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321.
Kenniston JA Burton RE Siddiqui SM Baker TA Sauer RT 《Journal of structural biology》2004,146(1-2):130-140
ClpX and related AAA+ ATPases of the Clp/Hsp100 family are able to denature native proteins. Here, we explore the role of protein stability in ClpX denaturation and subsequent ClpP degradation of model substrates bearing ssrA degradation tags at different positions. ClpXP degraded T. thermophilus RNase-H* with a C-terminal ssrA tag very efficiently, despite the very high global stability of this thermophilic protein. In fact, global thermodynamic stability appears to play little role in susceptibility to degradation, as a far less stable RNase-H*-ssrA mutant was degraded more slowly than wild type by ClpXP and a completely unfolded mutant variant was degraded less than twice as fast as the wild-type parent. When ssrA peptide tags were covalently linked to surface cysteines at positions 114 or 140 of RNase-H*, the conjugates were proteolyzed very slowly. This resistance to degradation was not caused by inaccessibility of the ssrA tag or an inability of ClpXP to degrade proteins with side-chain linked ssrA tags. Our results support a model in which ClpX denatures proteins by initially unfolding structural elements attached to the degradation tag, suggest an important role for the position of the degradation tag and direction of force application, and correlate well with the mapping of local protein stability within RNase-H* by native-state hydrogen exchange. 相似文献
322.
Cougnon M Benammou S Brouillard F Hulin P Planelles G 《American journal of physiology. Cell physiology》2002,282(6):C1445-C1453
To investigate theeffects of reactive oxygen species (ROS) on NH permeation in Xenopus laevis oocytes, we used intracellulardouble-barreled microelectrodes to monitor the changes in membranepotential (Vm) and intracellular pH(pHi) induced by a 20 mM NH4Cl-containingsolution. Under control conditions, NH4Cl exposure induceda large membrane depolarization (to Vm = 4.0 ± 1.5 mV; n = 21) and intracellularacidification [reaching a change in pHi(pHi) of 0.59 ± 0.06 pH units in 12 min]; theinitial rate of cell acidification (dpHi/dt) was0.06 ± 0.01 pH units/min. Incubation of the oocytes in thepresence of H2O2 or -amyloid protein had nomarked effect on the NH4Cl-induced pHi. Bycontrast, in the presence of photoactivated rose bengal (RB),tert-butyl-hydroxyperoxide (t-BHP), orxanthine/xanthine oxidase (X/XO), the same experimental maneuverinduced significantly greater pHi anddpHi/dt. These increases in pHiand dpHi/dt were prevented by the ROS scavengershistidine and desferrioxamine, suggesting involvement of the reactivespecies 1gO2 and ·OH. Using thevoltage-clamp technique to identify the mechanism underlying theROS-measured effects, we found that RB induced a large increase in theoocyte membrane conductance (Gm). ThisRB-induced Gm increase was prevented by 1 mMdiphenylamine-2-carboxylate (DPC) and by a low Na+concentration in the bath. We conclude that RB, t-BHP, andX/XO enhance NH influx into the oocyte via activationof a DPC-sensitive nonselective cation conductance pathway. 相似文献
323.
Jennifer C. Wilson Milton J. Kiefel Samia Albouz-Abo Mark von Itzstein 《Bioorganic & medicinal chemistry letters》2000,10(24)
1H NMR spectroscopy has been used to investigate the transfer of sialic acid from sialic acid donor molecules to acceptor molecules using the trans-sialidase from Typanosoma cruzi. It is clearly demonstrated that NMR spectroscopy is an efficient and powerful means of monitoring the trans-sialidase promoted transfer of sialic acid from donor to acceptor. 相似文献
324.
Ben Salem Nesrine Boussetta Sami de Rojas Itziar Moreno-Grau Sonia Montrreal Laura Mokni Narjes Mahmoud Imene Younes Samia Daouassi Nizar Frih-Ayed Mahbouba Hammami Afef Ben Ammar Elgaaied Amel Ruiz Agustín Cherni Lotfi 《Molecular biology reports》2022,49(3):1687-1700
Molecular Biology Reports - Alzheimer’s disease (AD) is the most common neurodegenerative disorder in humans and presents a major health problem throughout the world. The etiology of AD is... 相似文献
325.
Roselyne Defay Monique E. Astruc Samia Roussillon Bernard Descomps André Crastes de Paulet 《Biochemical and biophysical research communications》1982,106(2):362-372
The effects of a series of oxygenated sterols on DNA synthesis and HMG-CoA reductase activity were tested in human lymphocytes. The cells were stimulated by PHA and cultured in cholesterol containing medium. The inhibitory effects of sterols on DNA synthesis were strictly related to the position and the configuration of the hydroxyl on the side chain, to the side chain conformation and integrity and to the structure of the sterol nucleus. The inhibition of HMG-CoA reductase activity was less dependent on these structural features since all the sterols tested were strong inhibitors. In our experimental conditions the inhibition of DNA synthesis was not related to the suppression of the HMG CoA reductase activity. The specificity of the structures required for DNA synthesis inhibition could be explained by the involvement of a specific hydroxysterol binding protein. 相似文献
326.
Silvana Ciccotosto Milton J Kiefel Samia Abo Wendy Stewart Kaylene Quelch Mark von Itzstein 《Glycoconjugate journal》1998,15(7):663-669
The synthesis of 2-S-(2-aminoethyl) 5-acetamido-3,5-dideoxy-2-thio-D-glycero--D-galacto-2-nonulopyranosidon ic acid (1) has been successfully achieved from the precursors methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-S-acetyl-3,5-dideoxy-2-thio-D-glycero--D-galacto-2-nonulopyranosonate (2) and 2-bromo-N-(tert-butoxycarbonyl)-ethylamine (5). Compounds 1 and 2 were coupled, via amino and thioglycosidic linkages, respectively, to epoxy-activated Sepharose 6B. The resultant affinity adsorbents have proved efficient in purifying the sialic acid-recognizing enzyme Vibrio cholerae sialidase, in a one-step process with yields in the order of 60%. 相似文献
327.
The COE/EBF gene family marks a subset of prospective neurons in the vertebrate central and peripheral nervous system, including neurons deriving from some ectodermal placodes. Since placodes are often considered unique to vertebrates, we have characterised an amphioxus COE/EBF gene with the aim of using it as a marker to examine the timing and location of peripheral neuron differentiation. A single COE/EBF family member, AmphiCoe, was isolated from the amphioxus Branchiostoma floridae. AmphiCoe lies basal to the vertebrate COE/EBF genes in molecular phylogenetic analysis, suggesting that the duplications that formed the vertebrate COE/EBF family were specific to the vertebrate lineage. AmphiCoe is expressed in the central nervous system and in a small number of scattered ectodermal cells on the flanks of neurulae stage embryos. These cells become at least largely recessed beneath the ectoderm. Scanning electron microscopy was used to examine embryos in which the ectoderm had been partially peeled away. This revealed that these cells have neuronal morphology, and we infer that they are the precursors of epidermal primary sensory neurons. These characters lead us to suggest that differentiation of some ectodermal cells into sensory neurons with a tendency to sink beneath the embryonic surface represents a primitive feature that has become incorporated into placodes during vertebrate evolution. 相似文献
328.
Proteins interact with different partners to perform different functions and it is important to elucidate the determinants of partner specificity in protein complex formation. Although methods for detecting specificity determining positions have been developed previously, direct experimental evidence for these amino acid residues is scarce, and the lack of information has prevented further computational studies. In this article, we constructed a dataset that is likely to exhibit specificity in protein complex formation, based on available crystal structures and several intuitive ideas about interaction profiles and functional subclasses. We then defined a “structure‐based specificity determining position (sbSDP)” as a set of equivalent residues in a protein family showing a large variation in their interaction energy with different partners. We investigated sequence and structural features of sbSDPs and demonstrated that their amino acid propensities significantly differed from those of other interacting residues and that the importance of many of these residues for determining specificity had been verified experimentally. Proteins 2012;. © 2012 Wiley Periodicals, Inc. 相似文献
329.
Urbonavicius J Stahl G Durand JM Ben Salem SN Qian Q Farabaugh PJ Björk GR 《RNA (New York, N.Y.)》2003,9(6):760-768
Using mutants (tgt, mnmA(asuE, trmU), mnmE(trmE), miaA, miaB, miaE, truA(hisT), truB) of either Escherichia coli or Salmonella enterica serovar Typhimurium and the trm5 mutant of Saccharomyces cerevisiae, we have analyzed the influence by the modified nucleosides Q34, mnm(5)s(2)U34, ms(2)io(6)A37, Psi39, Psi55, m(1)G37, and yW37 on -1 frameshifts errors at various heptameric sequences, at which at least one codon is decoded by tRNAs having these modified nucleosides. The frequency of -1 frameshifting was the same in congenic strains only differing in the allelic state of the various tRNA modification genes. In fact, in one case (deficiency of mnm(5)s(2)U34), we observed a reduced ability of the undermodified tRNA to make a -1 frameshift error. These results are in sharp contrast to earlier observations that tRNA modification prevents +1 frameshifting suggesting that the mechanisms by which -1 and +1 frameshift errors occur are different. Possible mechanisms explaining these results are discussed. 相似文献
330.
With a view to clarify the induction of the "Crabtree consequence" in liver cells of S. mansoni infected mice, the curative effect of oil extract of C. longa was tested and compared to praziquantel (PZQ) the effective drug against all schistosome species occurring in man. Protein, glucose, glucose-6-phopsphatase, AMP-deaminase, adensoine deaminase, urea concentration, pyravate kinase (PK), phosphoenol pyruvate carboxykinase (PEPCK) and PK/PEPCK ratio were estimated. In addition, worm burden and ova count in mice infected with S. mansoni were elucidated. The result showed that C. longa normalized the concentration of protein, glucose, AMP-deaminase and adenosine deaminase, which were changed by infection. Moreover, it lowered pyruvate kinase level, while PZQ-treatment induced more elevation of this enzyme. PZQ was more effective in lowering worm burden while C. longa extract was more potent in reducing egg count. 相似文献