Regioselective degradation of [beta] 1,3 glucan by ferrous ion and hydrogen peroxide (Fenton oxidation).

Many species use Fe+2 and H2O2 to oxidize a wide variety of compounds to simpler molecules. Both pathogen killing by leukocytes (neutrophils and lymphocytes) and degradation of cellulose by brown rot fungi rely on excretion of Fe+2 ions and H2O2, the Fenton reagent. To elucidate the mechanism of Fenton oxidation of carbohydrates, ß1,3 glucan (laminaran), a major fungal wall polysaccharide, was oxidized using a molar ratio of monomer/Fe+2/H2O2 of 10:1:1 (primarily). We labeled the reaction products and profiled them as fluorescent-labeled molecules in polyacrylamide gels and as hydrophobic-tagged molecules using reverse phase liquid chromatography/mass spectrometry (HPLC/MS). Sub-stoichiometric concentrations of Fe+2 and H2O2 fragmented laminaran into smaller molecules containing carbonyl and carboxylic acid groups visible on fluorescent-labeled carbohydrate polyacrylamide gel electrophoresis. HPLC/MS analysis of glucan fragments showed masses consistent with six classes of molecules: aldoses, dialdoses, uronic acids, hexosuloses, aldonic acids, and hexulosonic acids. The results were consistent with published mechanisms where hydrogen radical (H•) abstraction from a C-H or O-H bond begins a cascade of reactions leading to 1) C-C bond cleavage to produce aldose/dialdose pairs; 2) oxo-group (O = ) addition to produce uronic and aldonic acids; 3) hydroxyl group (HO-) addition to produce gluconolactone and hexosuloses; and 4) hexulosonic acids. Most products resulted from regioselective H• abstractions characteristic of oxidations by ferryl-oxo ion [(FeO)+2] or perferryl-oxo ion [(FeO)+3] in close contact with specific positions in the glycan. Therefore, oxidations initiated by regioselectively-bound Fe ions were the predominant initiators of polysaccharide degradations.

Group 11 Metal Compounds with Tripodal Bis(imidazole) Thioether Ligands. Applications as Catalysts in the Oxidation of Alkenes and as Antimicrobial Agents.

New group 11 metal complexes have been prepared using the previously described tripodal bis(imidazole) thioether ligand (N-methyl-4,5-diphenyl-2-imidazolyl)2C(OMe)C(CH3)2S(tert-Bu) ({BITOMe,StBu}, 2). The pincer ligand offers a N2S donor atom set that can be used to coordinate the group 11 metals in different oxidation states [AuI, AuIII, AgI, CuI and CuII]. Thus the new compounds [Au{BITOMe,StBu}Cl][AuCl4]2 (3), [Au{BITOMe,StBu}Cl] (4), [Ag{BITOMe,StBu}X] (X = OSO2CF3- 5, PF6- 6) and [Cu{BITOMe,StBu}Cl2] (7) have been synthesized from reaction of 2 with the appropriate metal precursors, and characterized in solution. While attempting characterization in the solid state of 3, single crystals of the neutral dinuclear mixed AuIII-AuI species [Au2{BITOMe,S}Cl3] (8) were obtained and its crystal structure was determined by X-ray diffraction studies. The structure shows a AuIII center coordinated to the pincer ligand through one N and the S atom. The soft AuI center coordinates to the ligand through the same S atom that has lost the tert-butyl group, thus becoming a thiolate ligand. The short distance between the AuI-AuIII atoms (3.383 Å) may indicate a weak metal-metal interaction. Complexes 2-7 and the previously described CuI compound [Cu{BITOMe,StBu}]PF6 (9) have been evaluated in the oxidation of biphenyl ethylene with tert-butyl hydrogen peroxide (TBHP) as the oxidant. Results have shown that the AuI and AgI complexes 4 and 6 (at 10 mol % loading) are the more active catalysts in this oxidative cleavage. The antimicrobial activity of compounds 2-5, 7 and 9 against Gram-positive and Gram-negative bacteria and yeast has also been evaluated. The new gold and silver compounds display moderate to high antibacterial activity, while the copper derivatives are mostly inactive. The gold and silver complexes were also potent against fungi. Their cytotoxic properties have been analyzed in vitro utilizing HeLa human cervical carcinoma cells. The compounds displayed a very low cytotoxicity on this cell line (5 to 10 times lower than cisplatin) and on normal primary cells derived from C57B6 mouse muscle explants, which may make them promising candidates as potential antimicrobial agents and safer catalysts due to low toxicity in human and other mammalian tissues.

A screen for deficiencies in GPI-anchorage of wall glycoproteins in yeast.

Many of the genes and enzymes critical for assembly and biogenesis of yeast cell walls remain unidentified or poorly characterized. Therefore, we designed a high throughput genomic screen for defects in anchoring of GPI-cell wall proteins (GPI-CWPs), based on quantification of a secreted GFP-Sag1p fusion protein. Saccharomyces cerevisiae diploid deletion strains were transformed with a plasmid expressing the fusion protein under a GPD promoter, then GFP fluorescence was determined in culture supernatants after mid-exponential growth. Variability in the amount of fluorescent marker secreted into the medium was reduced by growth at 18 degrees C in buffered defined medium in the presence of sorbitol. Secondary screens included immunoblotting for GFP, fluorescence emission spectra, cell surface fluorescence, and cell integrity. Of 167 mutants deleted for genes affecting cell wall biogenesis or structure, eight showed consistent hyper-secretion of GFP relative to parental strain BY4743: tdh3 (glyceraldehyde-3-phosphate dehydrogenase), gda1 (guanosine diphosphatase), gpi13 and mcd4 (both ethanolamine phosphate-GPI-transferases), kre5 and kre1 (involved in synthesis of beta1,6 glucan), dcw1(implicated in GPI-CWP cross-linking to cell wall glucan), and cwp1 (a major cell wall protein). In addition, deletion of a number of genes caused decreased secretion of GFP. These results elucidate specific roles for specific genes in cell wall biogenesis, including differentiating among paralogous genes.

Water Soluble Phosphane-Gold(I) Complexes. Applications as Recyclable Catalysts in a Three-component Coupling Reaction and as Antimicrobial and Anticancer Agents.

Water-soluble compounds of the type [AuCl(PR3)] with alkyl-bis-(m-sulfonated-phenyl)-(mC6H4SO3Na)2 and dialkyl-(m-sulfonated-phenyl)-(mC6H4SO3Na) (R = nBu, Cp) phosphanes have been prepared. Dialkyl-phosphane compounds generate water-soluble nanoparticles of 10-15 nm radius when dissolved in water. These air-stable complexes have been evaluated as catalysts in the synthesis of propargylamines via a three-component coupling reaction of aldehydes, amines and alkynes in water. The antimicrobial activity of the new complexes against Gram-positive and Gram-negative bacteria and yeast has been evaluated. The new compounds display moderate to high antibacterial activity. The more lipophilic compounds are also potent against fungi. Their cytotoxic properties have been analyzed in vitro utilizing human Jurkat T-cell acute lymphoblastic leukemia cells. Compounds with dialkyl-(m-sulfonated-phenyl)-(mC6H4SO3Na) phosphanes displayed moderate to high cytotoxicity on this cell line. Death cell mechanism occurs mainly by early apoptosis. The catalytic/biological activity of the previously described compound with commercial m-trisulfonated-triphenylphosphine [AuCl(TPPTS)] (6) has been also evaluated to compare the effects of the higher basicity and lipophilicity of the alkyl- and di-alkyl-(m-sulfonated-phenyl) phosphanes on these new compounds.

Evidence for the role of calcineurin in morphogenesis and calcium homeostasis during mycelium-to-yeast dimorphism of Paracoccidioides brasiliensis.

Paracoccidioides brasiliensis is a dimorphic fungus that causes paracoccidioidomycosis, the most prevalent human deep mycosis in Latin America. The dimorphic transition from mycelium to yeast (M-Y) is triggered by a temperature shift from 25 degrees C to 37 degrees C and is critical for pathogenicity. Intracellular Ca(2+) levels increased in hyphae immediately after temperature-induced dimorphism. The chelation of Ca(2+) with extracellular (EGTA) or intracellular (BAPTA) calcium chelators inhibited temperature-induced dimorphism, whereas the addition of extracellular Ca(2+) accelerated dimorphism. The calcineurin inhibitor cyclosporine A (CsA), but not tacrolimus (FK506), effectively decreased cell growth, halted the M-Y transition that is associated with virulence, and caused aberrant growth morphologies for all forms of P. brasiliensis. The difference between CsA and FK506 was ascribed by the higher levels of cyclophilins contrasted to FKBPs, the intracellular drug targets required for calcineurin suppression. Chronic exposure to CsA abolished intracellular Ca(2+) homeostasis and decreased mRNA transcription of the CCH1 gene for the plasma membrane Ca(2+) channel in yeast-form cells. CsA had no detectable effect on multidrug resistance efflux pumps, while the effect of FK506 on rhodamine excretion was not correlated with the transition to yeast form. In this study, we present evidence that Ca(2+)/calmodulin-dependent phosphatase calcineurin controls hyphal and yeast morphology, M-Y dimorphism, growth, and Ca(2+) homeostasis in P. brasiliensis and that CsA is an effective chemical block for thermodimorphism in this organism. The effects of calcineurin inhibitors on P. brasiliensis reinforce the therapeutic potential of these drugs in a combinatory approach with antifungal drugs to treat endemic paracoccidioidomycosis.

Implications for the existence of a heptasulfur linkage in natural o-benzopolysulfanes.

Natural o-benzopolysulfanes are often thought to exist as either the trisulfane or pentasulfane; the nomenclature has evolved around such notions. No study makes reference to the possible existence of natural o-benzoheptasulfanes. The work performed here indicates that a facile equilibration takes place between the tri-, penta-, and heptasulfanes (o-C(6)H(4)S(3), o-C(6)H(4)S(5), and o-C(6)H(4)S(7)) in solution. In these simpler (unnatural) compounds, the number of sulfur atoms can be established unequivocally from their independent syntheses. The o-benzopolysulfanes, even after purification, yield mixtures of compounds in solution. A similar equilibration may be anticipated for the corresponding natural products.

The ER-Golgi v-SNARE Bet1p is required for cross-linking alpha-agglutinin to the cell wall in yeast.

In Saccharomyces cerevisiae, glycosylphosphatidylinositol (GPI)-anchored cell wall mannoproteins, including alpha-agglutinin, are secreted to the cell surface through vesicular transport pathways. At the cell surface the GPI anchors are cleaved within the glycan, then transglycosylated to form a covalent cross-link to 1,6-beta-glucan. Among mutants that were temperature-sensitive for growth and for ability to cross-link the mannoprotein alpha-agglutinin to the cell wall, one strain was complemented by BET1, which encodes an ER-Golgi v-SNARE. Temperature-sensitive mutations in BET1 caused aberrations in cell wall structure, including excretion of alpha-agglutinin into the medium, sensitivity to lysis with Zymolyase and hypersensitivity to Calcofluor White. At restrictive temperatures, bet1 mutations block secretion of invertase and other proteins, but alpha-agglutinin was excreted into the extracellular medium. In wild-type parental or bet1 cells, secretion of alpha-agglutinin also continued after protein synthesis was blocked with cycloheximide. This secretion was due to continued export of a significant amount of alpha-agglutinin from compartments distal to the BET1-dependent secretion step. Thus, in bet1 cells the ER-Golgi block allowed secretion to continue, but prevented cell wall incorporation of the alpha-agglutinin. Therefore, a mutation early in the secretion pathway caused aberrant cell wall synthesis by preventing localization of key components required in wall cross-links.