Roland Schauer

Publications (3)6.57 Total impact

• Article: Characterization of sialidase from an influenza A (H3N2) virus strain: kinetic parameters and substrate specificity.

  José França de Barros, Daniela Sales Alviano, Maria Helena da Silva, Marcia Dutra Wigg, Celuta Sales Alviano, Roland Schauer, José Nelson dos Santos Silva Couceiro
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  ABSTRACT: Neuraminidase (NA) of influenza A (H3N2) viruses was characterized after purification by gel filtration and proteolytic treatment, using the X-31 variant strain that is a reassortment between the influenza A/Victoria/3/75 (responsible for the 1975 pandemic) and the influenza A/PR/8/34 virus samples, as a model. In the purification process, NA heads, that is the spike responsible for the virus sialidase activity, were purified by filtration through a Bio-Gel polyacrylamide column. The enzyme activity was determined by periodic acid/thiobarbituric acid assay and high-performance thin-layer chromatography. The sialidase showed preference for the alpha-2,3-linkage over the alpha-2,6-linkage of sialyllactoses (K(m) of 1.8 and 5.2 x 10(-4)M, respectively) at pH 5.2. The enzyme acted on natural and synthetic substrates at different hydrolysis rates, as well as on human erythrocytes (A group, Rh+) and yeast (CANDIDA ALBICANS) cells. The active NA produced by gel filtration was characterized by different parameters of its sialidase activity, also showing to be a suitable tool for the identification of natural sialocompounds and for the screening of antisialidase drugs to treat influenza virus infections.
  Intervirology 02/2003; 46(4):199-206. · 2.34 Impact Factor
• Article: Sialylglycoconjugates and sialyltransferase activity in the fungus Cryptococcus neoformans.

  Marcio L Rodrigues, Andrey S S Dobroff, José Nelson dos S S Couceiro, Celuta S Alviano, Roland Schauer, Luiz R Travassos
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  ABSTRACT: Cryptococcus neoformans is a fungal pathogen associated with systemic mycoses in up to 10% of AIDS patients. C. neoformans yeasts express sialic acids on the cell wall, where they play an anti-phagocytic role, and may represent a virulence factor at the initial phase of infection. Since the nature of the sialic acid-carrying components is undefined in C. neoformans, our aim in the present work was to identify sialylated molecules in this fungus and study the sialylation process. C. neoformans yeast forms were cultivated in a chemically defined medium free of sialic acids, to search for autologous sialylglycoconjugates. Sialylated glycolipids were not detected. Two glycoproteins with molecular masses of 38 and 67 kDa were recognized by Sambucus nigra agglutinin, an alpha2,6-sialic acid-specific lectin. The 67 kDa glycoprotein also interacted with Influenza C virus, but not with Limax flavus agglutinin, suggesting the presence of the 9-O-acetylated sialic acid derivative as a constituent of the oligosaccharide chains. A partially purified protein fraction from cryptococcal yeast forms was able to transfer sialic acid from CMP-Neu5Ac to both N-(acetyl-1-(14)C)-lactosamine and asialofetuin. Additional evidence for a sialyltransferase in C. neoformans was obtained through the reactivity of fungal proteins with rabbit anti-rat alpha2,6 sialyltransferase polyclonal antibody. Our results indicate that sialic acids in C. neoformans are linked to glycoproteins, which are sialylated by the action of a fungal sialyltransferase. This is the first demonstration of this biosynthetic step in pathogenic fungi.
  Glycoconjugate Journal 04/2002; 19(3):165-73. · 2.12 Impact Factor
• Article: Sialic acids in fungi

  Celuta S. Alviano, Luiz R. Travassos, Roland Schauer
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  ABSTRACT: The increasing number of reports on the presence of sialic acids in fungi (N-acetyl, N-glycolyl-and 5,9-N,O-diacetyl neuraminic acids) based on direct and indirect evidence warrants the present review. Formerly suggested as sialidase-sensitive sources of anionic groups at the cell surface of fungal species grown in chemically defined media (e.g., Fonsecaea pedrosoi), sialic acids have also been found in Sporothrix schenckii, Paracoccidioides brasiliensis, Cryptococcus neoformans and recently, in Candida albicans. Methods used involved adequate hydrolysis and extraction procedures, HTPLC, gas-chromatography, colorimetry, mass spectroscopy, sialidase-sensitive lectin and influenza virus binding. Apart from protecting fungal cells against phagocytosis (S. schenckii, C. neoformans) and playing a cellular structural role (F. pedrosoi), other biological functions of sialic acids are still being investigated.
  Glycoconjugate Journal 08/1999; 16(9):545-554. · 2.12 Impact Factor