Identification of sialic acids on the cell surface of hyphae and yeast forms of the human pathogen Paracoccidioides brasiliensis

Abstract

Paracoccidiodes 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‐acetlyneuraminic 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 × 106 residues per cell) may inhibit fungal phagocytosis during early infection, when the immunological response is still being built up.

Anionogenic groups and surface sialoglycoconjugate structures of yeast forms of the human pathogen Paracoccidioides brasiliensis

“…Noteworthy was the marked enrichment, as in erythrocytes (Eylar et al, 1962), of terminal 8-galactosyl residues in aged yeast cells of P. brasiliensis, which could favour their phagocytosis. The present evidence for the expression of sialic acids in P. brasiliensis based on their recognition by specific ligands confirms the chemical characterization reported previously (Soares et al, 1993). …”

“…We have previouly shown that both yeast and mycelial forms of P. brasiliensis also expressed surface sialic acid units (Soares et al, 1993). In the present work we extend these studies to establish a correlation between sialic acids and the exposed cell surface anionogenic groups, determining the nature of the sialylated structures expressed in the yeast phase of P. brasiliensis grown in a chemically defined medium.…”

“…S O A R E S a n d OTHERS the binding of fluorescent LFA to whole cells treated with neuraminidase, involved removal of terminal nonreducing units of N-acetylneuraminic acid from yeast surface sialoglycoconjugates. Accordingly, N-acetylneuraminic acid was the only type of sialic acid characterized chemically and spectroscopically in yeast forms of P. brasiliensis (Soares et al, 1993). In addition to strain 339 used in this previous work we also found sialic acids in two other strains of P. brasiliensis (265 and 18) with distinct virulence (unpublished results).…”

“…The carboxyl groups of sialic acids present in glycoproteins and glycolipids also seem to contribute strongly to the negative surface charge (James, 1979;Schauer, 1982). In the current study, treatment of yeast forms of P. brasiliensis with neuraminidase resulted in a significant decrease in the negative surface charge, showing that the carboxyl groups of sialic acids, which amount to 3.6 x lo6 residues per cell (Soares et al, 1993), effectively contribute to the electronegative surface charge. The enzymic removal of sialic acid residues was more effective with neuraminidase from Vibrio cholerae (54.2 O/O reduction) than with that from Clostridium perfringens (30.5 % reduction), suggesting the occurrence of different sialylated structures.…”

“…Sialic acids are linked to P-D-galactose in sialylglycoconjugates, as also confirmed in P. brasiliensis, which became more strongly agglutinated by PNA after neuraminidase treatment (Soares et al, 1993). The sialic acid-galactose bonds involve a2,6 and a2,3 linkages as determined in the current study, using, respectively, influenza A M1/5 and M1/5 HS8 virus strains as probes.…”