Bothrops moojeni venom kills Leishmania spp. with hydrogen peroxide generated by its L-amino acid oxidase

Leishmaniasis is an endemic tropical disease in South America, with few therapeutic approaches. Snake venoms are complex protein mixtures with biological actions that could be used as tools for drug development. Here we show that Bothrops moojeni crude venom presented a killing effect in vitro against Leishmania spp. promastigotes, but not with amastigotes, as determined by a viability assay using the mitochondrial oxidative function. Purification of active fractions from crude venom was performed by molecular exclusion and ion exchange chromatography. Anti-Leishmania and l-amino acid oxidase (L-AAO, EC.1.4.3.2.) activities co-eluted in the same fractions. The molecular weight of the active enzyme was estimated to be 140 kDa by molecular exclusion chromatography, and 69 kDa by SDS--PAGE, with a 4.8 isoelectric point. Using substrate subtraction and catalase for scavenging, the action of L-AAO was demonstrated to be hydrogen-peroxide-dependent.     

Distinct structural changes detected by X-ray fiber diffraction in stabilization of F-actin by lowering pH and increasing ionic strength

Lowering pH or raising salt concentration stabilizes the F-actin structure by increasing the free energy change associated with its polymerization. To understand the F-actin stabilization mechanism, we studied the effect of pH, salt concentration, and cation species on the F-actin structure. X-ray fiber diffraction patterns recorded from highly ordered F-actin sols at high density enabled us to detect minute changes of diffraction intensities and to precisely determine the helical parameters. F-actin in a solution containing 30 mM NaCl at pH 8 was taken as the control. F-actin at pH 8, 30 to 90 mM NaCl or 30 mM KCl showed a helical symmetry of 2.161 subunits per turn of the 1-start helix (12.968 subunits/6 turns). Lowering pH from 8 to 6 or replacing NaCl by LiCl altered the helical symmetry to 2.159 subunits per turn (12.952/6). The diffraction intensity associated with the 27-A meridional layer-line increased as the pH decreased but decreased as the NaCl concentration increased. None of the solvent conditions tested gave rise to significant changes in the pitch of the left-handed 1-start helix (approximately 59.8 A). The present results indicate that the two factors that stabilize F-actin, relatively low pH and high salt concentration, have distinct effects on the F-actin structure. Possible mechanisms will be discussed to understand how F-actin is stabilized under these conditions.     

Evidence of a sex-dependent association between the MSX1 locus and nonsyndromic cleft lip with or without cleft palate in the Chilean population

Prior studies have implicated an involvement of the Msx1 homeobox gene in cleft palate in mice and its homolog in humans (called MSX1 in the HOX7 gene, located on chromosome 4). In this study we present evidence of a sex-dependent association between MSX1 and non-syndromic cleft lip/palate (NSCLP) in the Chilean population. The sample included 73 NSCLP cases, 37 from multiplex families (Mx), 36 from simplex families (Sx), and 87 controls. Polymerase chain reaction amplification of the MSX1 intragenic microsatellite (CA)n-sequence shows significant (p = 0.035) differences in the allele frequencies between NSCLP-Mx males and control males. These differences are mainly due to frequency differences in allele *2 (173 base pairs) among cases (21.9%) and controls (13.2%). When the NSCLP cases are subdivided by sex and positive family history (Mx versus Sx), the Mx males (27.8%) as well as the total NSCLP-Mx cases (25.7%) showed significantly higher frequencies of allele *2, compared to controls (11.4% and 13.2%, respectively). Analysis of the genotype data indicates that the relative risk for NSCLP is greater for persons carrying allele *2 (i.e., odds ratio [OR] larger than 1), reaching significance for all Mx cases (OR = 2.67; 95% confidence interval [CI], 1.10 to 6.52) and even more pronounced for Mx males (OR = 3.33; 95% CI, 1.08 to 10.32). Taken together, these findings support the hypothesis that the genetic variation at the MSX1 locus is a predisposing gene involved in sex-dependent susceptibility to clefting and that it also differentiates simplex from multiplex families.     

A role for the Ppz Ser/Thr protein phosphatases in the regulation of translation elongation factor 1Balpha

In vivo 32P-labeled yeast proteins from wild type and ppz1 ppz2 phosphatase mutants were resolved by bidimensional electrophoresis. A prominent phosphoprotein, which in ppz mutants showed a marked shift to acidic regions, was identified by mixed peptide sequencing as the translation elongation factor 1Balpha (formerly eEF1beta). An equivalent shift was detected in cells overexpressing HAL3, a inhibitory regulatory subunit of Ppz1. Subsequent analysis identified the conserved Ser-86 as the in vivo phosphorylatable residue and showed that its phosphorylation was increased in ppz cells. Pull-down experiments using a glutathione S-transferase (GST)-EF1Balpha fusion version allowed to identify Ppz1 as an in vivo interacting protein. Cells lacking Ppz display a higher tolerance to known translation inhibitors, such as hygromycin and paromomycin, and enhanced readthrough at all three nonsense codons, suggesting that translational fidelity might be affected. Overexpression of a GST-EF1Balpha fusion counteracted the growth defect associated to high levels of Ppz1 and this effect was essentially lost when the phosphorylatable Ser-86 is replaced by Ala. Therefore, the Ppz phosphatases appear to regulate the phosphorylation state of EF1Balpha in yeast, and this may result in modification of the translational accuracy.     

Partially folded states of the cytolytic protein sticholysin II

Sticholysin II (Stn II) is a cytolytic protein produced by the sea anemone Stichodactyla helianthus, its effect being related to pore formation. The conformation of the protein and its temperature-induced transitions, in the 1.5-12.0 pH range and in the 0-0.5 M NaCl concentration interval, have been studied by circular dichroism and fluorescence spectroscopy. At temperature < 35 degrees C, the protein maintains the same, high beta-structure content, folded conformation in the 1.5-11.0 pH range and ionic strength up to 0.5 M. In the 1.5-3.5 pH range and ionic strength > or = 0.1 M, Stn II shows a thermal transition, resulting in a partially folded state characterized by: (i) a native-like content of regular secondary structure, as detected by far-UV CD; (ii) a largely disordered tertiary structure, as detected by near-UV CD, with partially exposed tryptophan residues according to their fluorescence emission; and (iii) ability to bind the hydrophobic probe 2-anilinonaphthalene-6-sulfonic acid. In the pH range 4.0-10.5, thermally-induced protein aggregation occurs. The obtained results demonstrate the existence of partially folded state of Stn II, which may contribute to the pore formation ability of this cytolysin.     

Distinct properties of wild-type and the amyloidogenic human cystatin C variant of hereditary cerebral hemorrhage with amyloidosis, Icelandic type

Variant human cystatin C (L68Q) is an amyloidogenic protein. It deposits in the cerebral vasculature of Icelandic patients with cerebral amyloid angiopathy, leading to stroke. Wild-type and variant cystatin C are cysteine proteinase inhibitors which form concentration dependent inactive dimers; however, variant cystatin C dimerizes at lower concentrations and has an increased susceptibility to a serine protease. We studied the effect of the L68Q amino acid substitution on cystatin C properties, utilizing full length cystatin C purified in mild conditions from media of cells stably transfected with either the wild-type or variant cystatin C genes. The variant cystatin C forms fibrils in vitro detectable by electron microscopy in conditions in which the wild-type protein forms amorphous aggregates. We also show by circular dichroism, steady-state fluorescence and Fourier-transformed infrared spectroscopy that the amino acid substitution modifies cystatin C structure by destabilizing alpha-helical structures and exposing the tryptophan residue to a more polar environment, yielding a more unfolded molecule. These spectral changes demonstrate that variant cystatin C has a three-dimensional structure different from that of the wild-type protein. The structural differences between variant and wild-type cystatin C account for the susceptibility of the variant protein to unfolding, proteolysis and fibrillogenesis.     

Evaluation of the effect of 90Sr beta-radiation on human blood cells by chromosome aberration and single cell gel electrophoresis (comet assay) analysis

Among various environmental genotoxins, ionizing radiation has received special attention because of its mutagenic, carcinogenic and teratogenic potential. In this context and considering the scarcity of literature data, the objective of the present study was to evaluate the effect of 90Sr beta-radiation on human cells. Blood cells from five healthy donors were irradiated in vitro with doses of 0.2-5.0Gy from a 90Sr source (0.2Gy/min) and processed for chromosome aberration analysis and for comet assay. The cytogenetic results showed that the most frequently found aberration types were acentric fragments, double minutes and dicentrics. The alpha and beta coefficients of the linear-quadratic model, that best fitted the data obtained, showed that 90Sr beta-radiation was less efficient in inducing chromosome aberrations than other types of low linear energy transfer (LET) radiation such as 3H beta-particles, 60Co gamma-rays, 137Cs and 192Ir and X-rays. Apparently, 90Sr beta-radiation in the dose range investigated had no effect on the modal chromosome number of irradiated cells or on cell cycle kinetics. Concerning the comet assay, there was an increase in DNA migration as a function of radiation dose as evaluated by an image analysis system (tail moment) or by visual classification (DNA damage). The dose-response relation adequately fitted the non-linear regression model. In contrast to the cytogenetic data, 90Sr beta-radiation induced more DNA damage than 60Co gamma-radiation when the material was analyzed immediately after exposures. A possible influence of selective death of cells damaged by radiation was suggested.     

Investigation of genotoxic and antigenotoxic activities of chlorophylls and chlorophyllin in cultured V79 cells

Chlorophyll and its derivatives are examples of plant compounds (purified and/or extracted) which appear to protect DNA from damage caused by chemical or physical agents, although some studies have identified clastogenic activity of these compounds. This study was carried out to assess the genotoxic activity of chlorophyll-a (Chl-a), -b (Chl-b) and chlorophyllin (Chl) and their antigenotoxic activity against the DNA damage induced by methyl methanesulphonate (MMS) under conditions of simultaneous, pre-, post-treatment, and simultaneous treatment after pre-incubation of the chemical with MMS. The micronucleus (MN) test was used in binucleated cells (induced by cytochalasin-B) of a mammalian cell line (V79). The three concentrations of Chl-a, Chl-b or Chl (0.1375, 0.275, 0.55microM) were not genotoxic and the genotoxic action of MMS (400microM) decreased (74-117%) under all treatment conditions. The results showed that there was no significant difference among the treatment types, the concentration or the nature of chlorophyll used. The data obtained suggest that Chl-a, Chl-b and Chl when associated with the DNA damaging agent, MMS, may protect the DNA by desgenotoxic action and/or by bio-antigenotoxic mechanisms, with the similar efficiency.     

Telomeric associations in cigarette smokers exposed to low levels of X-rays

Telomeric association (TA), i.e. fusion of chromosomes by their telomeres, predisposes a cell to genetic instability. Because of this we investigated the effect of X-rays exposure and cigarette smoking on the frequency of TA in peripheral blood lymphocytes of exposed individuals, in order to determine if TA can be a chromosomal marker in populations exposed to these carcinogens and if there is an synergistic effect between both agents. We found that the exposed groups show a greater percentage of TA when compared with the control group (P<0.001). However, although the percentage of metaphases with TA in the group with combined exposure (12.6%) was greater than in the others exposed groups (P<0.05), this value was less than the sum of the two individual effects (15.1%). Our results suggest that probably there is not an additive or synergistic effect between X-rays and smoking, and that TA may be a useful cytogenetic marker for evaluating populations exposed to mutagens.