Rosa E. Navarro

New soluble polyaniline: Synthesis, electrical properties and solution electronic spectrum

Abstract The reaction of aniline with copper(II) perchlorate in acetonitrile yields highly-electroconductive polyaniline perchlorate, [(-C6H4NH-)(ClO4)m·nH2O]x, which is soluble in dimethylsulfoxide (DMSO) and has low degrees of branching and/or crosslinking. The conductivity of a material with m = 0.43 is 3.1 S cm−1 at room temperature. The solution electronic spectrum of the perchlorate exhibits a strong band at 285 nm and a weak band at 445 nm; no band is observed in the region of 830 nm. In the solution electronic spectrum of the corresponding polymer base, strong bands are observed at 630 and 325 nm. When the solution of the polymer base is acidified, the 630 nm band disappears and a new band appears at 830 nm: the protonation of the polymer base by the acidification yields a spectrum that is different from that of the original polymer perchlorate. In the polymer chains of the perchlorate prepared by the present method, the majority of positive charges are centred on anilinium ion radicals (polarons) rather than on quinoneiminium ions (bipolarons).

catA, a new Aspergillus nidulans gene encoding a developmentally regulated catalase

Abstract  Aspergillus nidulans asexual sporulation (conidiation) is a model system for studying gene regulation and development. The CAN5 cDNA is one of several clones isolated based on transcript induction during conidiation. Here we present the molecular characterization of its corresponding gene, demonstrating that it encodes a developmentally regulated catalase, designated catA. The catA 744-amino-acid-residue polypeptide shows significant identity to other catalases. Its similarity to prokaryotic catalases is greater than to other fungal catalases. catA mRNA is barely detectable in growing mycelia, highly induced during sporulation, and present in isolated spores. However, catA expression is not dependent on the developmental regulatory genes brlA, abaA and wetA. Direct catalase activity determination in native gels revealed the existence of two bands of activity. One of these bands represented the major activity during vegetative growth and was induced during sporulation. The second catalase activity appeared after the induction of sporulation and was the predominant activity in spores. Disruption of catA abolished the major spore catalase without eliminating the vegetative activity, indicating the existence of at least two catalase genes in A. nidulans. catA-disrupted mutants produced spores that were sensitive to H2O2, as compared to wild-type spores. The increase in the activity of the vegetative catalase and the appearance of a second catalase during asexual sporulation is consistent with the occurrence of an oxidative stress during development.

Stress-induced germ cell apoptosis by a p53 independent pathway in Caenorhabditis elegans

In Caenorhabditis elegans, several distinct apoptosis pathways have been characterized in the germline. The physiological pathway is though to eliminate excess germ cells during oogenesis to maintain gonad homeostasis and it is activated by unknown mechanisms. The DNA damage-induced germ cell apoptosis occurs in response to genotoxic agents and involves the proteins EGL-1 and CED-13, and the DNA damage response protein p53. Germ cell apoptosis can also be induced in response to pathogen infection through an EGL-1 dependent pathway. To gain insight into the mechanism and functions of germ cell apoptosis, we investigated whether and how other forms of stress induce this cell death. We found that oxidative, osmotic, heat shock and starvation stresses induce germ cell apoptosis through a p53 and EGL-1 independent pathway. We also learned that the MAPK kinases MEK-1 and SEK-1, and the p53 antagonist protein ABL-1, are essential for stress-induced germ cell apoptosis. We conclude that in C. elegans responses to various stresses that do not involve genotoxicity include an increase in germ cell apoptosis through the physiological pathway.

Fungal responses to reactive oxygen species

Reactive oxygen species (ROS) such as hydrogen peroxide, produced externally or during normal metabolism, can damage different cell components and usually trigger a counteracting antioxidant response. The fact that animals and humans utilize ROS and related nitrogen reactive species to prevent fungal infection has generated great interest in defining the components of the antioxidant response and studying their role as virulence determinants in fungi. Here we review the role of specific enzyme and non-enzyme mediated antioxidant mechanisms in virulence, as well as the signal transduction mechanisms that fungal cells use to perceive high ROS levels and induce gene expression. We focus on Schizosaccharomyces pombe antioxidant responses, which involve a prokaryotic-type multistep phosphorelay coupled to a stress-response MAP kinase pathway and an AP-1 type transcription factor, in relation to homologous mechanisms in Aspergillus nidulans and the human pathogen A. fumigatus. Compared to S. pombe and other unicellular fungi, filamentous fungi have additional mechanisms to handle ROS, such as the presence of a larger number of phosphorelay sensor kinases, antioxidant enzymes and secondary metabolites with antioxidant functions. In addition, filamentous fungi have enzymes like the NADPH oxidases, which regulate multicellular development through ROS production and therefore, offer a unique opportunity to study the interplay between ROS production, perception and detoxification, and the role of these processes in cell differentiation and pathogenesis.

CUP-1 is a novel protein involved in dietary cholesterol uptake in Caenorhabditis elegans.

Sterols transport and distribution are essential processes in all multicellular organisms. Survival of the nematode Caenorhabditis elegans depends on dietary absorption of sterols present in the environment. However the general mechanisms associated to sterol uptake in nematodes are poorly understood. In the present work we provide evidence showing that a previously uncharacterized transmembrane protein, designated Cholesterol Uptake Protein-1 (CUP-1), is involved in dietary cholesterol uptake in C. elegans. Animals lacking CUP-1 showed hypersensitivity to cholesterol limitation and were unable to uptake cholesterol. A CUP-1-GFP fusion protein colocalized with cholesterol-rich vesicles, endosomes and lysosomes as well as the plasma membrane. Additionally, by FRET imaging, a direct interaction was found between the cholesterol analog DHE and the transmembrane “cholesterol recognition/interaction amino acid consensus” (CRAC) motif present in C. elegans CUP-1. In-silico analysis identified two mammalian homologues of CUP-1. Most interestingly, CRAC motifs are conserved in mammalian CUP-1 homologous. Our results suggest a role of CUP-1 in cholesterol uptake in C. elegans and open up the possibility for the existence of a new class of proteins involved in sterol absorption in mammals.

Pigment dilution mutants from fish models with connection to lysosome-related organelles and vesicular traffic genes.

An interesting question in developmental biology is why mutations in genes with functions essential for the majority of cells produce diseases affecting only specific tissues. For example, pigment dilution disorders are often the consequence of mutations in conserved vesicular traffic genes. In Hermansky-Pudlak, Griscelli, and Chediak-Higashi pigment dilution syndromes, vesicular traffic mutations affect several organs with one characteristic in common: to carry out their functions they depend to a great extent on lysosome-related organelles (LROs), such as the melanosomes in melanocytes. Conserved multimeric complexes, present in most cell types, target proteins to lysosomes or selected LROs using transport vesicles. By studying these diseases or the model organisms that are defective in these processes, we have learned that every cell type possesses a unique way to regulate its vesicular traffic machinery and to assemble its multimeric complexes. This is accomplished by subunits from these multimeric complexes acting in a cell-specific manner. Here, we review several fish pigment dilution mutants that represent models for human vesicular traffic diseases.

The DEAD Box RNA Helicase VBH-1 Is a New Player in the Stress Response in C. elegans

For several years, DEAD box RNA helicase Vasa (DDX4) has been used as a bona fide germline marker in different organisms. C. elegans VBH-1 is a close homolog of the Vasa protein, which plays an important role in gametogenesis, germ cell survival and embryonic development. Here, we show that VBH-1 protects nematodes from heat shock and oxidative stress. Using the germline-defective mutant glp-4(bn2) we found that a potential somatic expression of vbh-1 might be important for stress survival. We also show that the VBH-1 paralog LAF-1 is important for stress survival, although this protein is not redundant with its counterpart. Furthermore, we observed that the mRNAs of the heat shock proteins hsp-1 and sip-1 are downregulated when vbh-1 or laf-1 are silenced. Previously, we reported that in C. elegans, VBH-1 was primarily expressed in P granules of germ cells and in the cytoplasm of all blastomeres. Here we show that during stress, VBH-1 co-localizes with CGH-1 in large aggregates in the gonad core and oocytes; however, VBH-1 aggregates do not overlap with CGH-1 foci in early embryos under the same conditions. These data demonstrate that, in addition to the previously described role for this protein in the germline, VBH-1 plays an important role during the stress response in C. elegans through the potential direct or indirect regulation of stress response mRNAs.

Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium

O comportamento eletroquimico em funcao da estrutura de uma serie de derivados dos acidos cafeico e ferulico, assim como de seus precursores catecol e guaiacol, eletroquimicamente ativos, foi avaliado por voltametria ciclica. Os resultados revelaram que as condicoes experimentais sao a chave para as mudancas no mecanismo de oxidacao do guaiacol e acido ferulico. A oxidacao eletroquimica dos derivados amida do acido ferulico revelou que o atomo de nitrogenio desempenha um papel importante na derivatizacao da superficie do eletrodo. Alem disso, a atividade sequestradora de radicais dos compostos, avaliada atraves da porcentagem de inibicao do radical 2,2’-difenil-1picril-hidrazila, mostrou uma boa correlacao com os potenciais de oxidacao. We studied the electrochemical behaviour as a function of the structure of a series of caffeic and ferulic acids derivatives as well as their corresponding redox moieties catechol and guaiacol by cyclic voltammetry. Results revealed that the medium is key for changes in the oxidation mechanism of guaiacol and ferulic acid. Electrochemical oxidation of the ferulic acid amide derivatives revealed that the nitrogen atom plays an important role in the derivatization of the electrode surface. In addition, radical scavenging activity of the compounds evaluated through the percentage of inhibition of the 2,2’-diphenyl-1-picrylhidrazyl radical showed a good relationship with the oxidation potentials.

Electronic spectra and structures of Cu2+ and Ni2+ complexes with dioxotetraazacycloalkanediacetates and their diester derivatives

Abstract Functionalized macrocyclic ligands, dioxotetraazacycloalkanediacetic acid, with different ring sizes and their diester derivatives were synthesized, and their Cu 2+ and Ni 2+ chelates were characterized by electronic absorption spectra in solution. A single-crystal X-ray analysis of nickel(II) 2,9-dioxo-1,4,7,10-tetraaza-4,7-cyclotetradecandiacetate pentahydrate showed that the central metal ion had an octahedral coordination with two amine nitrogen atoms, two car☐ylate oxygen atoms and an amide oxygen atom from a ligand molecule and an oxygen atom from a water molecule: the metal complex crystallized in the monoclinic space group P 2 1 / n with a = 9.040(1), b = 13.539(1), c = 18.168(2)A, β = 101.895(2)° and Z = 4. Electronic spectra showed that all the complexes studied had similar structures in acidic solutions. In alkaline solutions, some metal chelates had a distorted planar structure in which two deprotonated amide nitrogen atoms and two amine nitrogen atoms were coordinated to the central metal ion. The tendency of deprotonation of amide groups is dependent on the ring size of the ligand, the nature of the central metal ion and the ability of the pendant arm to coordinate with the central metal ion.

Bioinformatic analysis of P granule-related proteins: insights into germ granule evolution in nematodes.

Germ cells in many animals possess a specialized cytoplasm in the form of granules that contain RNA and protein complexes essential for the function and preservation of the germline. The mechanism for the formation of these granules is still poorly understood; however, the lack of conservation in their components across different species suggests evolutionary convergence in the assembly process. Germ granules are assumed to be present in all nematodes with a preformed germline. However, few studies have clearly identified these structures in species other than Caenorhabditis elegans and even less have carried functional analysis to provide a broader panorama of the granules composition in the phylum. We adopted a bioinformatics approach to investigate the extension of conservation in nematodes of some known C. elegans germ granule components, as a proxy to understand germ granules evolution in this phylum. Unexpectedly, we found that, in nematodes, the DEAD box RNA helicase Vasa, a conserved protein among different phyla, shows a complex history of clade-specific duplications and sequence divergence. Our analyses suggest that, in nematodes, Vasa’s function might be shared among proteins like LAF-1, VBH-1, and GLH-1/-2/-3 and GLH-4. Key components of P granules assembly in C. elegans, like the PGL protein family, are only preserved in Caenorhabditis species. Our analysis suggests that germ granules assembly may not be conserved in nematodes. Studies on these species could bring insight into the basic components required for this pathway.