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  • 1
    Publication Date: 1997-04-18
    Description: The three-dimensional structure of the enzyme 3-oxo-delta5-steroid isomerase (E.C. 5.3.3.1), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy. The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interactions. Each monomer comprises three alpha helices and a six-strand mixed beta-pleated sheet arranged to form a deep hydrophobic cavity. Catalytically important residues Tyr14 (general acid) and Asp38 (general base) are located near the bottom of the cavity and positioned as expected from mechanistic hypotheses. An unexpected acid group (Asp99) is also located in the active site adjacent to Tyr14, and kinetic and binding studies of the Asp99 to Ala mutant demonstrate that Asp99 contributes to catalysis by stabilizing the intermediate.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wu, Z R -- Ebrahimian, S -- Zawrotny, M E -- Thornburg, L D -- Perez-Alvarado, G C -- Brothers, P -- Pollack, R M -- Summers, M F -- GM38155/GM/NIGMS NIH HHS/ -- GM49082/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1997 Apr 18;276(5311):415-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9103200" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Androstenedione/metabolism ; Binding Sites ; Dimerization ; Estradiol/metabolism ; Hydrogen Bonding ; Magnetic Resonance Spectroscopy ; Models, Molecular ; Molecular Sequence Data ; Mutagenesis, Site-Directed ; *Protein Conformation ; Protein Structure, Secondary ; Solutions ; Steroid Isomerases/*chemistry/genetics/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 1998-02-07
    Description: The three-dimensional structure of the human immunodeficiency virus-type 1 (HIV-1) nucleocapsid protein (NC) bound to the SL3 stem-loop recognition element of the genomic Psi RNA packaging signal has been determined by heteronuclear magnetic resonance spectroscopy. Tight binding (dissociation constant, approximately 100 nM) is mediated by specific interactions between the amino- and carboxyl-terminal CCHC-type zinc knuckles of the NC protein and the G7 and G9 nucleotide bases, respectively, of the G6-G7-A8-G9 RNA tetraloop. A8 packs against the amino-terminal knuckle and forms a hydrogen bond with conserved Arg32, and residues Lys3 to Arg10 of NC form a 310 helix that binds to the major groove of the RNA stem and also packs against the amino-terminal zinc knuckle. The structure provides insights into the mechanism of viral genome recognition, explains extensive amino acid conservation within NC, and serves as a basis for the development of inhibitors designed to interfere with genome encapsidation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉De Guzman, R N -- Wu, Z R -- Stalling, C C -- Pappalardo, L -- Borer, P N -- Summers, M F -- GM32691/GM/NIGMS NIH HHS/ -- GM42561/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1998 Jan 16;279(5349):384-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Maryland-Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9430589" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Base Sequence ; Binding Sites ; Gene Products, gag/*chemistry/metabolism ; Genome, Viral ; HIV-1/*chemistry/genetics ; Hydrogen Bonding ; Magnetic Resonance Spectroscopy ; Models, Molecular ; Molecular Sequence Data ; Nucleic Acid Conformation ; Nucleocapsid/*chemistry/metabolism ; Protein Conformation ; Protein Folding ; Protein Structure, Secondary ; RNA, Viral/*chemistry/genetics/metabolism ; Zinc/chemistry/metabolism ; Zinc Fingers
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2018-06-16
    Description: A power grid reactive power optimization algorithm was proposed in this paper to ensure that distribution network systems run efficiently, which is called the opposition-based chaos shuffled frog leaping algorithm (OCSFLA). A mathematical model of reactive power optimization was established based on the consideration of the constraint conditions. The initial swarm of the model was optimized based on the opposition strategy. The leading role changed gradually from the shuffled frog leaping algorithm to chaotic search in the iterative process by setting the appropriate chaotic variables. Thus, the global optimal solution was searched more quickly. In the simulation tests of the IEEE30 system, the results show that a better compensation effect was obtained when the reactive power compensation was performed in nodes 12 and 24. After completing the reactive power optimization based on the improved leapfrog algorithm, the active network loss value of the system was reduced by 13.85%. ...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 4
    Publication Date: 2012-02-29
    Description: Phenotypic plasticity occurs prevalently and plays a vital role in adaptive evolution. However, the underlying molecular mechanisms responsible for the expression of alternate phenotypes remain unknown. Here, a density-dependent phase polyphenism of Locusta migratoria was used as the study model to identify key signaling molecules regulating the expression of phenotypic plasticity. Metabolomic analysis, using high-performance liquid chromatography and gas chromatography–mass spectrometry, showed that solitarious and gregarious locusts have distinct metabolic profiles in hemolymph. A total of 319 metabolites, many of which are involved in lipid metabolism, differed significantly in concentration between the phases. In addition, the time course of changes in the metabolic profiles of locust hemolymph that accompany phase transition was analyzed. Carnitine and its acyl derivatives, which are involved in the lipid β-oxidation process, were identified as key differential metabolites that display robust correlation with the time courses of phase transition. RNAi silencing of two key enzymes from the carnitine system, carnitine acetyltransferase and palmitoyltransferase, resulted in a behavioral transition from the gregarious to solitarious phase and the corresponding changes of metabolic profiles. In contrast, the injection of exogenous acetylcarnitine promoted the acquisition of gregarious behavior in solitarious locusts. These results suggest that carnitines mediate locust phase transition possibly through modulating lipid metabolism and influencing the nervous system of the locusts.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 5
    Publication Date: 2013-10-09
    Description: Deposition of insoluble protein aggregates is a hallmark of neurodegenerative diseases. The universal presence of β-amyloid and tau in Alzheimer’s disease (AD) has facilitated advancement of the amyloid cascade and tau hypotheses that have dominated AD pathogenesis research and therapeutic development. However, the underlying etiology of the disease remains to...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 6
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2018-10-13
    Description: The transition from nanocluster to nanocrystal is a central issue in nanoscience. The atomic structure determination of metal nanoparticles in the transition size range is challenging and particularly important in understanding the quantum size effect at the atomic level. On the basis of the rationale that the intra- and interparticle weak interactions play critical roles in growing high-quality single crystals of metal nanoparticles, we have reproducibly obtained ideal crystals of Au 144 (SR) 60 and successfully solved its structure by x-ray crystallography (XRC); this structure was theoretically predicted a decade ago and has long been pursued experimentally but without success until now. Here, XRC reveals an interesting Au 12 hollow icosahedron in thiolated gold nanoclusters for the first time. The Au–Au bond length, close to that of bulk gold, shows better thermal extensibility than the other Au–Au bond lengths in Au 144 (SR) 60 , providing an atomic-level perspective because metal generally shows better thermal extensibility than nonmetal materials. Thus, our work not only reveals the mysterious, long experimentally pursued structure of a transition-sized nanoparticle but also has important implications for the growth of high-quality, single-crystal nanoparticles, as well as for the understanding of the thermal extensibility of metals from the perspective of chemical bonding.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 7
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2018
    Description: 〈p〉The transition from nanocluster to nanocrystal is a central issue in nanoscience. The atomic structure determination of metal nanoparticles in the transition size range is challenging and particularly important in understanding the quantum size effect at the atomic level. On the basis of the rationale that the intra- and interparticle weak interactions play critical roles in growing high-quality single crystals of metal nanoparticles, we have reproducibly obtained ideal crystals of Au〈sub〉144〈/sub〉(SR)〈sub〉60〈/sub〉 and successfully solved its structure by x-ray crystallography (XRC); this structure was theoretically predicted a decade ago and has long been pursued experimentally but without success until now. Here, XRC reveals an interesting Au〈sub〉12〈/sub〉 hollow icosahedron in thiolated gold nanoclusters for the first time. The Au–Au bond length, close to that of bulk gold, shows better thermal extensibility than the other Au–Au bond lengths in Au〈sub〉144〈/sub〉(SR)〈sub〉60〈/sub〉, providing an atomic-level perspective because metal generally shows better thermal extensibility than nonmetal materials. Thus, our work not only reveals the mysterious, long experimentally pursued structure of a transition-sized nanoparticle but also has important implications for the growth of high-quality, single-crystal nanoparticles, as well as for the understanding of the thermal extensibility of metals from the perspective of chemical bonding.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 8
    Publication Date: 2016-05-25
    Description: Actin, spectrin, and associated molecules form a periodic, submembrane cytoskeleton in the axons of neurons. For a better understanding of this membrane-associated periodic skeleton (MPS), it is important to address how prevalent this structure is in different neuronal types, different subcellular compartments, and across different animal species. Here, we investigated...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 9
    Publication Date: 2016-09-15
    Description: A new scintillator-based fast ion loss detector (FILD) has been installed on Experimental Advanced Superconducting Tokamak (EAST) to investigate the fast ion loss behavior in high performance plasma with neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). A two dimensional 40 mm × 40 mm scintillator-coated (ZnS:Ag) stainless plate is mounted in the front of the detector, capturing the escaping fast ions. Photons from the scintillator plate are imaged with a Phantom V2010 CCD camera. The lost fast ions can be measured with the pitch angle from 60° to 120° and the gyroradius from 10 mm to 180 mm. This paper will describe the details of FILD diagnostic on EAST and describe preliminary measurements during NBI and ICRH heating.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 10
    Publication Date: 2017-02-18
    Description: Deformation force and forming quality are the important research focus in process of Magnesium (Mg) alloy wheel. In this paper, a process model of flow control forming (FCF) for the wheel was built, and its finite element model was given to simulate the FCF process at different extrusion speed (5 mm/s, 10 mm/s, 15 mm/s and 20 mm/s). The simulated results show that the FCF method for the wheel can reduce deformation force to less than 22000 kN, while there are cracks on rim of the wheel. The results are verified by the experiment and the cracks predicted by simulation are in good agreement with the experimental results.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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