bluuebunny/crossref_metadata_2025_split huggingface dataset:
Roles of protein subunits in RNA–protein complexes: Lessons from ribonuclease P
Authors: Hsieh John , Andrews Andy J. , Fierke Carol A. 
Published: December 2003

AbstractRibonucleoproteins (RNP) are involved in many essential processes in life. However, the roles of RNA and protein subunits in an RNP complex are often hard to dissect. In many RNP complexes, including the ribosome and the Group II introns, one main function of the protein subunits is to facilitate RNA folding. However, in other systems, the protein subunits may perform additional functions, and can affect the biological activities of the RNP complexes. In this review, we use ribonuclease P (RNase P) as an example to illustrate how the protein subunit of this RNP affects different aspects of catalysis. RNase P plays an essential role in the processing of the precursor to transfer RNA (pre‐tRNA) and is found in all three domains of life. While every cell has an RNase P (ribonuclease P) enzyme, only the bacterial and some of the archaeal RNase P RNAs (RNA component of RNase P) are active in vitro in the absence of the RNase P protein. RNase P is a remarkable enzyme in the fact that it has a conserved catalytic core composed of RNA around which a diverse array of protein(s) interact to create the RNase P holoenzyme. This combination of highly conserved RNA and altered protein components is a puzzle that allows the dissection of the functional roles of protein subunits in these RNP complexes. © 2003 Wiley Periodicals, Inc. Biopolymers 73: 79–89, 2004
Hydration dependence of backbone and side chain polylysine dynamics: A 13C solid‐state NMR and IR spectroscopy study
Authors: Krushelnitsky Alexey , Faizullin Dzhigangir , Reichert Detlef 
Published: December 2003

AbstractThe molecular dynamics of solid poly‐L‐lysine has been studied by the following natural abundance 13C‐NMR relaxation methods: measurements of the relaxation times T1 at two resonance frequencies, off‐resonance T1ρ at two spin‐lock frequencies, and proton‐decoupled T1ρ. Experiments were performed at different temperatures and hydration levels (up to 17% H2O by weight). The natural abundance 13C‐CPMAS spectrum of polylysine provides spectral resolution of all types of backbone and side chain carbons and thus, dynamic parameters could be determined separately for each of them. At the same time, the conformational properties of polylysine were investigated by Fourier transform infrared spectroscopy. The data obtained from the different NMR experiments were simultaneously analyzed using the correlation function formalism and model‐free approach. The results indicate that in dry polylysine both backbone and side chains take part in two low amplitude motions with correlation times of the order of 10−4 s and 10−9 s. Upon hydration, the dynamic parameters of the backbone remain almost constant except for the amplitude of the slower process that increases moderately. The side chain dynamics reveals a much stronger hydration response: the amplitudes of both slow and fast motions increase significantly and the correlation time of the slow motion shortens by about five orders of magnitude, and at hydration levels of more than 10% H2O fast and slow side chain motions are experimentally indistinguishable. These changes in the molecular dynamics cannot be ascribed to any hydration‐dependent conformational transitions of polylysine because IR spectra reveal almost no hydration dependence in either backbone or side chain absorption domains. The physical nature of the fast and slow motions, their correlation time distributions, and hydration dependence of microdynamic parameters are discussed. © 2003 Wiley Periodicals, Inc. Biopolymers 73: 1–15, 2004
Synthesis of Tissues and Organs
Authors: Yannas Ioannis V. 
Published: December 2003

AbstractSymbolism that describes the synthetic processes for chemical compounds has been used to describe, in qualitative terms, the synthesis of tissues and organs at the correct anatomical site. The synthetic process is summarized in the reaction diagram, a shorthand representation of the reactants, reactor, and products. Analysis of a large number of independent protocols has led to identification of the simplest synthetic pathways for two organs that have been studied extensively: skin and peripheral nerves. These apparently irreducible reaction diagrams for the two organs are not only simple but surprisingly similar, a fact suggesting the existence of general rules for the synthesis of other organs as well. The only two reactants that are required are an active scaffold (a macromolecular network synthesized as a highly porous analogue of the extracellular matrix) and a seeding of epithelial cells of the organ being synthesized. Scaffolds possessed biological (regenerative) activity provided that they were capable of blocking the contraction process that leads to closure of the injured site. Such activity requires that the density of ligands for binding of contractile cells on the scaffold maintains a sufficiently high level over the period of synthesis.
Recognition of Planar and Nonplanar Ligands in the Malachite Green–RNA Aptamer Complex
Authors: Flinders Jeremy , DeFina Steven C. , Brackett David M. , Baugh Chris , Wilson Charles , Dieckmann Thorsten 
Published: December 2003

AbstractRibonucleic acids are an attractive drug target owing to their central role in many pathological processes. Notwithstanding this potential, RNA has only rarely been successfully targeted with novel drugs. The difficulty of targeting RNA is at least in part due to the unusual mode of binding found in most small‐molecule–RNA complexes: the ligand binding pocket of the RNA is largely unstructured in the absence of ligand and forms a defined structure only with the ligand acting as scaffold for folding. Moreover, electrostatic interactions between RNA and ligand can also induce significant changes in the ligand structure due to the polyanionic nature of the RNA. Aptamers are ideal model systems to study these kinds of interactions owing to their small size and the ease with which they can be evolved to recognize a large variety of different ligands. Here we present the solution structure of an RNA aptamer that binds triphenyl dyes in complex with malachite green and compare it with a previously determined crystal structure of a complex formed with tetramethylrosamine. The structures illustrate how the same RNA binding pocket can adapt to accommodate both planar and nonplanar ligands. Binding studies with single‐ and double‐substitution mutant aptamers are used to correlate three‐dimensional structure with complex stability. The two RNA–ligand complex structures allow a discussion of structural changes that have been observed in the ligand in the context of the overall complex structure. Base pairing and stacking interactions within the RNA fold the phosphate backbone into a structure that results in an asymmetric charge distribution within the binding pocket that forces the ligand to adapt through a redistribution of the positive partial charge.
Fungal Aerobic Reductive Dechlorination of Ethyl 2‐Chloroacetoacetate by Saccharomyces cerevisiae: Mechanism of a Novel Type of Microbial Dehalogenation
Authors: Jörg Gerhard , Bertau Martin 
Published: December 2003

AbstractSaccharomyces cerevisiae reduces the β‐keto ester ethyl 2‐chloroacetoacetate to the respective chiral cis‐ and trans‐β‐hydroxy esters. In the course of chiral reduction, competing dehalogenation of the xenobiotic substrate to ethyl acetoacetate occurs, in a reaction mediated by cytosolic glutathione (GSH). Mechanistically, the dechlorination is a novel type of glutathione‐dependent dehalogenation catalysed by an as yet unidentified glutathione‐dependent dehalogenase. The first step consists of a nucleophilic replacement of the chloride substituent by glutathione. In the subsequent enzyme‐catalysed step, a second glutathione molecule liberates the dehalogenation product by thiolytic attack at the thioether bridge, resulting in a net transfer of two electrons to the substrate and in the formation of glutathione disulfide (GSSG). Being effective under aerobic conditions and catalysed by a fungus, this reductive dechlorination of an aliphatic substrate is an outstanding example of a novel, glutathione‐mediated microbial dehalogenation.
Structure Investigation of TiIV‐BODOLates Involved in the Catalytic Asymmetric Reduction of Ketones Using Catecholborane
Authors: Sarvary Ian , Norrby Per‐Ola , Frejd Torbjörn 
Published: December 2003

AbstractThe complexes formed by the reaction of [Ti(OiPr)4] and bicyclo‐octanediols (BODOLs) 1 and 2 (1:1) are useful as chiral catalysts in asymmetric reductions and were investigated by 1H NMR spectroscopy and computational methods. A consistent picture emerged of head‐to‐tail dimers being kept together via a Ti‐O‐Ti‐O μ‐oxo bridge similar to the Ti‐tartrates but different from the corresponding Ti‐BINOLates and Ti‐TADDOLates.
Acid–Base Sensors Based on Novel Quinone‐Type Dyes
Authors: Elhabiri Mourad , Siri Olivier , Sornosa‐Tent Alejandra , Albrecht‐Gary Anne‐Marie , Braunstein Pierre 
Published: December 2003

AbstractWe present a detailed study on the acid–base behaviour of a family of “potentially antiaromatic” p‐benzoquinonediimine ligands. These 12π electron molecules can be considered as constituted of two chemically connected but electronically not conjugated 6π‐electron subunits. Upon successive protonation, “mono” and “double” cyanine‐type chromophores are generated in solution and allow a precise and sensitive spectrophotometric detection. These molecules represent a new class of tunable quinones whose electronic and structural properties can be triggered by proton input, as established by a complete physico‐chemical study involving a combination of potentiometric and spectrophotometric methods (absorption and emission).
Chiral Xyliphos Complexes for the Catalytic Imine Hydrogenation Leading to the Metolachlor Herbicide: Isolation of Catalyst–Substrate Adducts
Authors: Dorta Romano , Broggini Diego , Stoop Robert , Rüegger Heinz , Spindler Felix , Togni Antonio 
Published: December 2003

AbstractIridium complexes relevant to the catalytic enantioselective hydrogenation of 2‐methyl‐6‐ethylphenyl‐1′‐methyl‐2′‐methoxyethylimine (MEA‐imine, 1) in the Syngenta Metolachlor (3) process were prepared and characterized. Reaction of the diphosphane (S)‐1‐[(R)‐2‐(diphenylphosphanyl)ferrocenyl]ethyldi(3,5‐xylyl)phosphane ((S)‐(R)‐Xyliphos, (S)‐(R)‐4) with [Ir2(μ‐Cl)2(cod)2] (cod=1,5‐cyclooctadiene) afforded [Ir(Cl)(cod){(S)‐(R)‐4}] (7), which reacted with AgBF4 to form [Ir(cod){(S)‐(R)‐4}]BF4 (8). Complexes 7 and 8 reacted with iodide to yield [Ir(I)(cod){(S)‐(R)‐4}] (9). When 9 was treated with one and two equivalents of HBF4, two isomers of the cationic IrIII iodo hydrido complex [Ir(I)(H)(cod){(S)‐(R)‐4}]BF4 were isolated (10 and 11, respectively). Complex 9 was oxidized with one equivalent of I2 to give the iodo‐bridged dinuclear species [Ir2I2(μ‐I)3{(S)‐(R)‐4}2)]I (12). [Ir2(μ‐Cl)2(coe)4] (coe=cyclooctene) reacted with (S)‐(R)‐4 to yield the chloro‐bridged dinuclear complex [Ir2(μ‐Cl)2{(S)‐(R)‐4}2] (13). Complexes 7–12 were structurally characterized by single‐crystal X‐ray diffraction and tested as single‐component catalyst precursors for enantioselective hydrogenation of MEA‐imine. Complex 10 and dinuclear complex 12 gave the best catalytic results. Efforts were also directed at isolating substrate– or product–catalyst adducts: Treatment of 8 with 2,6‐dimethylphenyl‐1′‐methyl‐2′‐methoxyethylimine (DMA‐imine, 14, a model for 1) under H2 allowed four isomers of [Ir(H)2{(S)‐(R)‐4}(14)]BF4 (18–21) to be isolated. These analytically pure isomers were fully characterized by 2D NMR techniques. X‐ray structural analysis of an IrI–imine adduct, namely, [Ir(C2H4)2(14)]BF4 (25), which was prepared by reacting [IrCl(C2H4)4] with [Ag(14)2]BF4 (16), confirmed the κ2 coordination mode of imine 14.
A Unique Binaphthyl Strapped Iron–Porphyrin Catalyst for the Enantioselective Epoxidation of Terminal Olefins
Authors: Rose Eric , Ren Qi‐Zhi , Andrioletti Bruno 
Published: December 2003

AbstractA new chiral binaphthyl‐strapped iron–porphyrin 4 b that exhibits unprecedented catalytic activity toward the enantioselective epoxidation of terminal olefins was synthesized. Typical enantiomeric excesses (ee) of 90 % were measured with a maximum of 97 % for the epoxidation of styrene, whereas the turnover numbers (TON) averaged 16 000.
Polyoxotungstate Photoinduced Alkylation of Electrophilic Alkenes by Cycloalkanes
Authors: Dondi Daniele , Fagnoni Maurizio , Molinari Alessandra , Maldotti Andrea , Albini Angelo 
Published: December 2003

AbstractAlkyl radical obtained by irradiation of tetrabutylammonium decatungstate in acetonitrile in the presence of cycloalkanes (C5H10, C6H12, C7H14) are efficiently trapped by electrophilic alkenes (acrylonitrile, isopropylydenmalonitrile, isopropylydencyanoacetate) to give the corresponding alkylated aliphatic nitriles. The reaction can be carried out up to complete conversion of the alkene with reasonable (in most cases 60–65 %) yields. Addition of the radicals to the alkene is followed by electron transfer from reduced decatungstate regenerating the sensitizer (turn over number up to 60). Steady‐state measurements, EPR evidence, deuteration experiments and attempted intramolecular trapping of the adduct radical support the mechanistic proposal.
Ruthenium‐Catalyzed One‐Pot Double Allylation/Cycloisomerization of 1,3‐Dicarbonyl Compounds Leading to exo‐Methylenecyclopentanes
Authors: Yamamoto Yoshihiko , Nakagai Yu‐ichiro , Itoh Kenji 
Published: December 2003

AbstractThe ruthenium‐catalyzed one‐pot double allylation/cycloisomerization of 1,3‐diketones and methyl acetoacetate gave exo‐methylenecyclopentanes in moderate to good yields with high isomer selectivity. The double allylation step effectively proceeded in the presence of a RuII precatalyst, [Cp*RuCl(cod)], in 1,2‐dichloroethane at 90 °C. The subsequent cycloisomerization was carried out upon addition of triethylsilane as a hydride source without purification of a 1,6‐diene intermediate. Detailed inspections of the reaction by 1H NMR spectroscopy disclosed that triethylsilyl methyl ether plays an important role for the conversion of a ruthenium(IV) allyl complex formed in the double allylation step into a ruthenium(II) species required for the cycloisomerization.
Metal‐Induced Tautomerization of p‐ to o‐Quinone Compounds: Experimental Evidence from CuI and ReI Complexes of Azophenine and DFT Studies
Authors: Frantz Stéphanie , Rall Jochen , Hartenbach Ingo , Schleid Thomas , Záliš Stanislav , Kaim Wolfgang 
Published: December 2003

AbstractAzophenine (7,8‐diphenyl‐2,5‐bis(phenylamino)‐p‐quinonediimine, Lp) reacts with [Cu(PPh3)4](BF4) or [Re(CO)5Cl] to yield the (Ph3P)2Cu+ or [(OC)3ClRe] complex of the tautomeric form 7,8‐diphenyl‐4,5‐bis(phenylamino)‐o‐quinonediimine, Lo, as evident from structure determinations and from very intense metal‐to‐ligand charge transfer (MLCT) transitions in the visible region. Time‐dependent DFT (TD‐DFT) calculations on model complexes [(N∩N)Re(CO)3Cl] confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o‐quinonediimine complexes in comparison to compounds with N∩N=1,4‐dialkyl‐1,4‐diazabutadiene. The complexes are additionally stabilized through hydrogen bonding between two now ortho‐positioned NHPh substituents and one fluoride of the BF4− anion (Cu complex) or the chloride ligand (Re complex). DFT Calculations on the model ligands p‐quinonediimine or 2,5‐diamino‐p‐quinonediimine and their ortho‐quinonoid forms with and without Li+ or Cu+ are presented to discuss the relevance for metal‐dependent quinoproteins.
Formamidine Ureas as Tunable Electrophiles
Authors: Díaz David D. , Finn M. G. 
Published: December 2003

AbstractFormamidine urea compounds exchange imine fragments with primary nitrogen nucleophiles, allowing the preparation of a variety of derivatives from a single precursor. The reactivities of these species are governed primarily by the electron‐donating power of the substituents and are tunable over a range of >103 in first‐order rates of hydrolysis.
Selective Synthesis and Characterization of Single‐Crystal Silver Molybdate/Tungstate Nanowires by a Hydrothermal Process
Authors: Cui Xianjin , Yu Shu‐Hong , Li Lingling , Biao Liu , Li Huabin , Mo Maosong , Liu Xian‐Ming 
Published: December 2003

AbstractSelective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag2MoO4 and Ag6Mo10O33 can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo17O47, Ag2Mo2O7, Ag6Mo10O33 were observed under different pH conditions. Ag6Mo10O33 nanowires with uniform diameter 50–60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 °C. The melting point of Ag6Mo10O33 nanowires were found to be about 238 °C. Similarly, Ag2WO4, and Ag2W2O7 nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale.
Highly Efficient Biomimetic Total Synthesis and Structural Verification of Bistratamides E and J from Lissoclinum bistratum
Authors: You Shu‐Li , Kelly Jeffery W. 
Published: December 2003

AbstractThe interesting biological activities of heterocycle‐containing cyclic peptide‐derived natural products, isolated from marine organisms over the past twenty years, have attracted the interest of many synthetic and natural products chemists. Bistratamides E–J, members of this class of natural products that were isolated very recently from Lissoclinum bistratum, exhibited cytotoxic activity against a human colon tumor (HCT‐116) cell line. Here we report the first total syntheses of bistratamides E (1) and J (2) in overall yields of 19 and 34 %, respectively. The thiazole substructures have been synthesized by oxidation of their corresponding thiazoline substructures, which were obtained from cysteine containing peptides using a novel biomimetic approach wherein Val‐Cys dipeptide units were converted to thiazolines by a bisphosphonium salt. The final macrocyclization was promoted efficiently using the combination of PyBOP and DMAP. This approach allows the use of readily available Fmoc‐protected amino acids to make complex thiazole and oxazoline‐containing natural products.
Nanocage Encapsulation of Two ortho‐Carborane Molecules
Authors: Raston Colin L. , Cave Gareth W. V. 
Published: December 2003

AbstractBowl‐shaped C‐methylcalix[4]resorcinarene forms a 1:1 ball‐and‐socket nanostructure with o‐carborane through two endo‐cavity BCH⋅⋅⋅π hydrogen bonds. In the presence of 4′,2:6,4′′‐terpyridine, two of these nanostructures are held together by four terpyridines through sixteen OH⋅⋅⋅N hydrogen bonds, completely shrouding two carboranes.
The βII isotype of tubulin is present in the cell nuclei of a variety of cancers
Authors: Yeh I‐Tien , Ludueña Richard F. 
Published: December 2003

AbstractTubulin, the subunit protein of microtubules, has generally been thought to be exclusively a cytoplasmic protein in higher eukaryotes. We have previously shown that cultured rat kidney mesangial cells contain the βII isotype of tubulin in their nuclei in the form of an αβII dimer [Walss et al., 1999: Cell Motil. Cytoskeleton 42:274–284, 1999]. More recently, we examined a variety of cancerous and non‐cancerous cell lines and found βII in the nuclei of all of the former and only a few of the latter (Walss‐Bass et al., 2002: Cell Tissue Res. 308:215–223]. In order to determine if βII‐tubulin occurs in the nuclei of actual cancers as well as in cancer cell lines, we used the immunoperoxidase method to look for nuclear βII in a variety of tumors excised from 201 patients. We found that 75% of these tumors contain βII in their nuclei. Distribution of nuclear βII was highly dependent on the type of cancer, with 100% of the colon and prostate cancers, but only 19% of the skin tumors, having nuclear βII. Nuclear βII was particularly marked in tumors of epithelial origin, of which 83% showed nuclear βII, in contrast to 54% in tumors of non‐epithelial origin. In many cases, βII staining occurred very strongly in the nuclei and not in the cytoplasm; in other cases, βII was present in both. In many cases, particularly metastases, otherwise normal cells adjacent to the tumor also showed nuclear βII, suggesting that cancer cells may influence nearby cells to synthesize βII and localize it to their nuclei. Our results have implications for the diagnosis, biology, and chemotherapy of cancer. Cell Motil. Cytoskeleton 57:96–106, 2004. © 2004 Wiley‐Liss, Inc.
Myosin‐mediated cytoskeleton contraction and Rho GTPases regulate laminin‐5 matrix assembly
Authors: deHart Gregory W. , Jones Jonathan C. R. 
Published: December 2003

AbstractLaminin‐5 is a major structural element of epithelial tissue basement membranes. In the matrix of cultured epithelial cells, laminin‐5 is arranged into intricate patterns. Here we tested a hypothesis that myosin II‐mediated actin contraction is necessary for the proper assembly of a laminin‐5 matrix by cultured SCC12 epithelial cells. To do so, the cells were treated with ML‐7, a myosin II light chain kinase inhibitor, or Y‐27632, an inhibitor of Rho‐kinase (ROCK), both of which block actomyosin contraction. Under these conditions, laminin‐5 shows an aberrant localization in dense patches at the cell periphery. Since ROCK activity is regulated by the small GTPase Rho, this suggests that members of the Rho family of GTPases may also be important for laminin‐5 matrix assembly by SCC12 cells. We confirmed this hypothesis since SCC12 cells expressing mutant proteins that inhibit RhoA, Rac, and Cdc42 assemble the same aberrant laminin‐5 protein arrays as drug‐treated cells. We have also evaluated the organization of the laminin‐5 receptors α3β1 and α6β4 integrin and hemidesmosome proteins in ML‐7‐ and Y‐27632‐treated cells or in cells in which RhoA, Rac, and Cdc42 activity were inhibited. In all instances, α3β1 and α6β4 integrin heterodimers, as well as hemidesmosome proteins, localize precisely with laminin‐5 in the matrix of the cells. In summary, our results provide evidence that myosin II‐mediated actin contraction and the activity of Rho GTPases are necessary for the proper organization of a laminin‐5 matrix and localization of hemidesmosome protein arrays in epithelial cells. Cell Motil. Cytoskeleton 57:107–117, 2004. © 2004 Wiley‐Liss, Inc.