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991.
GAPs for rho-related GTPases 总被引:26,自引:0,他引:26
Ras-related GTP-binding proteins (GTPases) of the rbo subfamily play important roles in regulating the organization of the actin cytoskeleton. A large number of multifunctional proteins that can stimulate their intrinsic GTPase activity have been identified. Here, we discuss the nature of such GTPase-activating proteins (GAPs) and their potential importance for cell signalling. 相似文献
992.
Michael Steinert Manfred Ott P. Christian Lück Egbert Tannich Jörg Hacker 《FEMS microbiology ecology》1994,15(3-4):299-308
Abstract Legionella pneumophila strains isolated from different sources were tested for their host range in the protists Acanthamoeba castellanii, Hartmannella vermiformis and Entamoeba histolytica . It has been shown that A. castellanii and H. vermiformis but not E. histolytica support the intracellular replication of L. pneumophila . Furthermore it could be demonstrated that in vivo virulence in the guinea pig and the intracellular growth in U937 cells coincides with the capability to replicate intracellularly in A. castellanii at 37°C. The infectivity of L. pneumophila that had sustained a 48 hours nutrient deprivation was not significantly different from that of legionellae grown to log-phase on BCYE plates. In contrast the nutrient limitation on A. castellanii increased the amount of intracellular legionellae at the beginning of infection. An initial opsonin independent attachement stage of legionellae to U937 cells was demonstrated by scanning electron microscopy. In contrast, L. pneumophila's capability of stable or long term attachmennt to A. castellanii was shown to be inefficient. 相似文献
993.
Abstract A dense population of the purple sulfur bacterium Amoebobacter purpureus in the chemocline of meromictic Mahoney Lake (British Columbia, Canada) underwent consistent changes in biomass over a two year study period. The integrated amount of bacteriochlorophyll reached maxima in August and declined markedly during early fall. Bacteriochlorophyll was only weakly correlated with the light intensity and water temperature in the chemocline. In the summer, bacterial photosynthesis was limited by sulfide availability. During this period the intracellular sulfur concentration of A. purpureus cells decreased. A minimum concentration was measured at the top of the bacterial layer in August, when specific photosynthetic rates of A. purpureus indicated that only 14% of the cells were photosynthetically active. With the exception of a time period between August and September, the specific growth rates calculated from CO2 fixation rates of A. purpureus were similar to growth rates calculated from actual biomass changes in the bacterial layer. Between August and September 86% of the A. purpureus biomass disappeared from the chemocline and were deposited on the littoral sediment of Mahoney Lake or degraded within the mixolimnion. This rise of cells to the lake surface was not mediated by an increase in the specific gas vesicle content which remained constant between April and November. The upwelling phenomenon was related to the low sulfur content of A. purpureus cells and a low resistance of surface water layers against vertical mixing by wind. 相似文献
994.
Michael Mesterton-Gibbons 《Evolutionary ecology》1994,8(3):230-247
Summary The classic Hawk—Dove game is extended to deal with continuous variation in resource-holding potential or RHP, when RHP is observable (via any sensory modality) but RHP difference is less than perfectly reliable as a predictor of the outcome of an escalated contest. The relationship between sensory and physical magnitudes of RHP is assumed to be governed by Fechner's psychophysical law, whose effect is that contestants interact as if they had perfect information about their relative RHP (as opposed to RHP difference). Thus, an animal is aggressive if its RHP exceeds a certain fraction, called its threshold, of its opponent's RHP and otherwise is non-aggressive; and the classic Hawk and Dove strategies correspond to zero and infinite thresholds, respectively. For RHPs drawn at random from an arbitrary Gamma distribution there is a unique evolutionarily stable strategy or ESS, which depends on a parameter measuring the reliability of RHP as a predictor of the outcome of a fight, on the ratio of the valueV of winning to the costC of losing (both measured in units of reproductive fitness) and on the mean µ and variance 2 of the RHP distribution. In a population at this ESS, ifV/C < 1 then the threshold is 1 and there is no fighting. AsV/C increases beyond 1 to a second critical value , however, the threshold decreases steadily from 1 to 0 and remains 0 forV/C > ; is an increasing function of , but a decreasing function of 2. That a lower variance of RHP can imply a lower escalation frequencyp is a novel insight of the analysis. The prediction is at first counterintuitive, because if the aggression threshold were fixed then larger variance would imply lowerp (dispersion effect of variance). When natural selection acts on the threshold, however, increasing the variance not only reduces the probability that an animal with larger RHP will be attacked by an animal with lower RHP at the existing threshold, but also reduces the expected costs of adopting that particular threshold, so that a mutant with a somewhat lower threshold can invade the population (selection effect of variance). Forp, the selection effect dominates toward the upper end of the interval 1 V/C . 相似文献
995.
996.
Summary 1. We examined the actions of mercury (Hg2+) and zinc (Zn2+) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg2+ and Zn2+. The threshold concentration for Hg2+ effects was 0.1 µM and that for Zn2+ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg2+ or 200µM Zn2+. The peak calcium current was reduced to 50% (IC50) by 1.1µM Hg2+ or 69µM Zn2+. While Zn2+ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg2+ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn2+ was not dependent on an open channel state, Hg2+ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg2+ and with higher concentrations (>100µM) of Zn2+.5. As Zn2+ in the concentration range used had no influence on resting membrane currents, Hg2+ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects. 相似文献
997.
Marcelo V. Sousa Michael Richardson Wagner Fontes Lauro Morhy 《Journal of Protein Chemistry》1994,13(8):659-667
Enterolobin, a 55-kDa cytolytic, inflammatory, and insecticidal protein isolated from seeds of the Brazilian treeEnterolobium contortisiliquum (Leguminosae-Mimosoideae) has been further purified and partially sequenced by using both manual and automated methods. A computational search of enterolobin partial amino acid sequence against the PIR database revealed possible sequence similarities with aerolysins, cytolytic proteins fromAeromonas species. An alignment of enterolobin partial sequence to the amino acid sequences ofA. hydrophila andA. sobria aerolysins showed several similar regions with many residue identites. The seed protein enterolobin and the bacterial aerolysins may be homologous proteins despite the distant phylogenetic relationship. 相似文献
998.
James S. C. Gilchrist Michael P. Czubryt Grant N. Pierce 《Molecular and cellular biochemistry》1994,135(1):79-88
Calcium has long been known to play a role as a key cytoplasmic second messenger, but until relatively recently its possible involvement in nuclear signal transduction and the regulation of nuclear events has not been extensively studied. Evidence revealing the presence of transmembrane nuclear Ca2+ gradients and a variety of intranuclear Ca2+ binding proteins has fueled renewed interest in this key ion and its involvement in cell-cycle timing and division, gene expression, and protein activation. This review will offer an overview of the current state of knowledge and theory regarding calcium orchestration of nuclear functions and events and discuss possible future directions in this field of study. 相似文献
999.
Richard Wales Hazel C. Gorham Khalid Hussain Lynne M. Roberts J. Michael Lord 《Glycoconjugate journal》1994,11(4):274-281
Deleted forms of ricin B chain (RTB) containing only one of the two galactose binding sites were produced inE. coli and targeted to the periplasm by fusion to theompA orompF signal sequences. The proteins were then isolated from the periplasm and their sugar binding properties assessed. Previous studies investigating the properties of such proteins produced inXenopus laevis oocytes suggested that deleted forms of RTB, when not glycosylated, retain their ability to bind simple sugars, unlike the full-length unglycosylated proteins. When produced inE. coli however we found that only one, EB733, of a number of deleted forms of RTB closely related to those previously produced inXenopus laevis oocytes, bound to simple sugars. All of the deletion forms of RTB were found to bind in the asialofetuin binding assay; an assay which has been previously utilized to measure binding of lectins to the terminal galactose residues of glycoprotein oligosaccharides. However, in contrast to glycosylated RTB, binding of the deletion mutants could be competed to only a small degree or not at all with galactose. The only deletion mutant observed to bind to free galactose when produced inE. coli corresponded closely to the complete domain 2 of RTB. It is assumed that this mutant forms a stable structure similar to that of the C-terminal domain in the full-length protein. The structural integrity of EB733 was not only suggested by its sugar binding properties and solubility but also by its consistently higher level of expression and the absence of any apparent susceptibility toE. coli proteases.Abbreviations RTA
ricin toxin A chain
- RTB
ricin toxin B chain
- ER
endoplasmic reticulum
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
- IPTG
isopropyl -d-thiogalactopyranoside 相似文献
1000.