is not correlated with the crystallization pH values or the proteolytic activities. The disulfide bridge Cys117-Cys195 is conserved in all crystal structures of P-I class SVMPs, whereas the conformation and number of disulfide bridges in the C-terminal subdomain differ. Acutolysin-C has no structural calcium ion, which may not affect the proteolytic activity or haemorrhagic activity directly.

Agkistrodon↗
PubMed1999

[Ultrasonic and CT diagnosis of large upper abdominal mass].

OBJECTIVE: To assess accuracy of ultrasonic (US) and CT diagnosis of big mass in the upper abdomen. METHODS: Data from 38 clinically and pathologically confirmed cases were retrospectively analyzed and accuracy of their preoperative US and CT diagnosis compared. RESULTS: US diagnosis was correct in 3 of 9 (33.3%) cases with a mass in the liver, in 16 of 21 (76.2%) cases with a mass in the adrenal gland and in 2 of 4 cases with a mass in the kidney. In contrast, CT diagnosis was correct in 2 of 9 (22.2%) cases with a mass in the liver, in 4 of 18 (22.2%) cases with a mass in the adrenal gland and none in a case with a mass in the kidney. In 4 cases with a mass in the spleen, neither US nor CT diagnosis was correct. CONCLUSION: Because organs in the upper abdomen are closely located with each other, correct imaging localization of big mass in this region is not without difficulty. In this series, accuracy of diagnosis with US and CT is comparable, but for localizing tumor in the adrenal gland, US imaging seems superior. US and CT are both incapable of accurately diagnosing large mass in the spleen.

Abdominal Neoplasms↗