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131.
Two unicellular cyanobacteria Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 showed contrasting responses to chromate stress with EC50 of 12 ± 2 and 150 ± 15 μM potassium dichromate respectively. There was no depletion of chromate in growth medium in both the cases. Using labeled chromate, very low accumulation (<1 nmol/108 cells) was observed in Synechocystis after incubation for 24 h in light. No accumulation of chromate could be observed in Synechococcus under these conditions. Chromate oxyanion is known to enter the cells using sulfate uptake channels. Therefore, inhibition of sulfate uptake caused by chromate was monitored using 35S labeled sulfate. IC50 values of chromate for 35sulfate uptake were higher in Synechococcus as compared to Synechocystis. The results suggested that the sulfate transporters in Synechococcus have lower affinity to chromate than those from Synechocystis possibly due to differences in affinity of sulfate receptors for chromate. Bioinformatic analyses revealed presence of sulfate and chromate transporters with considerable similarity; however, minor differences in these may play a role in their differential response to chromate. In both cases the IC50 values decreased when sulfate concentration was reduced in the medium indicating competitive inhibition of sulfate uptake by chromate. Interestingly, Synechococcus showed stimulation of growth at concentrations of chromate less than 100 μM, which affected its cell size without disturbing the ultrastructure and thylakoid organization. In Synechocystis, growth with 12 μM potassium dichromate damaged the ultrastructure and thylakoid organization with slight elongation of the cells. The results suggested that Synechococcus possesses efficient strategies to prevent entry and to remove chromate from the cell as compared to Synechocystis. This is the first time a differential response of Synechococcus 7942 and Synechocystis 6803 to chromate is reported. The contrasting characteristics observed in the two cyanobacteria will be useful in understanding the basis of resistance or susceptibility to chromate. 相似文献
132.
Kaur Harsimran Shankarnarayana Shamanth A. Hallur Vinaykumar Muralidharan Jayashree Biswal Manisha Ghosh Anup K. Ray Pallab Chakrabarti Arunaloke Rudramurthy Shivaprakash M. 《Mycopathologia》2020,185(2):257-268
Mycopathologia - A sudden rise of Candida krusei candidemia cases was noticed in our hospital within 1 year with maximum cases from paediatric unit. The present study reports the results... 相似文献
133.
Background and Scope
In eukaryotes, chromatin remodelling complexes are shown to be responsible for nucleosome mobility, leading to increased accessibility of DNA for DNA binding proteins. Although the existence of such complexes in plants has been surmised mainly at the genetic level from bioinformatics studies and analysis of mutants, the biochemical existence of such complexes has remained unexplored.Methods
Histone H1-depleted donor chromatin was prepared by micrococcal nuclease digestion of wheat nuclei and fractionation by exclusion chromatography. Nuclear extract was partially purified by cellulose phosphate ion exchange chromatography. Histone octamer trans-transfer activity was analysed using the synthetic nucleosome positioning sequence in the absence and presence of ATP and its analogues. ATPase activity was measured as 32Pi released using liquid scintillation counting.Key Results
ATP-dependent histone octamer trans-transfer activity, partially purified from wheat nuclei using cellulose phosphate, showed ATP-dependent octamer displacement in trans from the H1-depleted native donor chromatin of wheat to the labelled synthetic nucleosome positioning sequence. It also showed nucleosome-dependent ATPase activity. Substitution of ATP by ATP analogues, namely ATPγS, AMP-PNP and ADP abolished the octamer trans-transfer, indicating the requirement of ATP hydrolysis for this activity.Conclusions
ATP-dependent histone octamer transfer in trans is a recognized activity of chromatin remodelling complexes required for chromatin structure dynamics in non-plant species. Our results suggested that wheat nuclei also possess a typical chromatin remodelling activity, similar to that in other eukaryotes. This is the first report on chromatin remodelling activity in vitro from plants. 相似文献134.
His(E7) to Trp replacements in HbA lead to markedly biphasic bimolecular CO rebinding after laser photolysis. For isolated mutant subunits, the fraction of fast phase increases with increasing [CO], suggesting a competition between binding to an open conformation with an empty E7 channel and relaxation to blocked or closed, slowly reacting states. The rate of conformational relaxation of the open state is ~18,000 s(-1) in α subunits and ~10-fold faster in β subunits, ~175,000 s(-1). Crystal structures were determined for tetrameric α(WT)β(Trp-63) HbCO, α(Trp-58)β(WT) deoxyHb, and Trp-64 deoxy- and CO-Mb as controls. In Trp-63(E7) βCO, the indole side chain is located in the solvent interface, blocking entry into the E7 channel. Similar blocked Trp-64(E7) conformations are observed in the mutant Mb crystal structures. In Trp-58(E7) deoxy-α subunits, the indole side chain fills both the channel and the distal pocket, forming a completely closed state. The bimolecular rate constant for CO binding, k'(CO), to the open conformations of both mutant Hb subunits is ~80-90 μm(-1) s(-1), whereas k'(CO) for the completely closed states is 1000-fold slower, ~0.08 μm(-1) s(-1). A transient intermediate with k'(CO) ≈ 0.7 μm(-1) s(-1) is observed after photolysis of Trp-63(E7) βCO subunits and indicates that the indole ring blocks the entrance to the E7 channel, as observed in the crystal structures of Trp(E7) deoxyMb and βCO subunits. Thus, either blocking or completely filling the E7 channel dramatically slows bimolecular binding, providing strong evidence that the E7 channel is the major pathway (≥90%) for ligand entry in human hemoglobin. 相似文献
135.
136.
Wiener JJ Gomez L Venkatesan H Santillán A Allison BD Schwarz KL Shinde S Tang L Hack MD Morrow BJ Motley ST Goldschmidt RM Shaw KJ Jones TK Grice CA 《Bioorganic & medicinal chemistry letters》2007,17(10):2718-2722
We have previously reported a novel class of tetrahydroindazoles that display potency against a variety of Gram-positive and Gram-negative bacteria, potentially via interaction with type II bacterial topoisomerases. Herein are reported SAR investigations of this new series. Several compounds possessing broad-spectrum potency were prepared. Further, these compounds exhibit activity against multidrug-resistant Gram-positive microorganisms equivalent to that against susceptible strains. 相似文献
137.
Mutations that inactivate either merlin (mer) or expanded (ex) result in increased cell growth and proliferation in Drosophila. Both Mer and Ex are members of the Band 4.1 protein superfamily, and, based on analyses of mer ex double mutants, they are proposed to function together in at least a partially redundant manner upstream of the Hippo (Hpo) and Warts (Wts) proteins to regulate cell growth and division. By individually analyzing ex and mer mutant phenotypes, we have found important qualitative and quantitative differences in the ways Mer and Ex function to regulate cell proliferation and cell survival. Though both mer and ex restrict cell and tissue growth, ex clones exhibit delayed cell cycle exit in the developing eye, while mer clones do not. Conversely, loss of mer substantially compromises normal developmental apoptosis in the pupal retina, while loss of ex has only mild effects. Finally, ex has a role in regulating Wingless protein levels in the eye that is not obviously shared by either mer or hpo. Taken together, our data suggest that Mer and Ex differentially regulate multiple downstream pathways. 相似文献
138.
Regulation of Fc?RI Signaling in Mast Cells by G Protein-coupled Receptor Kinase 2 and Its RH Domain
Hariharan Subramanian Kshitij Gupta Narayanan Parameswaran Hydar Ali 《The Journal of biological chemistry》2014,289(30):20917-20927
Agonist-induced phosphorylation of G protein-coupled receptors (GPCRs) by GPCR kinases (GRKs) promotes their desensitization and internalization. Here, we sought to determine the role of GRK2 on FcϵRI signaling and mediator release in mast cells. The strategies utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2flox/flox/cre recombinase) and overexpression of GRK2 and its regulator of G protein signaling homology (RH) domain (GRK2-RH). We found that silencing GRK2 expression caused ∼50% decrease in antigen-induced Ca2+ mobilization and degranulation but resulted in ablation of cytokine (IL-6 and IL-13) generation. The effect of GRK2 on cytokine generation does not require its catalytic activity but is mediated via the phosphorylation of p38 and Akt. Overexpression of GRK2 or its RH domain (GRK2-RH) enhanced antigen-induced mast cell degranulation and cytokine generation without affecting the expression levels of any of the FcϵRI subunits (α, β, and γ). GRK2 or GRK2-RH had no effect on antigen-induced phosphorylation of FcϵRIγ or Src but enhanced tyrosine phosphorylation of Syk. These data demonstrate that GRK2 modulates FcϵRI signaling in mast cells via at least two mechanisms. One involves GRK2-RH and modulates tyrosine phosphorylation of Syk, and the other is mediated via the phosphorylation of p38 and Akt. 相似文献
139.
In this paper, we have applied an efficient wavelet-based approximation method for solving the Fisher’s type and the fractional Fisher’s type equations arising in biological sciences. To the best of our knowledge, until now there is no rigorous wavelet solution has been addressed for the Fisher’s and fractional Fisher’s equations. The highest derivative in the differential equation is expanded into Legendre series; this approximation is integrated while the boundary conditions are applied using integration constants. With the help of Legendre wavelets operational matrices, the Fisher’s equation and the fractional Fisher’s equation are converted into a system of algebraic equations. Block-pulse functions are used to investigate the Legendre wavelets coefficient vectors of nonlinear terms. The convergence of the proposed methods is proved. Finally, we have given some numerical examples to demonstrate the validity and applicability of the method. 相似文献
140.
Michael Brad Strader Wayne A. Hicks Tigist Kassa Eileen Singleton Jayashree Soman John S. Olson Mitchell J. Weiss Todd L. Mollan Michael T. Wilson Abdu I. Alayash 《The Journal of biological chemistry》2014,289(32):22342-22357
A pathogenic V67M mutation occurs at the E11 helical position within the heme
pockets of variant human fetal and adult hemoglobins (Hb). Subsequent
post-translational modification of Met to Asp was reported in γ subunits
of human fetal Hb Toms River (γ67(E11)Val → Met) and β
subunits of adult Hb (HbA) Bristol-Alesha (β67(E11)Val → Met) that
were associated with hemolytic anemia. Using kinetic, proteomic, and crystal
structural analysis, we were able to show that the Met → Asp
transformation involves heme cycling through its oxoferryl state in the
recombinant versions of both proteins. The conversion to Met and Asp enhanced
the spontaneous autoxidation of the mutants relative to wild-type HbA and human
fetal Hb, and the levels of Asp were elevated with increasing levels of hydrogen
peroxide (H2O2). Using
H218O2, we verified incorporation of
18O into the Asp carboxyl side chain confirming the role of
H2O2 in the oxidation of the Met side chain. Under
similar experimental conditions, there was no conversion to Asp at the
αMet(E11) position in the corresponding HbA Evans (α62(E11)Val
→ Met). The crystal structures of the three recombinant Met(E11) mutants
revealed similar thioether side chain orientations. However, as in the solution
experiments, autoxidation of the Hb mutant crystals leads to electron density
maps indicative of Asp(E11) formation in β subunits but not in α
subunits. This novel post-translational modification highlights the
nonequivalence of human Hb α, β, and γ subunits with
respect to redox reactivity and may have direct implications to
α/β hemoglobinopathies and design of oxidatively stable Hb-based
oxygen therapeutics. 相似文献