Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 217 records · Page 12Linked to original sources

PubMed2001

Enhancement of the p300 HAT activity by HIV-1 Tat on chromatin DNA.

HIV-1 Tat is able to form a ternary complex with P/CAF and p300 and increase the affinity for CDK9/P-TEFb CTD kinase complex. Our previous study demonstrated that Tat binds to p300/CBP in the minimal HAT domain (aa 1253-1790) and that the interaction results in a change of conformation on p300/CBP. Here, we show that the Tat-p300 interaction increases the HAT activity of p300 on histone H4 that is associated with nucleosomal DNA and not with free histones. Nucleosomal histone H4 was acetylated on lysines 8, 12, and 16. Acetylation of H4 was inhibited by Lys-coenzyme A (CoA), a selective inhibitor of p300 acetyltransferase activity. Unexpectedly, we also found that Tat could autoacetylate itself, which was specific to lysine residues 41 and 71. Peptides lacking these two lysines could not enhance the HAT activity of p300. Comparison of the sequences of Tat with other HIV-1 clades and HAT containing transcription factors indicated sequence identity in the acetyl-CoA binding motif A, KGXG. Furthermore, when utilizing an in vitro transcription assay, as well as a Tat mutant virus, we found that ectopic expression of only wild-type Tat in the presence of p300, and not a lysine 41 Tat mutant, could activate HIV-1 chromatin DNA, as evidenced by the absence of HIV-1 virion antigen. Therefore, transcription of integrated viral DNA in vivo requires the HAT activity of coactivators that are modulated by Tat to derepress the HIV-1 chromatin structure and aid in activated transcription.

Acetyl-CoA C-Acetyltransferase↗

PubMed2001

Biradicals from benzoenyne-allenes. Application in the synthesis of 11H-benzo[b]fluoren-11-ols, 1H-cyclobut[a]indenes, and related compounds.

New synthetic pathways to 11H-benzo[b]fluoren-11-ols, 1H-cyclobut[a]indenes, and related compounds via biradicals generated from benzoenyne-allenes were developed. Treatment of the diacetylenic propargylic alcohols 13, derived from condensation between benzophenones and the lithium acetylide of 1-(2-ethynylphenyl)-2-phenylethyne, with thionyl chloride produced the 11-chloro-11H-benzo[b]fluorene 14 and, after hydrolysis, the corresponding 11H-benzo[b]fluoren-11-ols 15. The transformation involved a sequence of reactions, including a biradical-forming C2-C6 cyclization (Schmittel cyclization) reaction of the chlorinated benzoenyne-allene intermediates followed by an intramolecular radical-radical coupling to form the formal Diels-Alder adducts. Interestingly, in the case of the diacetylenic propargylic alcohol 26, obtained from dibenzosuberenone (25), an intramolecular [2 + 2] cycloaddition reaction of the chlorinated benzoenyne-allene intermediate occurred, furnishing the 1H-cyclobut[a]indene 27 exclusively. The dramatic change of the reaction pathway could be attributed to the emergence of a steric strain due to the nonbonded interactions with the chloro substituent along the pathway toward the formal Diels-Alder adduct 31. On the other hand, the non-chlorinated benzoenyne-allene, derived from prototropic isomerization of the diacetylenic hydrocarbon 60, underwent a formal Diels-Alder reaction to furnish the 11H-benzo[b]fluorene-type hydrocarbon 61 exclusively.

Journal Article↗

PubMed2001

A new route to hindered tertiary amines.

The Rh(2)(OAc)(4)-stabilized carbenoid derived from dimethyl diazomalonate has been found to insert into the N-H bond of sterically hindered secondary aliphatic amines to afford hindered tertiary aliphatic amines in quite satisfactory yields. For example dimethyl 2-(dicyclohexylamino)propanedioate was formed in 85% yield from dicyclohexylamine, and the severely hindered dimethyl 2-(2,2,6,6-tetramethyl-1-piperidinyl)propanedioate was formed in 38% yield from 2,2,6,6-tetramethylpiperidine. The Rh(2)(OAc)(4) - dimethyl diazomalonate reaction was found to work also for arylalkylamines and diarylamines. In these cases, small amounts of products resulting from formal insertion of the carbenoid into an aromatic C-H bond were detected. Substitution at ortho positions caused the yield of C-H insertion products to increase. Other diazo compounds, viz. ethyl diazoacetoacetate, 2-diazocyclohexane-1,3-dione, and 2-diazo-5,5-dimethylcyclohexane-1,3-dione, performed satisfactorily in Rh(2)(OAc)(4)-catalyzed reactions with arylalkylamines and diarylamines, but led to complicated reaction mixtures with dialkylamines.

Journal Article↗

PubMed2001

Structural basis for pterin antagonism in nitric-oxide synthase. Development of novel 4-oxo-pteridine antagonists of (6R)-5,6,7,8-tetrahydrobiopterin.

Pathological nitric oxide (NO) generation in sepsis, inflammation, and stroke may be therapeutically controlled by inhibiting NO synthases (NOS). Here we targeted the (6R)-5,6,7,8-tetrahydro-l-biopterin (H(4)Bip)-binding site of NOS, which, upon cofactor binding, maximally increases enzyme activity and NO production from substrate l-arginine. The first generation of H(4)Bip-based NOS inhibitors employed a 4-amino pharmacophore of H(4)Bip analogous to antifolates such as methotrexate. We developed a novel series of 4-oxo-pteridine derivatives that were screened for inhibition against neuronal NOS (NOS-I) and a structure-activity relationship was determined. To understand the structural basis for pterin antagonism, selected derivatives were docked into the NOS pterin binding cavity. Using a reduced 4-oxo-pteridine scaffold, derivatives with certain modifications such as electron-rich aromatic phenyl or benzoyl groups at the 5- and 6-positions, were discovered to markedly inhibit NOS-I, possibly due to hydrophobic and electrostatic interactions with Phe(462) and Ser(104), respectively, within the pterin binding pocket. One of the most effective 4-oxo compounds and, for comparisons an active 4-amino derivative, were then co-crystallized with the endothelial NOS (NOS-III) oxygenase domain and this structure solved to confirm the hypothetical binding modes. Collectively, these findings suggest (i) that, unlike the antifolate principle, the 4-amino substituent is not essential for developing pterin-based NOS inhibitors and (ii), provide a steric and electrostatic basis for their rational design.

Animals↗

PubMed2001

Direct measurements of the enthalpy of solution of solid solute in supercritical fluids: study on the CO2-naphthalene system.

A setup for a calorimeter for simultaneously measuring the solubility and the solution enthalpy of solid solutes in supercritical fluids (SCFs) has been established. The enthalpy of solution of naphthalene in supercritical CO2 was measured at 308.15 K in the pressure range from 8.0-11.0 MPa. It was found that the enthalpy of solution (deltaH) was negative in the pressure range from 8.0 to 9.5 MPa, and the absolute value decreased with increasing pressure. In this pressure range, the dissolution of the solute was enthalpy driven. However, the deltaH became positive at pressures higher than 9.5 MPa, and the dissolution was entropy driven. Monte Carlo simulation was performed to analyze the local structural environment of the solvated naphthalene molecules in supercritical CO2 under the experimental conditions for the calorimetric measurements. By combining the enthalpy data and the simulation results, it can be deduced that the energy level of CO2 in the high compressible region is higher than that at higher pressures, which results in the large negative enthalpy of solution and the larger degree of solvent-solute clustering in the high compressible region.

Journal Article↗

PubMed2001

Retinoblastoma protein interacts with ATF2 and JNK/p38 in stimulating the transforming growth factor-beta2 promoter.

Two highly related transcription factors, ATF2 and ATFa, enhance the activity of the Transforming Growth Factor beta2 (TGF-beta2) promoter via a partial cAMP response element in transfected CHO cells. The retinoblastoma protein (Rb) also activates this promoter and enhances the stimulatory effects of ATF2 but causes near extinction of the effects of ATFa. The site on Rb required for its effects alone and in combination with the ATFs has been mapped mainly to the A/B pockets but the C pocket is also implicated. Whereas MKK7 or JNK expression enhances the actions of both ATFs, MKK6 or p38 expression only augments the effects of ATF2. Immunoprecipitation with Rb antibodies of lysates from transfected cells brings down expressed ATF2 but not ATFa. Expressed JNK and p38 are also found in the anti-Rb immunoprecipitates. ATF2 antibodies bring down expressed Rb, JNK and p38 and expression of Rb enhances the immunoprecipitation of both JNK and p38 by ATF2 antibodies. The results suggest that Rb is acting as a matchmaker by bridging either JNK or p38 with their common substrate ATF2 and, hence, facilitating its activation. Consistent with this suggestion, expression of Rb enhances the phosphorylation of ATF2 in CHO cells.

Activating Transcription Factor 2↗

PubMed2001

Spatial control of cellular measurements with the laser micropipet.

Continued progress in understanding cellular physiology requires new strategies for biochemical measurements in solitary cells, multiple cells, and subcompartments of cells. Large spatial gradients in the concentrations of molecules and presumably the activities of enzymes can occur in cells. Consequently, there is a critical need for measurement techniques for mammalian cells with control over the numbers or regions of cells interrogated. In the present work, we developed a strategy to rapidly load the cytoplasmic contents of either multiple cells or a subregion of a single cell into a capillary. A single, focused pulse from a laser created a mechanical shock wave which disrupted a group of cells or a portion of a cell in the path of the shock wave. Simultaneously, the cytoplasm was loaded into a capillary for electrophoretic separation. The size of the region of cellular disruption (and therefore the volume of cytoplasm collected) was controlled by the amount of energy in the laser pulse. Higher energies could be used to sample groups of cells while much lower energies could be utilized to selectively sample the tip of a neuronal process. The feasibility of performing measurements on subcellular compartments was also demonstrated by targeting reporter molecules to these compartments. A reporter localized to the nucleus was detected on the electropherogram following laser-mediated disruption of the cell and the nucleus. Finally, we demonstrate that this method terminated cellular reactions with sufficient rapidity that cellular membrane repair mechanisms were not activated during cytoplasmic collection. The combined ability to preselect a spatial region of a cell or cells and to rapidly load that region into a capillary will greatly enhance the utility of CE in the biochemical analysis of cells.

Amino Acid Sequence↗

PubMed2001

Thermoregulated expression of virulence factors in plant-associated bacteria.

Pathogenic bacteria with habitats inside and outside a given host react to changes in environmental parameters by synthesizing gene products specifically needed during pathogenic or saprophytic growth. Temperature effects have been investigated in detail for pathogens of warm-blooded hosts, and major principles governing the temperature-sensing mechanism have been uncovered. Generally, transcription of virulence genes in these pathogens is induced at higher temperatures (37-41 degrees C), which are typical for body cavities and host tissues. However, effects of temperature on virulence determinants in plant pathogenic bacteria have not been focused on in detail. Interestingly, almost all virulence genes of plant pathogenic bacteria studied with respect to temperature exhibit increased transcription at temperatures well below the respective growth optima. This includes virulence determinants such as those directing bacteria-to-plant gene transfer, plant cell-wall-degrading enzymes, phytotoxins, ice nucleation activity, exopolysaccharide production, and the type III protein secretion machinery. Although many of the studied phytopathogens cause "cold-weather" diseases, the ecological rationale for this phenomenon remains to be studied in detail. This mini-review summarizes our current knowledge on thermoregulation of cellular processes taking place in bacterial phytopathogens in response to temperature changes. Since the temperature range of interest is different from that relevant to pathogens of mammals, one envisions novel principles of thermo-sensing in bacteria interacting with plants.

Bacteria↗

PubMed2001

Protein kinase C gamma-like immunoreactivity of trigeminothalamic neurons in the medullary dorsal horn of the rat.

We examined protein kinase C gamma-like immunoreactivity (PKCgamma-LI) of trigeminothalamic neurons in the rat medullary dorsal horn (MDH) after injecting a retrograde tracer, Fluoro-Gold (FG), into the thalamus. Over 90% of FG-labeled neurons in the marginal layer (lamina I) and a few FG-labeled neurons in the superficial part of the magnocellular layer (lamina III) showed PKCgamma-LI. No PKCgamma-neurons in the substantia gelatinosa (lamina II) were labeled with FG. PKCgamma-mediated regulation of trigeminothalamic neurons may contribute to the changes in MDH activity during persistent pain.

Animals↗

PubMed2001

Induction of cytokine mRNA in peripheral blood mononuclear cells of infants after the first dose of measles vaccine.

To better characterize the cytokine response to measles virus vaccine, we examined the levels of IL-2, IL-4, IL-5, IL-10, IL-12 and gamma-interferon (gamma-IFN) in measles virus-stimulated peripheral blood mononuclear cells from 18 donors before and 2 weeks after vaccination. Donors were grouped as seropositive or seronegative on the basis of measles-specific IgM antibody present at 2 weeks postvaccination. After vaccination, similar levels of upregulation of IL-2 and gamma-IFN mRNA were observed in the two groups. The majority of donors in both groups did not exhibit an increase in measles specific IL-4 or IL-10 mRNA after vaccination. IL-12 mRNA was not induced by measles virus in any of the donors. A statistically significant upregulation of IL-5 mRNA was observed among seropositive (9/13) compared with seronegative (1/5) donors after vaccination (P=0.09, one tailed Fisher's test). The observed measles specific induction of IL-5 mRNA is suggestive of a possible association between IL-5 production and an antibody response to measles virus.

Antibodies, Viral↗

PubMed2001

Li2AlB5O10.

A new compound, dilithium aluminium pentaborate, Li(2)AlB(5)O(10), has been synthesized by solid-state reaction and its structure determined by single-crystal X-ray diffraction. This compound is composed of [B(5)O(10)](5-) groups linked by AlO(4) tetrahedra. The [B(5)O(10)](5-) group consists of two hexagonal B-O rings perpendicular to each other connected by tetracoordinated boron. All the B-O rings in this structure can be divided into two groups, with one group approximately parallel and the other perpendicular to the c axis.

Journal Article↗

PubMed2001

Synthesis of a divalent glycoside of an alpha-galactosyl disaccharide epitope involved in the hyperacute rejection of xenotransplantation.

3,6-dioxaoct-1,8-diyl di-(3-O-alpha-D-galactopyranosyl-beta-D-galactopyranoside) was synthesized for use in research on hyperacute rejection of xenotransplantation. The trichloroacetate method was successfully applied to form stereoselectively the alpha-D-galactosyl linkage under mild reaction conditions and a simple procedure. The divalent O-glycoside was formed from the corresponding trichloroacetimidate in one step with reasonable yield.

Carbohydrate Sequence↗

PubMed2001

Assembly of metal-organic frameworks from large organic and inorganic secondary building units: new examples and simplifying principles for complex structures.

The secondary building unit (SBU) has been identified as a useful tool in the analysis of complex metal-organic frameworks (MOFs). We illustrate its applicability to rationalizing MOF crystal structures by analysis of nine new MOFs which have been characterized by single-crystal X-ray diffraction. Tetrahedral SBUs in Zn(ADC)(2).(HTEA)(2) (MOF-31), Cd(ATC).[Cd(H(2)O)(6)](H2O)(5) (MOF-32), and Zn(2)(ATB)(H2O).(H2O)(3)(DMF)(3) (MOF-33) are linked into diamond networks, while those of Ni(2)(ATC)(H(2)O)(4).(H2O)(4) (MOF-34) have the structure of the Al network in SrAl(2). Frameworks constructed from less symmetric tetrahedral SBUs have the Ga network of CaGa(2)O(4) as illustrated by Zn(2)(ATC).(C(2)H(5)OH)(2)(H2O)(2) (MOF-35) structure. Squares and tetrahedral SBUs in Zn(2)(MTB)(H2O)(2).(DMF)(6)(H2O)(5) (MOF-36) are linked into the PtS network, which is the simplest structure type known for the assembly of these shapes. The octahedral SBUs found in Zn(2)(NDC)(3).[(HTEA)(DEF)(ClBz)](2) (MOF-37) form the most common structure for linking octahedral shapes, namely, the boron network in CaB(6). New structure types for linking triangular and trigonal prismatic SBUs are found in Zn(3)O(BTC)(2).(HTEA)(2) (MOF-38) and Zn(3)O(HBTB)(2)(H2O).(DMF)(0.5)(H2O)(3) (MOF-39). The synthesis, crystal structure, and structure analysis using the SBU approach are presented for each MOF.

Journal Article↗

PubMed2001

Multiple conformations of PEVK proteins detected by single-molecule techniques.

An important component of muscle elasticity is the PEVK region of titin, so named because of the preponderance of these amino acids. However, the PEVK region, similar to other elastomeric proteins, is thought to form a random coil and therefore its structure cannot be determined by standard techniques. Here we combine single-molecule electron microscopy and atomic force microscopy to examine the conformations of the human cardiac titin PEVK region. In contrast to a simple random coil, we have found that cardiac PEVK shows a wide range of elastic conformations with end-to-end distances ranging from 9 to 24 nm and persistence lengths from 0.4 to 2.5 nm. Individual PEVK molecules retained their distinctive elastic conformations through many stretch-relaxation cycles, consistent with the view that these PEVK conformers cannot be interconverted by force. The multiple elastic conformations of cardiac PEVK may result from varying degrees of proline isomerization. The single-molecule techniques demonstrated here may help elucidate the conformation of other proteins that lack a well-defined structure.

Connectin↗

PubMed2001

The Ising model in physics and statistical genetics.

Interdisciplinary communication is becoming a crucial component of the present scientific environment. Theoretical models developed in diverse disciplines often may be successfully employed in solving seemingly unrelated problems that can be reduced to similar mathematical formulation. The Ising model has been proposed in statistical physics as a simplified model for analysis of magnetic interactions and structures of ferromagnetic substances. Here, we present an application of the one-dimensional, linear Ising model to affected-sib-pair (ASP) analysis in genetics. By analyzing simulated genetics data, we show that the simplified Ising model with only nearest-neighbor interactions between genetic markers has statistical properties comparable to much more complex algorithms from genetics analysis, such as those implemented in the Allegro and Mapmaker-Sibs programs. We also adapt the model to include epistatic interactions and to demonstrate its usefulness in detecting modifier loci with weak individual genetic contributions. A reanalysis of data on type 1 diabetes detects several susceptibility loci not previously found by other methods of analysis.

Algorithms↗

PubMed2001

Treatment of spinal muscular atrophy by sodium butyrate.

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by degeneration of the anterior horn cells of the spinal cord, leading to muscular paralysis with muscular atrophy. No effective treatment of this disorder is presently available. Studies of the correlation between disease severity and the amount of survival motor neuron (SMN) protein have shown an inverse relationship. We report that sodium butyrate effectively increases the amount of exon 7-containing SMN protein in SMA lymphoid cell lines by changing the alternative splicing pattern of exon 7 in the SMN2 gene. In vivo, sodium butyrate treatment of SMA-like mice resulted in increased expression of SMN protein in motor neurons of the spinal cord and resulted in significant improvement of SMA clinical symptoms. Oral administration of sodium butyrate to intercrosses of heterozygous pregnant knockout-transgenic SMA-like mice decreased the birth rate of severe types of SMA-like mice, and SMA symptoms were ameliorated for all three types of SMA-like mice. These results suggest that sodium butyrate may be an effective drug for the treatment of human SMA patients.

Abnormalities, Multiple↗

PubMed2001

Di-mu-phenylthio-bis[bis(eta5-methyl-cyclopentadienyl)(tetrahydrofuran)-lanthanum(III)] bis(tetrahydrofuran) solvate.

The title complex, [La(2)(C(6)H(7))(4)(C(6)H(5)S)(2)(C(4)H(8)O)(2)].2C(4)H(8)O, is a centrosymmetric dimer bridged through the S atoms of the benzenethiolate ligands. The bridging La(2)S(2) unit is completely planar, while the geometry around the nine-coordinate La atom is that of a distorted trigonal bipyramid. The La-S-La and S-La-S angles are 117.51 (4) and 62.5 (1) degrees, respectively, and the average La-S bond length is 2.9759 A. The crystals contain two tetrahydrofuran solvate molecules for every complex molecule.

Journal Article↗

PubMed2001

Modifications of cysteine residues in the solution and membrane-associated conformations of phosphatidylinositol transfer protein have differential effects on lipid transfer activity.

The alpha isoforms of mammalian phosphatidylinositol transfer protein (PITP) contain four conserved Cys residues. In this investigation, a series of thiol-modifying reagents, both alkylating and mixed disulfide-forming, was employed to define the accessibility of these residues and to evaluate their role in protein-mediated intermembrane phospholipid transport. Isolation and analysis of chemically modified peptides and site-directed mutagenesis of each Cys residue to Ala were also performed. Soluble, membrane-associated, and denatured preparations of wild-type and mutant rat PITPs were studied. Under denaturing conditions, all four Cys residues could be detected spectrophotometrically by chemical reaction with 4,4'-dipyridyl disulfide or 5,5'-dithiobis(2-nitrobenzoate). In the native protein, two of the four Cys residues were sensitive to some but not all thiol-modifying reagents, with discrimination based on the charge and hydrophobicity of the reagent and the conformation of the protein. With the soluble conformation of PITP, achieved in the absence of phospholipid vesicles, the surface-exposed Cys(188) was chemically modified without consequence to lipid transfer activity. Cys(188) exhibited an apparent pK(a) of 7.6. The buried Cys(95), which constitutes part of the phospholipid substrate binding site, was covalently modified upon transient association of PITP with a membrane surface. The Cys-to-Ala mutations showed that neither Cys(95) nor Cys(188) was essential for lipid transfer activity. However, chemical modification of Cys(95) resulted in the loss of lipid transfer activity. These results demonstrate that the Cys residues of PITP can be assigned to several different classes of chemical reactivity. Of particular interest is Cys(95), whose sulfhydryl group becomes exposed to modification in the membrane-associated conformation of PITP. Furthermore, the inhibition of PITP activity by thiol-modifying reagents is a result of steric hindrance of phospholipid substrate binding.

Animals↗