Search

Results show that the cellular microcystin content of Microcystis strain PCC 7806 varies between 34.5 and 81.4 fg per cell, which is positively correlated with growth rate under photosynthetically active radiation-limited growth. Data indicate a positive effect of light on microcystin production during and up to the maximum growth rate with hihger irradiances causing inhibition.

Research shows that the regulatable chromosomal suicide module, mazEF, is made of MazF stable toxin and MazE unstable antitoxin. Results indicate that mazEF mediated cell death is activated by thymine starvation by a severe reduction in the activity of the mazEF promoter P(sub)2.

Research has been conducted on Vibrio cholerae CTXphi, a filamentous bacteriophage encoding cholera toxin. The role of CTXphi minor coat protein in CTXphi infection has been ivestigated, and the results are reported.

Research has been conducted on mimosine, a toxin present in tree-legume leucaena. Results demonstrate that leucaena-nodulating Rhizobium sp. strain TAL1145 degrades mimosine and that the mid genes from the TAL1145 fragment are required for mimosine degradation to HP.

Results indicate that maintaining endogenous calcium homeostasis is important for the biosynthesis of cercosporin toxin in Cercospora nicotianae. Further, the calcium/calmodulin signal transduction is crucial for cercosporin biosynthesis as determined by number of pharamcological inhibitors of calcium/calmodulin regulation.

The authors discuss their research on plasmid toxin-antitoxin systems which kill daughter cells. The topics of interest include the ability of Escherichia coli toxin to cleave mRNA in the ribosomal A site in order to make it function as stress regulator during amino acid starvation.

Research has been conducted on differential gene expression in prokaryote cell population. Results demonstrate that differential expression is established at the transcription level.

Research has been conducted on Actinobacillus actinomycetemcomitans serotype b clone. The physiology of this high-toxic clone has been investigated, and the results demonstrate that none of the examined strains can utilize human transferrin as an iron source.

The authors review publications on enterohaemorrhagic Escherichia coli control. The topics of interest include the host responses to enterohaemorrhagic E. coli infection and the factors mediating enterohaemorrhagic E. coli intestinal interactions and survival in cattle and sheep.

Research has been conducted on virulence gene acquisition. The authors report that Vibrio cholerae encoded by neuraminidase (nanH) increases host cell sensitivity, and suggest that nanH has been acquired by horizontal gene transfer.

The effects of the scorpion [Alpha]-toxins Lqh II, Lqh III, and Lqh[Alpha]IT on human cardiac sodium channels (hH1), which were expressed in human embryonic kidney (HEK) 293 cells, were investigated. The toxins removed fast inactivation with [EC.sub.50] values of [is less than] 2.5 nM (Lqh III), 12 nM (Lqh II), and 33 nM (Lqh[Alpha]IT). Association and dissociation rates of Lqh III were much slower than those of Lqh II and Lqh[Alpha]IT, such that Lqh III would not dissociate from the channel during a cardiac activation potential. The voltage dependence of toxin dissociation from hH1 channels was nearly the same for all toxins tested, but it was different from that found for skeletal muscle sodium channels ([micro]I; Chen et al., 2000). These results indicate that the voltage dependence of toxin binding is a property of the channel protein. Toxin dissociation remained voltage dependent even at high voltages where activation and fast inactivation is saturated, indicating that the voltage dependence originates from other sources. Slow inactivation of hH1 and [micro]I channels was significantly enhanced by Lqh II and Lqh III. The half-maximal voltage of steady-state slow inactivation was shifted to negative values, the voltage dependence was increased, and, in particular for hH1, slow inactivation at high voltages became more complete. This effect exceeded an expected augmentation of slow inactivation owing to the loss of fast inactivation and, therefore, shows that slow sodium channel inactivation may be directly modulated by scorpion [Alpha]-toxins. KEY WORDS: patch clamp * Leiurus quinquestriatus hebraeus * cardiac muscle * skeletal muscle * receptor site 3

The pore-forming toxin streptolysin O (SLO) can be used to reversibly permeabilize adherent and nonadherent cells, allowing delivery of molecules with up to 100 kDa mass to the cytosol. Using FITC-labeled albumin, [10.sup.5]-[10.sup.6] molecules were estimated to be entrapped per cell. Repair of toxin lesions depended on [Ca.sup.2+]-calmodulin and on intact microtubules, but was not sensitive to actin disruption or to inhibition of protein synthesis. Resealed cells were viable for days and retained the capacity to endocytose and to proliferate. The active domains of large clostridial toxins were introduced into three different cell lines. The domains were derived from Clostridium difficile B-toxin and Clostridium sordelli lethal toxin, which glycosylate small G-proteins, and from Clostridium botulinum C2 toxin, which ADP-ribosylates actin. After delivery with SLO, all three toxins disrupted the actin cytoskeleton to cause rounding up of the cells. Glucosylation assays demonstrated that G-proteins Rho and Ras were retained in the permeabilized cells and were modified by the respective toxins. Inactivation of these G-proteins resulted in reduced stimulus-dependent granule secretion, whereas ADP-ribosylation of actin by the C. botulinum C2-toxin resulted in enhanced secretion in cells. The presented method for introducing proteins into living cells should find multifaceted application in cell biology. protein delivery | pore-forming toxin

Research has been conducted on microaerophilic flagellate parasitic protozoon Giardia intestinalis which can detoxify O (sub)2. The authors have investigated the limits of O (sub)2 tolerance of this microorganism and have characterized the functional and structural consequences of reactive O (sub)2 species accumulation.

We have used a pair of derivatives of [Mu]-conotoxin GIIIA, with titratable residues substituted for the critical arginine-13, to obtain an indication of local pH in the Na channel pore. Wild-type toxin causes all-or-none block of single skeletal muscle Na channels, while residue-13 mutants block only partially. Positive residues in position 13 cause more complete block than neutral or negative ones (Hui and French. 2000. Biophys. J. 78:86A). The docking site of residue-13 has been identified near the channel's selectivity filter (Chang et al. 1998. Biochemistry. 37:4407-4419). Thus, by substituting titratable amino acids for arginine-13 (derivatives R13E and R13H), we generated sensors that should reflect changes in the local pH in the pore as pH varies in the bulk solution. Both binding kinetics and the completeness of single-channel block by these derivatives depended on pH. In general, pH values that favored the neutral form of the residue-13 side chain promoted behavior similar to derivative RI 3A, with neutral alanine in this position. We postulate that the fractional residual current, [F.sub.res] through single channels bound by toxin, and the dissociation rate constant, [k.sub.off], should reflect properties of the toxin-channel bound complex, while the association rate constant, [k.sub.on], should be determined primarily by the state of the free toxin in solution. The fractional current block by R13E and R13H varied with pH with pKs of 6.9 [+ or -] 0.2 and 8.0 [+ or -] 0.4, respectively, whereas for R13A it was independent of pH. The [k.sub.off]s of the titratable mutants had a pK similar to those for the fractional current block. However, their [k.sub.on]s had pKs nearer the nominal values for the side chains of the free amino acids: [is less than] 5 for RI 3E, and [approximately equals] 6.5 for R13H. The results are consistent with a local pH in the vestibule of the toxin-bound channel that is [is greater than or equal to] 1.5 U lower than in bulk solution, suggesting that protons are concentrated in the pore vestibule as befits a cation-selective channel. (Supported by the Medical Research Council of Canada, and the Alberta Heritage Foundation for Medical Research.)

Hanatoxin inhibits voltage-gated [K.sup.+] channels by modifying the energetics of activation. We studied the molecular determinants and physical location of the Hanatoxin receptors on the drk1 voltage-gated [K.sup.+] channel. First, we made multiple substitutions at three previously identified positions in the COOH terminus of S3 to examine whether these residues interact intimately with the toxin. We also examined a region encompassing S1-S3 using alanine-scanning mutagenesis to identify additional determinants of the toxin receptors. Finally, guided by the structure of the KcsA [K.sup.+] channel, we explored whether the toxin interacts with the peripheral extracellular surface of the pore domain in the drk1 [K.sup.+] channel. Our results argue for an intimate interaction between the toxin and the COOH terminus of S3 and suggest that the Hanatoxin receptors are confined within the voltage-sensing domains of the channel, at least 20-25 [Angstrom] away from the central pore axis. KEYWORDS: gating modifier toxin * scanning mutagenesis * voltage-dependent gating * protein-protein interaction

Anthrax causes profound inflammation and systemic shock. A recent study has shown that anthrax lethal toxin represses the transcriptional activity of the glucocorticoid receptor, which is a crucial component of the body's defenses against inflammation. The study reports evidence that lethal toxin blocks the glucocorticoid receptor by inhibiting the p38 mitogen-activated protein kinase pathway. Thus, these findings suggest that glucocorticoid receptor inactivation contributes to anthrax toxicity and raise the possibility of developing new strategies to combat this deadly disease.

Anthrax toxin binds to a plasma membrane receptor and after endocytosis exerts its deadly effects on the cell. Until now, however, the mechanism of initial toxin uptake was unknown. In this issue, Abrami et al. (2003) demonstrate that toxin oligomerization clusters the anthrax receptor into lipid rafts and this complex is internalized via the clathrin-dependent pathway.

Research has been conducted on the cylindrospermopsin and its C7 epimer. The structure of the cylindrospermopsin and its route to its natural C7 epimer have been investigated and the results indicate that the main feature of this route is the intramolecular nitrone cycloaddition.

Research has been conducted on the nitrogen fixation. The synthesis of the pumiliotoxin C isolated from the skin extracts of the Panamanian frog Dendrobates pumilio has been carried out via the keto-alkyne and molecular nitrogen and the results are discussed.

In the cnidarians, the toxins for venom are stored in the tubules of the nematocysts and are translocated via the spirally located series of extended hollow tubular barbs, which looks like a multiheaded poisonous arrow. The toxin is present on the internal surface of the everted-discharged tubule and gets stored near the bases of the low barbs and their lumina.

Abstract. Morphological abnormalities including extra compound eyes, extra heads, and distally duplicated legs were generated in cricket embryos by treating eggs with single doses of either benz[g]isoquinoline-5,10-dione or benzo[h]quinoline-5,6-dione. Slight […]