Navegando por Palavras-chave "SIALIC ACID"

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    IDENTIFICATION OF SIALIC ACIDS ON THE CELL-SURFACE OF HYPHAE AND YEAST FORMS OF THE HUMAN PATHOGEN PARACOCCIDIOIDES-BRASILIENSIS
    (Elsevier B.V., 1993-03-15) Soares, RMA; Alviano, C. S.; Angluster, J.; Travassos, Luiz Rodolpho [UNIFESP]; Universidade Federal do Rio de Janeiro (UFRJ); Universidade Federal de São Paulo (UNIFESP)
    Paracoccidioides brasiliensis, the agent of paracoccidioidomycosis, when grown in a synthetic medium, expresses at the cell surface of both yeast and mycelial forms acidic glycoconjugates containing N-acetylneuraminic acid units. Sialic acids were extracted using mild hydrolytic conditions, and were identified by thin-layer and gas chromatography, standard colorimetry, reaction with periodate-resorcinol and mass spectrometry. Their surface location was inferred from fluorescent-lectin (Limulus polyphemus agglutinin) binding to whole cells abrogated by previous treatment with neuraminidase. Expression of sialic acids on virulent yeast forms of P. brasiliensis (3.7 X 10(6) residues per cell) may inhibit fungal phagocytosis during early infection, when the immunological response is still being built up.
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    MUCIN-LIKE GLYCOPROTEINS LINKED TO the MEMBRANE BY GLYCOSYLPHOSPHATIDYLINOSITOL ANCHOR ARE the MAJOR ACCEPTORS of SIALIC-ACID in A REACTION CATALYZED BY TRANS-SIALIDASE in METACYCLIC FORMS of TRYPANOSOMA-CRUZI
    (Elsevier B.V., 1993-06-01) Schenkman, S.; Ferguson, MAJ; Heise, N.; Dealmeida, MLC; Mortara, R. A.; Yoshida, N.; UNIV DUNDEE; Universidade Federal de São Paulo (UNIFESP)
    We have previously shown that 35- and 50-kDa glycoconjugates of cultured metacyclic trypomastigotes participate in the attachment of parasites to mammalian cells. Here we show that when metacyclic trypomastigotes are incubated with [H-3]sialyllactose, most of the sialic acid is transferred to these 35/50-kDa molecules in a reaction catalyzed by a parasite transsialidase. the sialic acid is incorporated in oligosaccharides of about 10 glucose units in size that are released from the glycoconjugate by mild alkaline hydrolysis. Compositional analysis reveals that the 35/50-kDa molecules are highly glycosylated proteins rich in threonine, galactose, N-acetyl-glucosamine and sialic acid. These glycoproteins can be labeled in vivo with [H-3]palmitate, and the labeled fatty acid is released by glycosylphosphatidylinositol specific phospholipases C. This result, associated with the fact that they contain mannose, ethanolamine, myo-inositol, and lipid, indicate that these glycoproteins are anchored to the membrane by glycosylphosphatidylinositol. During cell invasion, these molecules appear to be capped and locally released by the parasite.
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    SUBSTRATE-SPECIFICITY of the TRYPANOSOMA-CRUZI TRANS-SIALIDASE
    (Oxford Univ Press United Kingdom, 1992-12-01) Vandekerckhove, F.; Schenkman, Sergio [UNIFESP]; Decarvalho, L. P.; Tomlinson, S.; Kiso, M.; Yoshida, M.; Hasegawa, A.; NUSSENZWEIG, V; Universidade Federal de São Paulo (UNIFESP); GIFU UNIV
    Trypanosoma cruzi trypomastigotes acquire sialic acid (SA) from host glycoconjugates by means of a plasma membrane-associated trans-sialidase (TS). Here we study the substrate specificity of TS, which differs from all known sialyl-transferases in that it does not require cytidine monophosphate (CMP)-SA as donor. the T.cruzi TS reversibly transfers SA to saccharides with terminal beta-Gal (but not alpha-Gal) residues. Donors are saccharides with SA linked to terminal beta-Gal residues by (alpha2-3), but not (alpha2-6) bonds. the type of beta-linkage of the terminal Gal residue is of minor importance (beta1-4 and beta1-6 are slightly better than beta1-3), whereas chain length and the structure of additional vicinal sugar residues are not relevant. SA on the surface of living trypomastigotes of T.cruzi is transferred back and forth between the parasite surface and acceptor molecules with terminal beta-Gal, either in solution or on the surface of neighbouring mammalian cells. Addition of fucose residue on or close to the terminal galactose impairs TS activity. As a consequence, the enzyme acts poorly on the E-selectin ligand sialyl-Lewis(x) and its precursor Lewis(x), and in vitro adhesion of TS-treated neutrophils to L-cells expressing L-selectin is not affected. Modifications in the structure of the (alpha2-3)-linked N-acetyl-neuraminic acid (Neu5Ac) (deoxy or methoxy) of the donor molecules do not impair transfer if the changes are at C-9, whereas changes at C4, C-7 and C-8 impair the ability to donate the modified SA. Compounds with modified C4 and C-8 inhibit TS at relatively high inhibitor/substrate ratios.
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    TRANS-SIALIDASE FROM TRYPANOSOMA-CRUZI EPIMASTIGOTES IS EXPRESSED AT the STATIONARY-PHASE and IS DIFFERENT FROM the ENZYME EXPRESSED in TRYPOMASTIGOTES
    (Elsevier B.V., 1993-09-01) Chaves, L. B.; Briones, MRS; Schenkman, S.; Universidade Federal de São Paulo (UNIFESP)
    We have studied the trans-sialidase from insect forms of Trypanosoma cruzi growing in axenic culture. Log phase epimastigotes expressed little or-no trans-sialidase activity, and were unable to incorporate exogenous sialic acid. Trans-sialidase started to be expressed at the late logarithmic phase, with specific activity increasing steadily as the culture reached the stationary phase. Trans-sialidase was purified from the late log phase epimastigote culture, which contained less than 2% of metacyclic forms, yielding a glycoprotein that migrated as a single 90-kDa band in sodium dodecyl sulfate gels. This enzyme features: (1) no reaction with antibodies against the peptide repeats present in the carboxy-terminal of trypomastigote trans-sialidase; (2) positive reaction with antibodies raised against a fragment of trypomastigote trans-sialidase that contains the active site; (3) similar kinetic properties and identical acceptor-donor specificity when compared to the trypomastigote enzyme; and (4) neuraminidase activity in the absence of acceptors. Upon differentiation into metacyclic forms, a trans-sialidase activity containing the carboxy-terminal repeats of the trypomastigote enzyme was released into the medium. These results suggest that epimastigotes express a developmentally regulated trans-sialidase that contains the same catalytic site but lacks the tandem amino acid repeats typical of trypomastigote trans-sialidase.