Allele frequencies of mitochondrial DNA STR locus in two Chinese ethnic groups.
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China↗
Biomedical subjects
H Tang
Publications and source records attributed to H Tang.
Evidence for the existence of an unfolding intermediate of thyroglobulin during denaturation by guanidine hydrochloride.
The unfolding of bovine thyroglobulin (Tg) in guanidine hydrochloride (GuHCl) solution was studied by following the fluorescence and circular dichroism. With increasing GuHCl concentrations, the emission maximum of the intrinsic fluorescence clearly red-shifted in two stages. At concentrations of GuHCl less than 1.2 M or more than 1.6 M, the red shift showed a cooperative manner. At concentrations of GuHCl between 1.2 and 1.6 M, an unfolding intermediate was observed. It was further characterized by the increased binding of the fluorescence probe 1-anilinonaphthalene-8-sulfonic acid (ANS). No significant changes of the secondary structure were indicated by CD spectra at the concentrations of GuHCl between 1.2 and 1.6 M. The conformation of this state has properties similar to those of a molten globule state which may exist in the folding pathway of the protein. Further changes in fluorescence properties occurred at concentrations of denaturant higher than 1.6 M with a significant red shift of the emission maximum from 340 to 347 nm and a marked decrease in ANS binding. This in vitro study gave a clue to understand the biochemical mechanism for the occurrence of aggregation and molecular chaperone binding during Tg maturation in vivo.
Anilino Naphthalenesulfonates↗
Crystallization and preliminary X-ray crystallographic studies of a macromolecular antitumour antibiotic, C1027.
C1027 is a macromolecular antitumour antibiotic produced by Streptomyces globispourus C1027 and consists of an apoprotein and a non-protein labile chromophore. Little is known about how the thermally unstable chromophore is stabilized by the apoprotein. The purified C1027 was monodisperse according to dynamic light-scattering measurements and crystallized in two different crystal forms from two different starting conditions using the vapour-diffusion method. Condition I yielded hexagonal prism crystals having space group P3(1)/P3(2) and unit-cell parameters a = b = 66.8, c = 55.4 A. Diffraction data were collected to 2.1 A resolution using an in-house Rigaku rotating Cu anode X-ray generator. Another condition produced rod-like crystals with space group P3(1)21/P3(2)21 and unit-cell parameters a = b = 55.15, c = 55.87 A. A data set to 1.8 A resolution was collected from a rod-like crystal using a MAR CCD detector at the SRS synchrotron source.
Aminoglycosides↗
Proteins of the cyanobacterial photosystem I.
Cyanobacterial photosystem (PS) I is remarkably similar to its counterpart in the chloroplast of plants and algae. Therefore, it has served as a prototype for the type I reaction centers of photosynthesis. Cyanobacterial PS I contains 11-12 proteins. Some of the cyanobacterial proteins are modified post-translationally. Reverse genetics has been used to generate subunit-deficient cyanobacterial mutants, phenotypes of which have revealed the functions of the missing proteins. The cyanobacterial PS I proteins bind cofactors, provide docking sites for electron transfer proteins, participate in tertiary and quaternary organization of the complex and protect the electron transfer centers. Many of these mutants are now being used in sophisticated structure-function analyses. Yet, the roles of some proteins of the cyanobacterial PS I are unknown. It is necessary to examine functions of these proteins on a global scale of cell physiology, biogenesis and evolution.
Cyanobacteria↗
Transcription and replication of a natural hepatitis B virus nucleocapsid promoter variant is regulated in vivo by peroxisome proliferators.
A hepatitis B virus (HBV) transgenic mouse containing a naturally occurring mutation in the nucleocapsid promoter (A1764T plus G1766A) that inhibits the retinoid X receptor alpha (RXRalpha) plus peroxisome proliferator-activated receptor alpha (PPARalpha) heterodimer from binding to the proximal nuclear hormone receptor recognition sequence has been generated. Viral transcription and replication occur in the liver and kidney. The nucleocapsid promoter mutation does not prevent peroxisome proliferators from increasing viral transcription and replication in the liver of these variant HBV transgenic mice. This suggests that peroxisome proliferators may enhance viral transcription directly in a PPARalpha-dependent manner through the nuclear hormone receptor recognition site in the enhancer 1 region of the HBV genome. Hepatocyte nuclear factor 4 (HNF4) binding to the proximal nuclear hormone receptor recognition sequence in the nucleocapsid promoter appears to limit RNA synthesis from the precore transcription initiation site. Consequently, the variant HBV transgenic mice transcribe very little precore RNA and secrete extremely low levels of hepatitis B e antigen (HBeAg) compared with the wild-type HBV transgenic mice. This is consistent with the suggestion that viruses expressing HBeAg are preferentially eliminated in infected individuals when they seroconvert from HBeAg positive to anti-HBe antibody-positive status, leaving escape HBV variants that have reduced HBeAg expression.
3T3 Cells↗
Crystallization and preliminary X-ray analysis of a Trx domain of human thioredoxin-like protein.
The Trx domain of human thioredoxin-like protein has been purified and crystallized using ammonium sulfate as precipitant. The crystal belongs to space group C2, with unit-cell parameters a = 87.5, b = 48.5, c = 29.8 A, beta = 99.59 degrees. It has one molecule per asymmetric unit and diffracts beyond 2.2 A under cryoconditions (100 K) using an in-house Cu rotating-anode X-ray generator.
Crystallization↗
Crystallization and preliminary X-ray crystallographic analysis of native and selenomethionyl recombinant tabtoxin-resistance protein complexed with acetyl-coenzyme A.
Tabtoxin-resistance protein (TTR), an acetyltransferase from Pseudomonas syringae pv. tabaci, was overexpressed in Eschericha coli M15 and the TTR fusion protein complexed with acetyl-coenzyme A (AcCoA) was purified and crystallized. Diffraction data were collected to 3.0 A resolution in-house and the crystal was found to belong to space group P2(1), with unit-cell parameters a = 47.6, b = 66.6, c = 53.5 A, beta = 104.3 degrees. Furthermore, a selenomethionine (SeMet) TTR fusion protein derivative was overexpressed in the same expression system and its complex with AcCoA was purified in a reductive environment. The SeMet TTR derivative crystallized in two forms: the first was identical to that observed for native crystals and the second belonged to space group C2, with unit-cell parameters a = 101.7, b = 45.6, c = 84.2 A, beta = 105.8 degrees. Data from the P2(1) crystal form were collected in-house to 2.3 A resolution. Subsequently, three different wavelength data sets of the C2 crystal form to 1.55 A resolution were collected at the Advanced Photon Source at Argonne National Laboratory.
Acetyl Coenzyme A↗
Signal transduction in neuronal migration: roles of GTPase activating proteins and the small GTPase Cdc42 in the Slit-Robo pathway.
The Slit protein guides neuronal and leukocyte migration through the transmembrane receptor Roundabout (Robo). We report here that the intracellular domain of Robo interacts with a novel family of Rho GTPase activating proteins (GAPs). Two of the Slit-Robo GAPs (srGAPs) are expressed in regions responsive to Slit. Slit increased srGAP1-Robo1 interaction and inactivated Cdc42. A dominant negative srGAP1 blocked Slit inactivation of Cdc42 and Slit repulsion of migratory cells from the anterior subventricular zone (SVZa) of the forebrain. A constitutively active Cdc42 blocked the repulsive effect of Slit. These results have demonstrated important roles for GAPs and Cdc42 in neuronal migration. We propose a signal transduction pathway from the extracellular guidance cue to intracellular actin polymerization.
Actins↗
Introduction to Maxxam all-season passive sampling system and principles of proper use of passive samplers in the field study.
Maxxam all-season passive sampling system (PASS) is introduced in this paper. The PASS can be used to quantitatively and accurately monitor SO2, NO2, O3, and H2S in air in all weather conditions with flexible exposure times from several hours to several months. The air pollution detection limits of PASS are very low. They can be from sub ppb to ppt levels. The principles of proper use of passive samplers in the field study are discussed by using the PASS as an example.
Air Pollutants↗
Electrochemical properties of self-assembled monolayers of tripod-shaped molecules and their applications to organic light-emitting diodes.
Self-assembled monolayers of a tripod-shaped conjugated-thiol grafted onot Au(111) substrates are found to show electrochemically reversible oxidation and reduction and to improve electroluminescence performances of organic light-emitting diodes.
Journal Article↗
An Eulerian path approach to DNA fragment assembly.
For the last 20 years, fragment assembly in DNA sequencing followed the "overlap-layout-consensus" paradigm that is used in all currently available assembly tools. Although this approach proved useful in assembling clones, it faces difficulties in genomic shotgun assembly. We abandon the classical "overlap-layout-consensus" approach in favor of a new euler algorithm that, for the first time, resolves the 20-year-old "repeat problem" in fragment assembly. Our main result is the reduction of the fragment assembly to a variation of the classical Eulerian path problem that allows one to generate accurate solutions of large-scale sequencing problems. euler, in contrast to the celera assembler, does not mask such repeats but uses them instead as a powerful fragment assembly tool.
Algorithms↗
Recording intramolecular mechanics during the manipulation of a large molecule.
The technique of single atom manipulation by means of the scanning tunneling microscope (STM) applies to the controlled displacement of large molecules. By a combined experimental and theoretical work, we show that in a constant height mode of manipulation the STM current intensity carries detailed information on the internal mechanics of the molecule when guided by the STM tip. Controlling and time following the intramolecular behavior of a large molecule on a surface is the first step towards the design of molecular tunnel-wired nanorobots.
Journal Article↗
Mapping the functional domains of HAP95, a protein that binds RNA helicase A and activates the constitutive transport element of type D retroviruses.
The complex retroviruses such as human immunodeficiency virus, type 1, employ a virally encoded protein, Rev, to mediate the nuclear export of unspliced and partially spliced mRNA. In contrast, the simian type D retroviruses act through a cis-acting constitutive transport element (CTE) that presumably interacts directly with cellular export proteins. We first reported that RNA helicase A (RHA) is a shuttle protein that binds to functional CTE in vitro and in vivo. Recently, we isolated a novel protein, HAP95, that specifically binds to the nuclear transport domain of RHA and up-regulates CTE-mediated gene expression. Here, using truncation and deletion mutations, we mapped the domains of HAP95 that are important for RHA binding, transactivation of CTE, and nuclear cytoplasmic shuttling. We report evidence for a novel nuclear export signal in HAP95 and showed that the domains involved in RHA binding and nuclear localization are required for CTE activation. Finally, we showed that HAP95 synergizes significantly with RHA on CTE-mediated reporter gene expression and promotes nuclear export of unspliced mRNA in transfected cells. Taken together, these data support the proposal that HAP95 specifically facilitates CTE-mediated gene expression by directly binding to RHA.
Active Transport, Cell Nucleus↗
Preliminary X-ray crystallographic analysis of a Ca2+-binding protein human S100A1.
S100A1, a Ca(2+)-binding protein from the S100 protein family, has been crystallized by the vapour-diffusion method using polyethylene glycol 4000 as the precipitant at pH 8.5. The crystal belongs to space group P6(3). The unit-cell parameters are a = b = 57.3, c = 104.7 A. There appear to be two S100A1 molecules in the asymmetric unit. The crystals were stable during exposure to X-rays and diffract to 2.6 A resolution in-house.
Calcium-Binding Proteins↗
Progress toward the total synthesis of ingenol: construction of the complete carbocyclic skeleton.
[reaction: see text] The complete carbocyclic skeleton of ingenol is assembled via a route that employs ring-closing metathesis (RCM) to close the strained "inside-outside" BC ring system (i.e., 24 --> 25).
Anti-HIV Agents↗
CD147 facilitates HIV-1 infection by interacting with virus-associated cyclophilin A.
Cyclophilin A (CyPA) is specifically incorporated into the virions of HIV-1 and has been shown to enhance significantly an early step of cellular HIV-1 infection. Our preliminary studies implicated CD147 as a receptor for extracellular CyPA. Here, we demonstrate a role for CyPA-CD147 interaction during the early steps of HIV-1 infection. Expression of human CD147 increased infection by HIV-1 under one-cycle conditions. However, susceptibility to infection by viruses lacking CyPA (simian immunodeficiency virus or HIV-1 produced in the presence of cyclosporin A) was unaffected by CD147. Virus-associated CyPA coimmunoprecipitated with CD147 from infected cells. Antibody to CD147 inhibited HIV-1 entry as evidenced by the delay in translocation of the HIV-1 core proteins from the membrane and inhibition of viral reverse transcription. Viruses whose replication did not require CyPA (SIV or mutant HIV-1) were resistant to the inhibitory effect of anti-CD147 antibody. These results suggest that HIV-1 entry depends on an interaction between virus-associated CyPA and CD147 on a target cell.
Animals↗
Constitutive Sp1 activity is essential for differential constitutive expression of vascular endothelial growth factor in human pancreatic adenocarcinoma.
Vascular endothelial growth factor (VEGF) is a key angiogenic molecule that plays an important role in the growth and metastasis of many types of human cancer, including pancreatic adenocarcinoma. In this study, we explored the regulation of VEGF in human pancreatic cancer cells. Over 70% of the human pancreatic cancer cell lines studied in vitro secreted constitutively high levels of VEGF. High VEGF-secreting cells also generally expressed an elevated steady-state level of VEGF mRNA. Kinetic analysis revealed that the elevated steady-state level of VEGF mRNA was due to enhanced VEGF gene transcription and increased constitutive VEGF promoter activity. Deletive mutation analyses of the VEGF promoter revealed that the region from -109 to -38 bp was essential for constitutive VEGF promoter activity. Further deletion and point mutation analyses indicated that mutation of individual or all of the putative Sp1 binding sites reduced or eliminated the constitutive VEGF promoter activity and abrogated the differential activity of the promoter in high and low VEGF-expressing cells. Consistent with the constitutive VEGF transcription activation, a high level of constitutive Sp1 expression and activity was detected in pancreatic cancer cell lines and pancreatic cancer tissue specimens overexpressing VEGF. Collectively, our data demonstrated that constitutive Sp1 activation is essential for the differential overexpression of VEGF, which in turn plays an important role in the angiogenesis and progression of human pancreatic cancer.
Adenocarcinoma↗
CaM kinase II-dependent suppression of nicotinic acetylcholine receptor delta-subunit promoter activity.
Nerve-induced muscle activity suppresses nicotinic acetylcholine receptor (nAChR) gene expression by increasing intracellular calcium levels. This suppression is mediated by nAChR promoter sequences harboring at least 1 E-box (CANNTG) that bind myogenic helix-loop-helix transcription factors. How muscle depolarization or increased calcium mediates changes in nAChR promoter activity is not well understood. In chick muscle, protein kinase C (PKC) activation is necessary for activity-dependent nAChR gene suppression. Similar effects of PKC activation have not been found in mammalian skeletal muscle. Therefore, we used rat primary muscle cultures to screen for other calcium-regulated enzymatic activities that may mediate the effects of muscle activity and calcium on nAChR promoter activity. We report here that calcium/calmodulin-dependent protein kinase II (CaM kinase II) can specifically suppress nAChR promoter activity in mammalian muscle. This regulation was mediated by a single E-box sequence residing in the previously characterized nAChR delta-subunit genes 47-base pair activity-dependent enhancer. In vitro protein/DNA interaction studies suggest that CaM kinase II inhibits binding of the myogenic factor, myogenin, to the delta-promoter 47-base pair activity-dependent enhancer. CaM kinase activity is increased in active muscle and inhibition of this enzymatic activity results in increased nAChR delta-promoter activity. Therefore, CaM kinase II may represent a previously unappreciated activity that participates in coupling muscle depolarization to nAChR gene expression.
Animals↗