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1.
Antoni Planas Juan Nieto Mireia Abel Antoni Segade 《Biocatalysis and Biotransformation》2013,31(4-5):223-231
AbstractIn the mechanism of retaining β-glycosidases, the 2-hydroxyl group of the substrate in the monosaccharyl unit involved in catalysis (subsite -1) is beleived to play an important role through hydrogen bonding interactions with protein residues that are optimized at the transition state. Commonly, removal of the 2-OH group of the substrate results in a 10–12 kcal·mol-1 transition state destabilization. However, this effect seems not to be general as reported here for Bacillus 1,3-1,4-β-glucanase, a family 16 retaining endo-glycosidase. A p-nitrophenol 2-deosxy tetrasaccharide substrate was synthesized to probe the involvement of the 2-OH group in catalysis. Comparative kinetics with wild-type and subsite +1 mutants show that the 2-deoxy analog is a better substrate than the corresponding 2-hydroxy substrate. It is tentatively proposed that the 2-deoxy analog adopts a different conformation upon binding that compensates for the lack of the 2-OH substituent. 相似文献
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Kanavarioti Anastassia Lee Lynn F. Gangopadhyay Sumana 《Origins of life and evolution of the biosphere》1999,29(5):473-487
Phosphoimidazolide activated ribomononucleotides (*pN, see structure) are useful substrates for the non-enzymatic synthesis of oligonucleotides. In the presence of metal ions, aqueous solutions of *pN yield primarily the two internucleotide-linked (pN2'pN and pN3'pN) and the pyrophosphate-linked (N5'ppN) dimers. Small amounts of cyclic dimers and higher oligomers are also produced. In this study the relative reactivity of 2-OH vs. 3-OH was determined from the ratio of the yields of pN2'pN vs. pN3'pN. Experiments were performed at 23 °C in the range 7.2 pH 8.4 with substrates that differ in nucleobase (guanosine (G), cytidine (C), uridine (U), and adenosine (A)) and leaving group (imidazole (Im), 2-methylimidazole (2-MeIm) and 2,4-dimethylimidazole (2,4-diMeIm)). Two metal ions (Mg2+ or Mn2+) were employed as catalysts. The conditions used here, i.e. a substrate concentration in the range 0.1 M to 1.0 M and metal ion concentration in the range 0.05 M to 0.2 M, favor base-stacking interactions. The ratio pN2'pN: pN3'pN = 2-5: 3-5 was found independent of nucleobase and typically varied between 2 to 3 indicating that the 2-OH is about 2 to 3 times more reactive than the 3-OH. *pN with Im, compared to 2-MeIm and 2,4-diMeIm leaving group, produce lower yields of internucleotide linked dimers, and a higher pN2'pN: pN3'pN ratio. Trends in the data, observed with all three leaving groups, suggest an increase in pN2'pN: pN3'pN ratio with decreasing substrate concentration (up to 5.47 with 0.051 M ImpG). The observations are in accord with earlier studies reporting a relative reactivity 2'-5': 3'-5'= 6 to 9 obtained with Im as the leaving group, in dilute nucleotide solutions and under conditions that disfavor stacking. It is speculated that the concentration induced change in the relative reactivity is the result of self-association via base-stacking that enhances selectively the proximity of the 3-OH of one molecule to the reactive P-N bond of an other molecule. The implication of these conclusions for oligomerization/ligation reactions is discussed. 相似文献
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Bacteriophages φ29 and Nf from Bacillus subtilis start replication of their linear genomes at both ends using a protein-primed mechanism by means of which the DNA polymerase initiates replication by adding dAMP to the terminal protein, this insertion being directed by the second and third 3′ terminal thymine of the template strand, respectively. In this work, we have obtained evidences about the role of the 3′ terminal base during the initiation steps of φ29 and Nf genome replication. The results indicate that the absence of the 3′ terminal base modifies the initiation position carried out by φ29 DNA polymerase in such a way that now the third position of the template, instead of the second one, guides the incorporation of the initiating nucleotide. In the case of Nf, although the lack of the 3′ terminal base has no effect on the initiation position, its absence impairs further elongation of the TP-dAMP initiation product. The results show the essential role of the 3′ terminal base in guaranteeing the correct positioning of replication origins at the polymerization active site to allow accurate initiation of replication and further elongation. 相似文献
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Jan Milecki Piotr Dembek Wieslaw Z. Antkowiak Zofia Gdaniec Slawomir Mielewczyk Ryszard W. Adamiak 《Nucleosides, nucleotides & nucleic acids》2013,32(4):463-474
Abstract 31P NMR spectroscopy has been used for evaluation of 2′-O-t-BDMSi group migration during reactions of suitably protected 3′-OH ribonucleosides with P(V) and P(III) reagents used in major methodologies for oligoribonucleotide synthesis. 相似文献
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Elisa Ciraolo Fulvio Morello Robin M. Hobbs Frieder Wolf Romina Marone Manuela Iezzi Xiaoyun Lu Giulio Mengozzi Fiorella Altruda Giovanni Sorba Kaomei Guan Pier Paolo Pandolfi Matthias P. Wymann Emilio Hirsch 《Molecular biology of the cell》2010,21(5):704-711
Phosphoinositide 3-kinases (PI3K) are key molecular players in male fertility. However, the specific roles of different p110 PI3K catalytic subunits within the spermatogenic lineage have not been characterized so far. Herein, we report that male mice expressing a catalytically inactive p110β develop testicular hypotrophy and impaired spermatogenesis, leading to a phenotype of oligo-azoospermia and defective fertility. The examination of testes from p110β-defective tubules demonstrates a widespread loss in spermatogenic cells, due to defective proliferation and survival of pre- and postmeiotic cells. In particular, p110β is crucially needed in c-Kit–mediated spermatogonial expansion, as c-Kit–positive cells are lost in the adult testis and activation of Akt by SCF is blocked by a p110β inhibitor. These data establish that activation of the p110β PI3K isoform by c-Kit is required during spermatogenesis, thus opening the way to new treatments for c-Kit positive testicular cancers. 相似文献
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Chunxia Chen Somdeb Mitra Magdalena Jonikas Joshua Martin Michael Brenowitz Alain Laederach 《Biophysical journal》2013,104(6):1326-1337
Many RNA molecules exert their biological function only after folding to unique three-dimensional structures. For long, noncoding RNA molecules, the complexity of finding the native topology can be a major impediment to correct folding to the biologically active structure. An RNA molecule may fold to a near-native structure but not be able to continue to the correct structure due to a topological barrier such as crossed strands or incorrectly stacked helices. Achieving the native conformation thus requires unfolding and refolding, resulting in a long-lived intermediate. We investigate the role of topology in the folding of two phylogenetically related catalytic group I introns, the Twort and Azoarcus group I ribozymes. The kinetic models describing the Mg2+-mediated folding of these ribozymes were previously determined by time-resolved hydroxyl (⋅OH) radical footprinting. Two intermediates formed by parallel intermediates were resolved for each RNA. These data and analytical ultracentrifugation compaction analyses are used herein to constrain coarse-grained models of these folding intermediates as we investigate the role of nonnative topology in dictating the lifetime of the intermediates. Starting from an ensemble of unfolded conformations, we folded the RNA molecules by progressively adding native constraints to subdomains of the RNA defined by the ⋅OH time-progress curves to simulate folding through the different kinetic pathways. We find that nonnative topologies (arrangement of helices) occur frequently in the folding simulations despite using only native constraints to drive the reaction, and that the initial conformation, rather than the folding pathway, is the major determinant of whether the RNA adopts nonnative topology during folding. From these analyses we conclude that biases in the initial conformation likely determine the relative flux through parallel RNA folding pathways. 相似文献
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Of 100 patients with carcinoma of the bladder seen in the Section of Therapeutic Radiology, University of California, San Francisco, between 1957 and 1962, 59 were accepted for radiation treatment. Fifty had transitional cell carcinoma and were treated with supervolt therapy (1 mev or cobalt-60).Two types of tumors were again found suitable for external irradiation: Papillary carcinomas Grades II and III, as long as they have not, or at least have not massively, invaded muscle; and undifferentiated carcinomas, Grade IV, regardless of degree of extension through the pelvis. The former type, if single, is treated by irradiation for the first recurrence after one attempt with radical transurethral resection. In the presence of multiple lesions at the first examination, radiation therapy is given immediately. The latter type is treated by radiation therapy without any attempt at surgical removal.Of 37 patients, Stages A to C, treated more than three years ago, 14 (38 per cent) lived more than three years and eight (22 per cent) had no cystoscopic or clinical signs of active disease and had normal bladder function. Of 23 patients treated more than five years ago, eight were alive after five years (35 per cent) and four (17 per cent) remained controlled by radiation therapy alone, with normal bladder function.No major complications were observed. In particular, no fibrosis of the bladder occurred. Doses ranged from 5,000 r in five and a half weeks to 6,000 r in seven weeks.A close cooperation between urologic surgeons and radiotherapists during recent years permits long-range treatment planning from the time of diagnosis, which is essential in the effective therapy of carcinoma of the bladder. 相似文献
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Children with minimal brain damage show a characteristic pattern of behavior.Often there are no physical signs of abnormality, but the diagnosis can be made from the history, electroencephalographic tracings, psychologic tests and repeated observations.The behavior is a composite of the effects of the brain damage and the response of the child to his environment. The behavior of the brain-damaged child is frequently so frustrating to parents that attitudes of rejection, withdrawal or excessive punitive measures occur.In the present study, when drugs were given and the child''s behavior improved, the parents were better able to understand the needs of the child and create a better home environment in which there was less frustration and emotional pressure. 相似文献
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C. Thibaudeau N. Nishizono Y. Sumita A. Matsuda J. Chattopadhyaya 《Nucleosides, nucleotides & nucleic acids》2013,32(4-5):1035-1053
Abstract The interplay of enthalpy of the gauche effect (ΔH°GE) of the [X3′-C3′-C4′-O4′] fragment in various 3′-substituted (X) 2′,3′-dideoxythymidine derivatives 1–7 and the inherent anomeric effect drives the two-state North ? South equilibrium in the constituent sugar moiety. The group electronegativity of 3′-OCF3 substituent in Marriott's, Inamoto's and Mullay's scales has been determined from simple calibration graphs correlating the group electronegativity of various 3′-substituents (X) in 2′,3′-dideoxythymidine derivatives 1–7 with the experimental strength (ΔH°GE) of the [X3′-C3′-C4′-O4′] gauche effect. ΔH°GE has been experimentally determined from pseudorotational analyses of temperature-dependent 3JHH coupling constants, and can be used as an unambiguous tool for direct experimental estimation of the group electronegativity of a specific substituent covalently attached to 3′-carbon of 2′,3′-dideoxythymidine, which can be compared, in turn, with the theoretical estimation carried out according to Marriott's or Inamoto's procedure. Inconsistency found between theoretical values in Marriott's and Inamoto's scales, on the one hand, and between our experimental estimate and the theoretical value in Marriott's scale, on the other, have been solved by refining the electronegativity scale using our experimental data for 1–7. 相似文献
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《Prostaglandins & other lipid mediators》2007,82(3-4):113-125
Cytosolic phospholipase A2-α (cPLA2) plays an important role in the release of arachidonic acid and in cell injury. Activation of cPLA2 is dependent on a rise in cytosolic Ca2+ concentration, membrane association via the Ca2+-dependent lipid binding (CaLB) domain, and phosphorylation. This study addresses the activation of cPLA2 via potential association with membrane phosphatidylinositol 4,5-bisphosphate (PIP2), including the role of a “pleckstrin homology (PH)-like” region of cPLA2 (amino acids 263-354). In cells incubated with complement, phorbol myristate acetate + the Ca2+ ionophore, A23187, or epidermal growth factor + A23187, expression of the PH domain of phospholipase C-δ1 (which sequesters membrane PIP2) attenuated cPLA2 activity. Stimulated cPLA2 activity was also attenuated by the expression of cPLA2 135-366, or cPLA2 2-366, and expression of a PIP2-specific 5′-phosphatase. However, in a yeast-based assay that tests the ability of proteins to bind to membrane lipids, including PIP2, with high affinity, only cPLA2 1-200 (CaLB domain) was able to interact with membrane lipids, whereas cPLA2s 135-366, 2-366, 201-648, and 1-648 were unable to do so. Therefore, cPLA2 activity can be modulated by sequestration or depletion of cellular PIP2, although the interaction of cPLA2 with membrane PIP2 appears to be indirect, or of weak affinity. 相似文献
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Yuan Tian Christina J. Crump Yue-Ming Li 《The Journal of biological chemistry》2010,285(42):32549-32556
Processing of the amyloid precursor protein (APP) by β- and γ-secretases generates pathogenic β-amyloid (Aβ) peptides associated with Alzheimer disease (AD), whereas cleavage of APP by α-secretases precludes Aβ formation. Little is known about the role of α-secretase cleavage in γ-secretase regulation. Here, we show that α-secretase-cleaved APP C-terminal product (αCTF) functions as an inhibitor of γ-secretase. We demonstrate that the substrate inhibitory domain (ASID) within αCTF, which is bisected by the α-secretase cleavage site, contributes to this negative regulation because deleting or masking this domain turns αCTF into a better substrate for γ-secretase. Moreover, α-secretase cleavage can potentiate the inhibitory effect of ASID. Inhibition of γ-secretase activity by αCTF is observed in both in vitro and cellular systems. This work reveals an unforeseen role for α-secretase in generating an endogenous γ-secretase inhibitor that down-regulates the production of Aβ. Deregulation of this feedback mechanism may contribute to the pathogenesis of AD. 相似文献
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Gordon F. Williams 《The Western journal of medicine》1961,94(3):171-174
In the application of the broad services now available to assist a child having a major neurologic impairment, the pediatrician occupies an important role owing to his ability to consider the problem of the handicapped child in the context of his specialized knowledge of the developmental process. He thus has a large responsibility for interpretation of the problem to the child, to the parents and to his professional colleagues and for guidance of the rehabilitation regimen within the limits of the child''s developmental readiness for new experiences.The pediatrician has the opportunity to contribute significant clinical observations which may provide stimuli for future basic research and to exercise his skill as a practitioner of preventive medicine.Goals for the future achievement of the child having a major neurologic impairment must be set realistically and with great caution. 相似文献
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Massimo Messa Laura Colombo Elena del Favero Laura Cantù Tatiana Stoilova Alfredo Cagnotto Alessandro Rossi Michela Morbin Giuseppe Di Fede Fabrizio Tagliavini Mario Salmona 《The Journal of biological chemistry》2014,289(35):24143-24152
We recently reported a novel Aβ precursor protein mutation (A673V), corresponding to position 2 of Aβ1–42 peptides (Aβ1–42A2V), that caused an early onset AD-type dementia in a homozygous individual. The heterozygous relatives were not affected as an indication of autosomal recessive inheritance of this mutation. We investigated the folding kinetics of native unfolded Aβ1–42A2V in comparison with the wild type sequence (Aβ1–42WT) and the equimolar solution of both peptides (Aβ1–42MIX) to characterize the oligomers that are produced in the early phases. We carried out the structural characterization of the three preparations using electron and atomic force microscopy, fluorescence emission, and x-ray diffraction and described the soluble oligomer formation kinetics by laser light scattering. The mutation promoted a peculiar pathway of oligomerization, forming a connected system similar to a polymer network with hydrophobic residues on the external surface. Aβ1–42MIX generated assemblies very similar to those produced by Aβ1–42WT, albeit with slower kinetics due to the difficulties of Aβ1–42WT and Aβ1–42A2V peptides in building up of stable intermolecular interaction. 相似文献
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Morphophysiological correlations were studied in medium-aged (20- to 60-year-old) Scots pine trees under the northern taiga conditions. Under various ecological conditions, pine trees developed a well-balanced structure, with close linear relationships between needle and root weight and their cross-section areas in all components of the continuous transport network (the coefficient of determination was between 0.88 and 0.999). When the annual cycle of soluble and insoluble carbohydrate contents was followed in various pine tissues, the total concentrations of soluble and insoluble carbohydrates were maintained at constant and tissue-specific levels, except in the growth period. The maximum level of carbohydrates was observed in all tissues at the beginning of rapid growth, and the minimum, at growth cessation. The qualitative composition and amount of carbohydrates matched the phenological phases of development and were not affected by the ecological growth conditions pertinent to the particular environment. The authors conclude that assimilate synthesis and partitioning are related to structural development, and the state of sink centers determines the attracting capacity, whereas the transport network, from roots to needles, and its conducting capacity are essential for the realization of systemic relationships and the control over growth and development in Pinus sylvestris L. 相似文献
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Chris Christodoulou Sudhir Agrawal Michael J. Gait 《Nucleosides, nucleotides & nucleic acids》2013,32(1-2):341-344
Abstract The 2-(2,4-dinitrobenzenesulphenyloxymethyl)benzoyl (DNBSB) group is proposed as a protecting group for the 5′-position of nucleosides. The DNBSB group may be removed under mild non-acidic conditions and may have potential in solid-phase synthesis of oligoribo- and oligodeoxyribonucleotides. 相似文献
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Wei Lu Csaba F. L��szl�� Zhixin Miao Hao Chen Shiyong Wu 《The Journal of biological chemistry》2009,284(36):24281-24288
UV light induces phosphorylation of the α subunit of the eukaryotic initiation factor 2 (eIF2α) and inhibits global protein synthesis. Both eIF2 kinases, protein kinase-like endoplasmic reticulum kinase (PERK) and general control of nonderepressible protein kinase 2 (GCN2), have been shown to phosphorylate eIF2α in response to UV irradiation. However, the roles of PERK and GCN2 in UV-induced eIF2α phosphorylation are controversial. The one or more upstream signaling pathways that lead to the activation of PERK or GCN2 remain unknown. In this report we provide data showing that both PERK and GCN2 contribute to UV-induced eIF2α phosphorylation in human keratinocyte (HaCaT) and mouse embryonic fibroblast cells. Reduction of expression of PERK or GCN2 by small interfering RNA decreases phosphorylation of eIF2α after UV irradiation. These data also show that nitric-oxide synthase (NOS)-mediated oxidative stress plays a role in regulation of eIF2α phosphorylation upon UV irradiation. Treating the cells with the broad NOS inhibitor NG-methyl-l-arginine, the free radical scavenger N-acetyl-l-cysteine, or the NOS substrate l-arginine partially inhibits UV-induced eIF2α phosphorylation. The results presented above led us to propose that NOS mediates UV-induced eIF2α phosphorylation by activation of both PERK and GCN2 via oxidative stress and l-arginine starvation signaling pathways.UV irradiation inhibits translation initiation through activation of kinases that phosphorylate the α-subunit of eukaryotic initiation factor 2 (eIF2α).2 Two eIF2α kinases, double strand RNA-dependent protein kinase-like ER kinase (PERK) and general control of amino acid biosynthesis kinase (GCN2), are known to phosphorylate the serine 51 of eIF2α in response to UV irradiation (1–4). However, the one or more upstream pathways that activate eIF2α kinase(s) upon UV irradiation are not known. In this report, we provide evidence that UV-induced nitric-oxide synthase (NOS) activation and nitric oxide (NO•) production regulate both PERK and GCN2 activation upon UVB irradiation.Expression of inducible nitric-oxide synthase in a mouse macrophage cell line leads to the phosphorylation of eIF2α and inhibition of translation (5). In cultured neuronal and pancreatic cell lines, production of NO• and peroxynitrite (ONOO−) induces endoplasmic reticulum (ER) stress, which activates PERK and results in cell dysfunction and apoptosis (6–9). Cytokine-stimulated inducible nitric-oxide synthase activation in astrocytes depletes l-arginine and activates GCN2, which phosphorylates eIF2α (10). UV irradiation also activates NOS and elevates cellular NO• (11–13). However, the UV-induced NOS activation and NO• production have never been shown to be related to the activation of eIF2α kinase(s). Now we demonstrate that UV-induced activation of NOS mediates the activation of both PERK and GCN2, which coordinately regulate the phosphorylation of eIF2α. 相似文献
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Chad Gu Andrei Vovk Tiantian Zheng Rob D. Coalson Anton Zilman 《Biophysical journal》2019,116(7):1204-1215
Nuclear pore complexes (NPCs) conduct selective, bidirectional transport across the nuclear envelope. The NPC passageway is lined by intrinsically disordered proteins that contain hydrophobic phenylalanine-glycine (FG) motifs, known as FG nucleoporins (FG nups), that play the key role in the NPC transport mechanism. Cohesive interactions among the FG nups, which arise from the combination of hydrophobic, electrostatic, and other forces, have been hypothesized to control the morphology of the assemblies of FG nups in the NPC, as well as their permeability with respect to the transport proteins. However, the role of FG nup cohesiveness is still vigorously debated. Using coarse-grained polymer theory and numerical simulations, we study the effects of cohesiveness on the selective permeability of in vitro FG nup assemblies in different geometries that have served as proxies for the morphological and transport properties of the NPC. We show that in high-density FG nup assemblies, increase in cohesiveness leads to the decrease in their permeability, in accordance with the accepted view. On the other hand, the permeability of low-density assemblies is a nonmonotonic function of the cohesiveness, and a moderate increase in cohesiveness can enhance permeability. The density- and cohesiveness-dependent effects on permeability are explained by considering the free-energy cost associated with penetrating the FG nup assemblies. We discuss the implications of these findings for the organization and function of the NPC. 相似文献