Search PubMed⌕ Search

Biomedical subjects

L Zhang

Publications and source records attributed to L Zhang.

At least 271 records · Page 15Linked to original sources
PubMed2001

A new phenomenon in the induction period of the methane dehydroaromatization reaction.

The induction period of dehydroaromatization of methane to benzene over Mo/HZSM-5 had been investigated in real-time by the resonant-enhanced two-photon ionization (RE2PI) technique; it is remarkable that there is a small amount of benzene formed in the early stage of the induction period; we suggest that the trace amount of benzene was caused by the reduction of the original Mo6+ ion during the induction period and the Mo6+ species has a slight catalytic activity for methane-benzene conversion.

Journal Article↗
PubMed2001

Effect of templated quenched disorder on fluid phase equilibrium.

Templating offers a means to direct the structure of quenched disorder. We show here that changes in phase equilibrium due to the presence of quenched disorder can themselves be altered by templating. We calculate the phase diagram of a fluid in a collection of template-directed, quenched particles by solving a set of replica Ornstein-Zernike equations within the mean spherical approximation and show templating to enhance phase behavior, that is, shift the phase envelope upward from its location for a nontemplated system of identical available volume. This enhancement is due to an augmented number of fluid-fluid interactions.

Journal Article↗
PubMed2001

DIgR1, a novel membrane receptor of the immunoglobulin gene superfamily, is preferentially expressed by antigen-presenting cells.

A novel membrane receptor of immunoglobulin gene superfamily (IgSF) has been identified from mouse dendritic cells (DC) and designated as DC-derived Ig-like receptor 1 (DIgR1). It encodes a 228-amino-acid (aa) residue polypeptide with a 21-aa signal peptide, a 20-aa transmembrane region, a 189-aa extracellular region, and a 19 aa intracellular region. Its extracellular region contains a single V domain of Ig. So it is a novel type I transmembrane glycoprotein of IgSF. DIgR1 shows significant homologies to human CMRF-35 antigens and polymeric immunoglobulin receptors (pIgR). The mRNA expression of DIgR1 was highly abundant in mouse spleen. The preferential expression of DIgR1 mRNA is observed in the known antigen-presenting cells (APC) including DC, monocytes/macrophages, and B lymphocytes. A 40 kDa of protein in NIH/3T3 cells transfected with the DIgR1 cDNA was detected by Western blot analysis using anti-DIgR1 polyclonal antibodies. The expression of DIgR1 protein on DC is not regulated by LPS stimulation. Further study should be conducted to investigate what were biological functions of DIgR1 in the immunobiology of APC.

Amino Acid Sequence↗
PubMed2001

6-O-sulfotransferase-1 represents a critical enzyme in the anticoagulant heparan sulfate biosynthetic pathway.

Using recombinant retroviral transduction, we have introduced the heparin/heparan sulfate (HS) 3-O-sulfotransferase 1 (3-OST-1) gene into Chinese hamster ovary (CHO) cells. Expression of 3-OST-1 confers upon CHO cells the ability to produce anticoagulantly active HS (HS(act)). To understand how 6-OST and other proteins regulate HS(act) biosynthesis, a CHO cell clone with three copies of 3-OST-1 was chemically mutagenized. Resulting mutants that make HS but are defective in generating HS(act) were single-cell-cloned. One cell mutant makes fewer 6-O-sulfated residues. Modification of HS chains from the mutant with pure 6-OST-1 and 3'-phosphoadenosine 5'-phosphosulfate increased HS(act) from 7% to 51%. Transfection of this mutant with 6-OST-1 created a CHO cell line that makes HS, 50% of which is HS(act). We discovered in this study that (i) 6-OST-1 is a limiting enzyme in the HS(act) biosynthetic pathway in vivo when the limiting nature of 3-OST-1 is removed; (ii) HS chains from the mutant cells serve as an excellent substrate for demonstrating that 6-OST-1 is the limiting factor for HS(act) generation in vitro; (iii) in contradiction to the literature, 6-OST-1 can add 6-O-sulfate to GlcNAc residues, especially the critical 6-O-sulfate in the antithrombin binding motif; (iv) both 3-O- and 6-O-sulfation can be the final step in HS(act) biosynthesis in contrast to prior publications that concluded 3-O-sulfation is the final step in HS(act) biosynthesis; (v), in the presence of HS interacting protein peptide, 3-O-sulfate-containing sugars can be degraded into disaccharides by heparitinase digestion as demonstrated by capillary high performance liquid chromatography coupled with mass spectrometry.

Animals↗
PubMed2001

Dynamic platelet accumulation at the site of the occluded middle cerebral artery and in downstream microvessels is associated with loss of microvascular integrity after embolic middle cerebral artery occlusion.

Information is lacking regarding dynamic platelet accumulation at the site of the occluded middle cerebral artery (MCA) and the relationship between platelet aggregation in downstream cerebral microvessels and loss of perfusion and vascular integrity of these microvessels. In the present study, we employed a model of embolic MCA occlusion in the rat to simultaneously measure temporal and spatial profiles of platelet accumulation at the site of the embolus occluding the MCA and within downstream cerebral microvessels. We also measured the integrity of microvessels and matrix metalloproteinase (MMP) activity in ischemic brain. Rats (n=36) were subjected to embolic MCA occlusion. Immunohistochemistry was used to detect microvascular integrity, plasminogen activator inhibitor 1 (PAI-1) and the deposition of fibrin. SDS-PAGE zymography was used to measure MMP2 and MMP9 activities. Accumulation of platelets and increases in PAI-1 immunoreactivity at the site of the embolus occluding the MCA were detected 1 h (n=7) and 4 h (n=7) after ischemia, respectively, and numbers of GPIIb/IIIa immunoreactive downstream cerebral microvessels increased significantly (209+/-59; n=7; P<0.05) 4 h after ischemia, suggesting dynamic platelet aggregation. A significant (n=7; P<0.01) diffuse loss of type IV collagen immunoreactivity in microvessels was temporally associated with platelet GPIIb/IIIa immunoreactivity within the vessels. Triple immunostaining revealed that microvessels containing platelet aggregates exhibited loss of type IV collagen immunoreactivity and both intra- and extra-vascular fibrin deposition, suggesting that intravascular platelet aggregation is associated with decreases in the integrity of the microvascular basal lamina and blood-brain barrier leakage. A significant increase (P<0.05) in MMP9 was detected at 4 h (n=3) and 24 h (n=3) after ischemia but levels of MMP2 were not significantly changed in ischemic brain. Our data suggest that dynamic platelet aggregation in ischemic brain may contribute to time-dependent resistance to fibrinolysis. In addition, platelet deposition and increased MMP9 coincided with degradation of type IV collagen and loss of vascular integrity. These data suggest an important role for post-occlusive distal platelet deposition in the pathophysiology of stroke.

Animals↗
PubMed2001

DNA-binding activity and subunit interaction of the mariner transposase.

Mos1 is a member of the mariner/Tc1 family of transposable elements originally identified in Drosophila mauritiana. It has 28 bp terminal inverted repeats and like other elements of this type it transposes by a cut and paste mechanism, inserts at TA dinucleotides and codes for a transposase. This is the only protein required for transposition in vitro. We have investigated the DNA binding properties of Mos1 transposase and the role of transposase-transposase interactions in transposition. Purified transposase recognises the terminal inverted repeats of Mos1 due to a DNA-binding domain in the N-terminal 120 amino acids. This requires a putative helix-turn-helix motif between residues 88 and 108. Binding is preferentially to the right hand end, which differs at four positions from the repeat at the left end. Cleavage of Mos1 by transposase is also preferentially at the right hand end. Wild-type transposase monomers interact with each other in a yeast two-hybrid assay and we have used this to isolate mutations resulting in reduced interaction. These mutations lie along the length of the protein, indicating that transposase-transposase interactions are not due to a single interaction domain. One such mutation which retains both DNA-binding and catalytic activity has greatly reduced ability to excise Mos1 from plasmid DNA through coordinate cleavage of the two ends and transposition in vitro is lowered to a level 20-fold below that of the wild-type. This suggests that transposase-transposase interaction is required to form a synaptic complex necessary for coordinate cleavage at the ends of Mos1 during transposition. This mutant enzyme allows insertion at dinucleotides other than TA, including sequences with GC base pairs. This is the first example of a mariner/Tc1 transposase with altered target specificity.

Amino Acid Sequence↗
PubMed2001

Evidence for droplet reorientation and interfacial charges in a polymer-dispersed liquid-crystal cell.

We observe a new feature ( plateau), sandwiched between two exponentially decaying components, in the switching response of a polymer-dispersed liquid-crystal (PDLC) cell. Upon application of square-wave electrical pulses, the cell response exhibits a complex decay whose characteristics are significantly different within and outside the applied field. We interpret these results in terms of reorientation dynamics of nonspherical droplets in the PDLC. Irradiation of the PDLC with gamma rays induces significant changes in the cell response in a manner that is consistent with redistribution of charges at the liquid-crystal-polymer interface in the PDLC.

Journal Article↗
PubMed2001

Ryanodine sensitizes the Ca(2+) release channel (ryanodine receptor) to Ca(2+) activation.

Ryanodine, a plant alkaloid, is one of the most widely used pharmacological probes for intracellular Ca(2+) signaling in a variety of muscle and non-muscle cells. Upon binding to the Ca(2+) release channel (ryanodine receptor), ryanodine causes two major changes in the channel: a reduction in single-channel conductance and a marked increase in open probability. The molecular mechanisms underlying these alterations are not well understood. In the present study, we investigated the gating behavior and Ca(2+) dependence of the wild type (wt) and a mutant cardiac ryanodine receptor (RyR2) after being modified by ryanodine. Single-channel studies revealed that the ryanodine-modified wt RyR2 channel was sensitive to inhibition by Mg(2+) and to activation by caffeine and ATP. In the presence of Mg(2+), the ryanodine-modified single wt RyR2 channel displayed a sigmoidal Ca(2+) dependence with an EC(50) value of 110 nm, whereas the ryanodine-unmodified single wt channel exhibited an EC(50) of 120 microm for Ca(2+) activation, indicating that ryanodine is able to increase the sensitivity of the wt RyR2 channel to Ca(2+) activation by approximately 1,000-fold. Furthermore, ryanodine is able to restore Ca(2+) activation and ligand response of the E3987A mutant RyR2 channel that has been shown to exhibit approximately 1,000-fold reduction in Ca(2+) sensitivity to activation. The E3987A mutation, however, affects neither [(3)H]ryanodine binding to, nor the stimulatory and inhibitory effects of ryanodine on, the RyR2 channel. These results demonstrate that ryanodine does not "lock" the RyR channel into an open state as generally believed; rather, it sensitizes dramatically the channel to activation by Ca(2+).

Alanine↗
PubMed2001

The nuclear localization signal of zebrafish terra is located within the DM domain.

Zebrafish Terra is a member of the DM domain-containing transcription factor family and is involved in somitogenesis. The other known members of this family play a role in sex differentiation across species from Caenorhabditis elegans to human. Using the green fluorescence protein-Terra fusion constructs, we have identified the nuclear localization signal (NLS) of terra by transfecting human HeLa cells. The terra NLS is located between the two intertwined zinc-binding sites of the DNA-binding domain. However, the nuclear translocation of terra is independent of the structure required for DNA binding. Mutational analysis demonstrates that basic residues K77 and R78 within the DM domain are absolutely required for the translocation of Terra into the nuclei. Sequence comparison discloses that the NLS of Terra is also present in the other known members of the DM family, indicating the conservative nature of the NLS of this family during evolution.

Amino Acid Sequence↗
PubMed2001

The cis-trans isomerization of 1,2,5,6-tetrasilacycloocta-3,7-dienes: analysis by mechanistic probes and density functional theory.

A series of alkyl- and aryl-substituted derivatives of cis,cis-1,2,5,6-tetrasilacycloocta-3,7-diene were prepared. Isomerization of these compounds to the corresponding trans,trans-1,2,5,6-tetrasilacycloocta-3,7-dienes by exposure to Ru and Zr hydride complexes was explored. Experimental probes of the isomerization were consistent with a stepwise mechanism involving metal hydride addition/elimination rather than one involving radical intermediates. Analysis of the low energy conformers of the various cis and trans isomers of 1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacycloocta-3,7-diene using density functional theory suggested the following trend in stability: trans,trans > cis,trans > cis,cis. The calculated trend in stability was consistent with the experimentally observed unidirectional isomerization of the carbon-carbon double bonds from all cis to all trans and supports a cis,trans isomer as a tenable intermediate.

Journal Article↗
PubMed2001

Kinetics of the cis,cis to trans,trans isomerization of 1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacycloocta-3,7-diene.

The kinetics of the ruthenium-promoted cis,cis to trans,trans isomerization of 1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacycloocta-3,7-diene were investigated. Incubation of a ruthenium alkylidene complex, (Cy(3)P)RuCl(2)(==CHPh)Ru(p-cymene)Cl(2), in CD(2)Cl(2) for 5 days at 40 degrees C afforded a catalytically active ruthenium species that was shown to be responsible for promoting the isomerization. The isomerization was observed to proceed in two steps: (1) conversion of the starting cis,cis isomer to a proposed cis,trans intermediate and (2) subsequent conversion of the intermediate to the product trans,trans isomer. Kinetic studies demonstrated that the two steps are first-order with respect to the concentrations of the cis,cis isomer, the intermediate, and the ruthenium alkylidene complex. The data were further consistent with a mechanism involving bimolecular hydride addition-elimination during the two isomerization steps.

Journal Article↗
PubMed2001

Evidence that Gal11 protein is a target of the Gal4 activation domain in the mediator.

The mediator is an approximately 20 protein complex that is essential for the transcription of most genes in yeast. It is contacted by a number of gene-specific activators, but the details of these interactions are not well understood in most cases. Here, evidence is presented that the mediator component Gal11 represents at least one target of the Gal4 activation domain (AD). Deletion of Gal11 is shown to decrease the affinity of the Gal4 AD for the mediator, and direct binding of an N-terminal domain of Gal11 with the Gal4 AD is demonstrated. Quantitative studies, however, indicate that the K(D) of the 1:1 Gal4 AD--Gal11 complex is modest. Combined with in vivo data showing that Delta gal11 cells exhibit reduced, but still significant, Gal4-mediated gene expression, these results suggest that the dimeric activator might also contact another protein in the mediator in addition to Gal11.

Binding, Competitive↗
PubMed2001

Clinical implications for affected parents and siblings of probands with long-QT syndrome.

BACKGROUND: Whenever a proband is identified with long-QT syndrome (LQTS), his or her parents and siblings should be evaluated regarding the possibility of carrying the disorder. In the majority of cases, one of the proband's parents and one or more siblings are affected. The aim of this study was (1) to determine whether the clinical severity of LQTS in the proband is useful in identifying first-degree family members at high risk for cardiac events, and (2) to evaluate the clinical course of affected parents and siblings of LQTS probands. METHODS AND RESULTS: The clinical and ECG characteristics of 211 LQTS probands and 791 first-degree relatives (422 parents and 369 siblings) were studied to determine if the clinical profile of the proband is useful in determining the clinical severity of LQTS in affected parents and siblings. Affected female parents of an LQTS proband had a greater cumulative risk for a first cardiac event than affected male parents. The probability of a parent or sibling having a first cardiac event was not significantly influenced by the severity of the proband's clinical symptoms. Female sex and QT(c) duration were risk factors for cardiac events among affected parents, and QT(c) was the only risk factor for cardiac events in affected siblings. CONCLUSIONS: The severity profile of LQTS in a proband was not found to be useful in identifying the clinical severity of LQTS in affected first-degree relatives of the proband.

Adolescent↗
PubMed2001

Characterization of the interaction between phospholipid and protein by capillary electrophoresis with laser-induced fluorescence detection.

We report an electrophoretic mobility shift-based method to study the interactions between phospholipids and proteins by capillary electrophoresis with laser-induced fluorescence detection. A fluorogenic dye, 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ), was used to label phosphatidylserine (PS). Then the FQ labeled PS (FQ-PS) was used as the fluorescent probe for monitoring the association between PS and bovine serum albumin (BSA). Two conjugates were observed to form between each PS species and BSA, indicating that two interactions exist between these PS species and BSA. We can also detect the competitive association with BSA between labeled PS and unlabeled PS. This method only needs a minute volume of sample. It is highly sensitive and can be used to detect the interaction between phospholipids and nanomolar concentrations of proteins, such as BSA.

Electrophoresis, Capillary↗
PubMed2001

Chromaffin cell F-actin disassembly and potentiation of catecholamine release in response to protein kinase C activation by phorbol esters is mediated through myristoylated alanine-rich C kinase substrate phosphorylation.

The large majority of chromaffin vesicles are excluded from the plasma membrane by a cortical F-actin network. Treatment of chromaffin cells with phorbol 12-myristate 13-acetate produces disassembly of cortical F-actin, increasing the number of vesicles at release sites (Vitale, M. L., Seward, E. P., and Trifaró, J. M. (1995) Neuron 14, 353-363). Here, we provide evidence for involvement of myristoylated alanine-rich protein kinase C substrate (MARCKS), a protein kinase C substrate, in chromaffin cell secretion. MARCKS binds and cross-links F-actin, the latter is inhibited by protein kinase C-induced MARCKS phosphorylation. MARCKS was found in chromaffin cells by immunoblotting. MARCKS was also detected by immunoprecipitation. In intact or permeabilized cells MARCKS phosphorylation increased upon stimulation with 10(-7) m phorbol 12-myristate 13-acetate. This was accompanied by cortical F-actin disassembly and potentiation of secretion. MARCKS phosphorylation, cortical F-actin disassembly, and potentiation of Ca(2+)-evoked secretion were inhibited by a peptide (MARCKS phosphorylation site domain sequence (MPSD)) with amino acid sequence corresponding to MARCKS phosphorylation site. MPSD was phosphorylated in the process. A similar peptide (alanine-substituted phosphorylated site domain) with four serine residues of MPSD substituted by alanines was ineffective. These results provide the first evidence for MARCKS involvement in chromaffin cell secretion and suggest that regulation of cortical F-actin cross-linking might be involved in this process.

Actins↗
PubMed2001

Interaction of cationic antimicrobial peptides with model membranes.

A series of natural and synthetic cationic antimicrobial peptides from various structural classes, including alpha-helical, beta-sheet, extended, and cyclic, were examined for their ability to interact with model membranes, assessing penetration of phospholipid monolayers and induction of lipid flip-flop, membrane leakiness, and peptide translocation across the bilayer of large unilamellar liposomes, at a range of peptide/lipid ratios. All peptides were able to penetrate into monolayers made with negatively charged phospholipids, but only two interacted weakly with neutral lipids. Peptide-mediated lipid flip-flop generally occurred at peptide concentrations that were 3- to 5-fold lower than those causing leakage of calcein across the membrane, regardless of peptide structure. With the exception of two alpha-helical peptides V681(n) and V25(p,) the extent of peptide-induced calcein release from large unilamellar liposomes was generally low at peptide/lipid molar ratios below 1:50. Peptide translocation across bilayers was found to be higher for the beta-sheet peptide polyphemusin, intermediate for alpha-helical peptides, and low for extended peptides. Overall, whereas all studied cationic antimicrobial peptides interacted with membranes, they were quite heterogeneous in their impact on these membranes.

Amino Acid Sequence↗
PubMed2001

A SecY homologue is involved in chloroplast-encoded D1 protein biogenesis.

We have used the photosystem II reaction center D1 protein as a model to study the mechanisms of targeting and insertion of chloroplast-encoded thylakoid membrane proteins. The unusually high turnover rate and distinct pausing intermediates during translation make the D1 protein biogenesis particularly suitable for these purposes. Here we show that cpSecY, a chloroplast homologue of bacterial essential translocon component SecY, interacts tightly with thylakoid membrane-bound ribosomes, suggesting its involvement in protein translocation and insertion. Co-immunoprecipitation and cross-linking experiments indicated that cpSecY resides in the vicinity of D1 elongation intermediates and provided evidence for a transient interaction of cpSecY with D1 elongation intermediates during the biogenesis of D1. After termination of translation, such interactions no longer existed. Our results indicate that, in addition to a well characterized role of cpSecY in posttranslational translocation of nuclear-encoded proteins, it seems to be also involved in cotranslational membrane protein translocation and insertion in chloroplasts.

Bacterial Proteins↗