bluuebunny/crossref_metadata_2025_split huggingface dataset:
Purification and Characterization of a Hemolysin-Like Protein, Sll1951, a Nontoxic Member of the RTX Protein Family from the Cyanobacterium
Synechocystis
sp. Strain PCC 6803
Authors: Sakiyama Tetsushi , Ueno Hironori , Homma Hideya , Numata Osamu , Kuwabara Tomohiko 
Published: May 2006

ABSTRACT

The hemolysin-like protein (HLP) Sll1951, characterized by the GGXGXDXUX nonapeptide motif implicated in Ca
2+
binding, was purified from the glucose-tolerant strain (GT) of
Synechocystis
sp. strain PCC 6803. HLP was eluted at 560 kDa after gel filtration chromatography. Atomic absorption spectroscopy indicated that the protein bound calcium. The bound Ca
2+
was not chelated with EGTA; however, it was released after being heated at 100°C for 1 min, and it rebound to the Ca
2+
-depleted protein at room temperature. The apparent HLP molecular mass increased to 1,000 kDa and reverted to 560 kDa during the release and rebinding of Ca
2+
, respectively. The monomers of the respective forms appeared at 90 and 200 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. HLP showed no apparent hemolytic activity against sheep erythrocytes; however, a slight hemolytic activity was detected during the conformational change caused by the rebinding of Ca
2+
. Immunoelectron microscopy using polyclonal antibodies against the 200-kDa monomer revealed that HLP is located in the cell surface layer. The localization and Ca
2+
-induced reversible conformational change suggest that HLP is a member of the repeat in toxin (RTX) protein family despite its latent and low toxicity. In some other cyanobacteria, RTX proteins are reported to be necessary for cell motility. However, the GT was immotile. Moreover, the motile wild-type strain did not express any HLP, suggesting that HLP is one of the factors involved in the elimination of motility in the GT. We concluded that the involvement of RTX protein in cyanobacterial cell motility is not a general feature.
Differential Proteomic Analysis of theBacillus anthracisSecretome: Distinct Plasmid and Chromosome CO2-Dependent Cross Talk Mechanisms Modulate Extracellular Proteolytic Activities
Authors: Chitlaru Theodor , Gat Orit , Gozlan Yael , Ariel Naomi , Shafferman Avigdor 
Published: May 2006

ABSTRACTThe secretomes of a virulentBacillus anthracisstrain and of avirulent strains (cured of the virulence plasmids pXO1 and pXO2), cultured in rich and minimal media, were studied by a comparative proteomic approach. More than 400 protein spots, representing the products of 64 genes, were identified, and a unique pattern of protein relative abundance with respect to the presence of the virulence plasmids was revealed. In minimal medium under high CO2tension, conditions considered to simulate those encountered in the host, the presence of the plasmids leads to enhanced expression of 12 chromosome-carried genes (10 of which could not be detected in the absence of the plasmids) in addition to expression of 5 pXO1-encoded proteins. Furthermore, under these conditions, the presence of the pXO1 and pXO2 plasmids leads to the repression of 14 chromosomal genes. On the other hand, in minimal aerobic medium not supplemented with CO2, the virulent and avirulentB. anthracisstrains manifest very similar protein signatures, and most strikingly, two proteins (the metalloproteases InhA1 and NprB, orthologs of gene products attributed to theBacillus cereusgroup PlcR regulon) represent over 90% of the total secretome. Interestingly, of the 64 identified gene products, at least 31 harbor features characteristic of virulence determinants (such as toxins, proteases, nucleotidases, sulfatases, transporters, and detoxification factors), 22 of which are differentially regulated in a plasmid-dependent manner. The nature and the expression patterns of proteins in the various secretomes suggest that distinct CO2-responsive chromosome- and plasmid-encoded regulatory factors modulate the secretion of potential novel virulence factors, most of which are associated with extracellular proteolytic activities.
Cation-Induced Transcriptional Regulation of the
dlt
Operon of
Staphylococcus aureus
Authors: Koprivnjak Tomaz , Mlakar Vid , Swanson Lindsey , Fournier Benedicte , Peschel Andreas , Weiss Jerrold P. 
Published: May 2006

ABSTRACT

Lipoteichoic and wall teichoic acids (TA) are highly anionic cell envelope-associated polymers containing repeating polyglycerol/ribitol phosphate moieties. Substitution of TA with
d
-alanine is important for modulation of many cell envelope-dependent processes, such as activity of autolytic enzymes, binding of divalent cations, and susceptibility to innate host defenses.
d
-Alanylation of TA is diminished when bacteria are grown in medium containing increased NaCl concentrations, but the effects of increased salt concentration on expression of the
dlt
operon encoding proteins mediating
d
-alanylation of TA are unknown. We demonstrate that
Staphylococcus aureus
transcriptionally represses
dlt
expression in response to high concentrations of Na
+
and moderate concentrations of Mg
2+
and Ca
2+
but not sucrose. Changes in
dlt
mRNA are induced within 15 min and sustained for several generations of growth. Mg
2+
-induced
dlt
repression depends on the ArlSR two-component system. Northern blotting, reverse transcription-PCR, and SMART-RACE analyses suggest that the
dlt
transcript begins 250 bp upstream of the
dltA
start codon and includes an open reading frame immediately upstream of
dltA
. Chloramphenicol transacetylase transcriptional fusions indicate that a region encompassing the 171 to 325 bp upstream of
dltA
is required for expression and Mg
2+
-induced repression of the
dlt
operon in
S. aureus
.
Living with Genome Instability: the Adaptation of Phytoplasmas to Diverse Environments of Their Insect and Plant Hosts
Authors: Bai Xiaodong , Zhang Jianhua , Ewing Adam , Miller Sally A. , Jancso Radek Agnes , Shevchenko Dmitriy V. , Tsukerman Kiryl , Walunas Theresa , Lapidus Alla , Campbell John W. , Hogenhout Saskia A. 
Published: May 2006

ABSTRACT

Phytoplasmas
(“
Candidatus
Phytoplasma,” class
Mollicutes
) cause disease in hundreds of economically
important plants and are obligately transmitted by sap-feeding insects
of the order Hemiptera, mainly leafhoppers and psyllids. The 706,569-bp
chromosome and four plasmids of aster yellows phytoplasma strain
witches' broom (AY-WB) were sequenced and compared to the onion yellows
phytoplasma strain M (OY-M) genome. The phytoplasmas have small
repeat-rich genomes. This comparative analysis revealed that the
repeated DNAs are organized into large clusters of potential mobile
units (PMUs), which contain
tra5
insertion
sequences (ISs) and genes for specialized sigma factors and membrane
proteins. So far, these PMUs appear to be unique to phytoplasmas.
Compared to mycoplasmas, phytoplasmas lack several recombination and
DNA modification functions, and therefore, phytoplasmas may use
different mechanisms of recombination, likely involving PMUs, for the
creation of variability, allowing phytoplasmas to adjust to the diverse
environments of plants and insects. The irregular GC skews and the
presence of ISs and large repeated sequences in the AY-WB and OY-M
genomes are indicative of high genomic plasticity. Nevertheless,
segments of ∼250 kb located between the
lplA
and
glnQ
genes are syntenic between the two phytoplasmas and
contain the majority of the metabolic genes and no ISs. AY-WB appears
to be further along in the reductive evolution process than OY-M. The
AY-WB genome is ∼154 kb smaller than the OY-M genome, primarily
as a result of fewer multicopy sequences, including PMUs. Furthermore,
AY-WB lacks genes that are truncated and are part of incomplete
pathways in OY-M.
Kinetics of α-chymotrypsin action. I. pH, solvent, and temperature effects
Authors: Kaplan Harvey , Laidler K. J. 
Published: May 2006

An investigation has been made of the influence of pH on the kinetics of the α-chymotrypsin-catalyzed hydrolysis of N-acetyl-l-tyrosine ethyl ester, p-nitrophenyl acetate, and N-benzoyl-d- and -l-alanine methyl esters. From the pH variations of [Formula: see text], and [Formula: see text], it is deduced that in the free enzyme there are ionizing groups of pK 6.9 and 9.2. From the variation of these pK values with dielectric constant, it is concluded that, when protonated, one group is cationic and the other neutral. A temperature-dependence study was carried out on N–benzoyl-d- and -l-alanine methyl esters. The sharp break in the plot of log [Formula: see text] against 1/T is attributed to a rapid reversible denaturation of the enzyme at the higher temperatures. In the low-temperature region, the activation energies are ΔEL = 16.2 ± 0.3 kcal/mole and ΔED = 16.5 ± 0.6 kcal/mole.
The radiolysis of ethanol. VI. Hydrogen precursors at −196°C
Authors: Fletcher J. W. , Freeman G. R. 
Published: May 2006

Reactions of trapped (or solvated) electrons in solid ethanol have been studied. The following reactions occur at − 196 °C. [Formula: see text] [Formula: see text] [Formula: see text]The activation energy of reaction [6] is roughly 5 kcal/mole. Reaction [7] occurs with electrons that have not yet been trapped by the medium.Hydrogen atoms appear to be able to abstract from ethanol and to add to propylene at − 196 °C.
Pulse radiolysis studies XI. Protonation reactions of aromatic anions in some aliphatic alcohols
Authors: Arai Shigeyoshi , Tremba E. L. , Brandon J. R. , Dorfman Leon M. 
Published: May 2006

The protonation reaction of aromatic anion radicals in the aliphatic alcohols, [Formula: see text]has been investigated by the pulse radiolysis method. Activation energies for this reaction have been determined for the anthracenide anion and diphenylide anion in methanol, ethanol, and isopropanol, and for the naphthalenide anion in isopropanol. Absolute rate constants have been determined as well for the phenanthrenide, o-terphenylide, and m-terphenylide anions in isopropanol at 25 °C. The values for the rate constants, activation energies, and the pre-exponential factors are given. Those properties of the system which determine the kinetics are briefly discussed.
Polarographic reduction of some Schiff bases in dimethylformamide
Authors: Scott John M. W. , Jura W. H. 
Published: May 2006

The half-wave potentials of a series of Schiff bases of the type [Formula: see text], where Ar and Ar′ are unsubstituted aryl groups, have been measured in dimethylformamide. The effect of structural variations of the aryl groups Ar and Ar′ on these potentials have been calculated by the linear combination of molecular orbitals (l.c.m.o.) variant of the Hückel molecular orbital (H.m.o.) theory without specific consideration of the nitrogen heteroatom present in these compounds. It is demonstrated that the equation which relates E1/2 for the first electron transfer to theoretical quantities calculated by the l.c.m.o. theory can be applied to the data in several ways, one of which shows an interesting analogy with the Hammett σ−ρ treatment of linear free energy relationships.
Mercury-photosensitized decomposition of dimethyl ether. Part II. The thermal decomposition of the methoxymethyl radical
Authors: Loucks Leon F. , Laidler Keith J. 
Published: May 2006

The decomposition of the methoxymethyl radical, generated in the mercury-photosensitized decomposition of dimethyl ether, has been investigated over the temperature range 200 to 300 °C and the pressure range 3 to 600 mm Hg. The radical decomposes to give a formaldehyde molecule and a methyl radical. The effects of pressure and temperature on the first-order rate coefficient for the decomposition of the methoxymethyl radical have been examined in detail. The rate coefficient shows a pressure dependence over the full pressure range studied. The order of the decomposition is about 1.4 at the middle of the pressure range studied, with a lower order at higher pressures and a higher order at lower pressures. At 100 mm Hg the observed activation energy for the decomposition of the methoxymethyl radical is 24.8 kcal/mole.The first-order and second-order rate coefficients, k∞ and k0, corresponding to the limiting conditions of high pressures and low pressures respectively, have been evaluated as [Formula: see text]Kassel integrations have been carried out for the methoxymethyl radical and have been fitted to the experimental data. It is concluded that 8 or 9 normal modes contribute to the energization of the radical. The rate coefficient is increased by the presence of carbon dioxide, but carbon dioxide has a lower efficiency than dimethyl ether for the transfer of energy in the energization process.
Copper(II)-catalyzed oxidation of carbon monoxide by molecular oxygen
Authors: Byerley J. J. , Lee Jolland Y. H. 
Published: May 2006

The kinetics of the copper (II)-catalyzed oxidation of carbon monoxide by molecular oxygen, i.e. [Formula: see text] have been investigated in aqueous solutions at 120 °C. The rate law was found to be of the form −d[O2]/dt = kexpt[O2][CO][Cu(II)]/[H+], where kexpt = 7.88 × 10−6 M−1 s−1 in 0.25 M acetate solutions. The apparent activation energy is 29 600 cal/mole. The rate-determining step of the reaction appears to be the oxidation by molecular oxygen of a carbon monoxide insertion complex [Formula: see text] formed in the pre-equilibrium step.
Sur quelques réactions acide–base dans les solvants fortement basiques anhydres. I. Éthylènediamine
Authors: Heumann W. R. , Bouchard A. , Tremblay G. 
Published: May 2006

The neutralization of 20 monobasic acids of various strength in anhydrous ethylenediamine was studied potentiometrically using a platinum indicating electrode. The base used was the solvent anion's lithium salt LiHNC2H4NH2. Potential jumps ranging from 1 300 mV for hydrochloric acid to 150 mV for diphenylmethane were obtained. The latter compound was the least acidic ( [Formula: see text]) to react with the base. By plotting the half-neutralization potentials against the [Formula: see text] values of the literature and extrapolating towards the potential obtained with the pure solvent, the [Formula: see text] of ethylenediamine was estimated as 38. The potentials of the pure acid solutions varied little from one acid to another, which corroborates the opinion that even strong electrolytes are little dissociated in ethylenediamine. The potentials at half-neutralization, however, were much more different. These facts suggest that in this solvent acid strength is not as directly related to the degree of dissociation as in aqueous solutions. The neutralization of several dibasic acids was also attempted. Some were found to be too insoluble, the others gave unusual curves, which are difficult to explain.La neutralisation de 20 acides monobasiques de différentes forces dans l'éthylènediamine anhydre a été étudiée par potentiométrie avec une électrode indicatrice de platine. La base utilisée était le sel de lithium de l'anion du solvant LiHNC2H4NH2. Les sauts de potentiel variaient entre 1 300 mV pour l'acide chlorhydrique et 150 mV pour le diphénylméthane, qui était le composé le moins acide ( [Formula: see text]) à réagir avec la base. Si on porte les potentiels mesurés à la demi-neutralisation en fonction des [Formula: see text] de la littérature et si on extrapole jusqu'au potentiel obtenu avec le solvant pur, on trouve une valeur de 38 pour le [Formula: see text] de l'éthylènediamine. Les potentiels obtenus avec les solutions des différents acides purs variaient peu entre eux, ce qui confirme l'opinion que même les électrolytes forts sont peu dissociés dans l'éthylènediamine. Cependant, les potentiels à la demi-neutralisation variaient beaucoup plus d'un acide à l'autre. Ces faits semblent indiquer que dans ce solvant la force des acides ne varie pas aussi directement avec le degré de dissociation que dans les solutions aqueuses. La neutralisation de plusieurs acides polybasiques a été essayée également. Plusieurs de ces acides n'étaient pas assez solubles et les autres donnaient des courbes particulières, qui ne sont pas faciles à interpréter.
Low frequency infrared spectral studies on some of the molecular addition compounds of tin(IV) halides with triphenylphosphine and triphenylarsine
Authors: Rivest Roland , Singh Surjit , Abraham C. 
Published: May 2006

Molecular addition compounds of tin tetrahalides with triphenylphosphine and triphenylarsine have been prepared. The analytical results show that triphenylphosphine forms both 1:2 ( [Formula: see text]) and 1:1 ( [Formula: see text]) adducts (L = ligand), whereas triphenylarsine forms only 1:2 adducts. The effect of addition of these ligands on the ν(Sn—X) (where X = Cl, Br) of the Lewis acids has been studied. In all cases, νd(Sn—X) have been found to shift to a lower frequency region on coordination. Tentative assignments for ν(Sn—Y) (where Y = P, As) have been discussed on the basis of the experimental results.Les complexes d'addition moléculaire de tetrahalogénures d'étain et la triphénylarsine et la triphénylphosphine ont été préparés. Les résultats analytiques indiquent que la triphénylphosphine forme deux sortes de complexes [Formula: see text] et [Formula: see text] (L est le ligand), tandis que la triphénylarsine ne forme qu'une sorte de complexes [Formula: see text]. L'effet de l'addition de ces ligands sur la fréquence ν(Sn—X) (où X = Cl ou Br) des acides de Lewis a été étudié. Dans chaque cas, νd(Sn—X) diminue à cause de la coordination. On discute aussi de l'attribution possible de certaines bandes à ν(Sn—Y) (où Y = P ou As).
Selective Toxicity of NSC73306 in MDR1-Positive Cells as a New Strategy to Circumvent Multidrug Resistance in Cancer
Authors: Ludwig Joseph A. , Szakács Gergely , Martin Scott E. , Chu Benjamin F. , Cardarelli Carol , Sauna Zuben E. , Caplen Natasha J. , Fales Henry M. , Ambudkar Suresh V. , Weinstein John N. , Gottesman Michael M. 
Published: May 2006

Abstract
ATP-binding cassette (ABC) proteins include the best known mediators of resistance to anticancer drugs. In particular, ABCB1 [MDR1/P-glycoprotein (P-gp)] extrudes many types of drugs from cancer cells, thereby conferring resistance to those agents. Attempts to overcome P-gp-mediated drug resistance using specific inhibitors of P-gp has had limited success and has faced many therapeutic challenges. As an alternative approach to using P-gp inhibitors, we characterize a thiosemicarbazone derivative (NSC73306) identified in a generic screen as a compound that exploits, rather than suppresses, P-gp function to induce cytotoxicity. Cytotoxic activity of NSC73306 was evaluated in vitro using human epidermoid, ovarian, and colon cancer cell lines expressing various levels of P-gp. Our findings suggest that cells become hypersensitive to NSC73306 in proportion to the increased P-gp function and multidrug resistance (MDR). Abrogation of both sensitivity to NSC73306 and resistance to P-gp substrate anticancer agents occurred with specific inhibition of P-gp function using either a P-gp inhibitor (PSC833, XR9576) or RNA interference, suggesting that cytotoxicity was linked to MDR1 function, not to other, nonspecific factors arising during the generation of resistant or transfected cells. Molecular characterization of cells selected for resistance to NSC73306 revealed loss of P-gp expression and consequent loss of the MDR phenotype. Although hypersensitivity to NSC73306 required functional expression of P-gp, biochemical assays revealed no direct interaction between NSC73306 and P-gp. This article shows that NSC73306 kills cells with intrinsic or acquired P-gp-induced MDR and indirectly acts to eliminate resistance to MDR1 substrates. (Cancer Res 2006; 66(9): 4808-15)
3,3′-Diindolylmethane Is a Novel Mitochondrial H+-ATP Synthase Inhibitor that Can Induce p21Cip1/Waf1 Expression by Induction of Oxidative Stress in Human Breast Cancer Cells
Authors: Gong Yixuan , Sohn Heesook , Xue Ling , Firestone Gary L. , Bjeldanes Leonard F. 
Published: May 2006

AbstractEpidemiologic evidence suggests that high dietary intake of Brassica vegetables, such as broccoli, cabbage, and Brussels sprouts, protects against tumorigenesis in multiple organs. 3,3′-Diindolylmethane, one of the active products derived from Brassica vegetables, is a promising antitumor agent. Previous studies in our laboratory showed that 3,3′-diindolylmethane induced a G1 cell cycle arrest in human breast cancer MCF-7 cells by a mechanism that included increased expression of p21. In the present study, the upstream events leading to p21 overexpression were further investigated. We show for the first time that 3,3′-diindolylmethane is a strong mitochondrial H+-ATPase inhibitor (IC50∼20 μmol/L). 3,3′-Diindolylmethane treatment induced hyperpolarization of mitochondrial inner membrane, decreased cellular ATP level, and significantly stimulated mitochondrial reactive oxygen species (ROS) production. ROS production, in turn, led to the activation of stress-activated pathways involving p38 and c-Jun NH2-terminal kinase. Using specific kinase inhibitors (SB203580 and SP600125), we showed the central role of p38 and c-Jun NH2-terminal kinase (JNK) pathways in 3,3′-diindolylmethane-induced p21 mRNA transcription. In addition, antioxidants significantly attenuated 3,3′-diindolylmethane-induced activation of p38 and JNK and induction of p21, indicating that oxidative stress is the major trigger of these events. To further support the role of ROS in 3,3′-diindolylmethane-induced p21 overexpression, we showed that 3,3′-diindolylmethane failed to induce p21 overexpression in mitochondrial respiratory chain deficient ρ0 MCF-7 cells, in which 3,3′-diindolylmethane did not stimulate ROS production. Thus, we have established the critical role of enhanced mitochondrial ROS release in 3,3′-diindolylmethane-induced p21 up-regulation in human breast cancer cells. (Cancer Res 2006; 66(9): 4880-7)
Identification and properties of proteases from an Acanthamoeba isolate capable of producing granulomatous encephalitis
Authors: Sissons James , Alsam Selwa , Goldsworthy Graham , Lightfoot Mary , Jarroll Edward L , Khan Naveed Ahmed 
Published: May 2006

Abstract

Background
Granulomatous amoebic encephalitis due to Acanthamoeba is often a fatal human disease. However, the pathogenesis and pathophysiology of Acanthamoeba encephalitis remain unclear. In this study, the role of extracellular Acanthamoeba proteases in central nervous system pathogenesis and pathophysiology was examined.

Results
Using an encephalitis isolate belonging to T1 genotype, we observed two major proteases with approximate molecular weights of 150 KD and 130 KD on SDS-PAGE gels using gelatin as substrate. The 130 KD protease was inhibited with phenylmethylsulfonyl fluoride (PMSF) suggesting that it is a serine protease, while the 150 KD protease was inhibited with 1, 10-phenanthroline suggesting that it is a metalloprotease. Both proteases exhibited maximal activity at neutral pH and over a range of temperatures, indicating their physiological relevance. These proteases degrade extracellular matrix (ECM), which provide structural and functional support to the brain tissue, as shown by the degradation of collagen I and III (major components of collagenous ECM), elastin (elastic fibrils of ECM), plasminogen (involved in proteolytic degradation of ECM), as well as casein and haemoglobin. The proteases were purified partially using ion-exchange chromatography and their effects were tested in an in vitro model of the blood-brain barrier using human brain microvascular endothelial cells (HBMEC). Neither the serine nor the metalloprotease exhibited HBMEC cytotoxicity. However, the serine protease exhibited HBMEC monolayer disruptions (trypsin-like) suggesting a role in blood-brain barrier perturbations.

Conclusion
Overall, these data suggest that Acanthamoeba proteases digest ECM, which may play crucial role(s) in invasion of the brain tissue by amoebae.