Capsular localization of the Cryptococcus neoformans polysaccharide component galactoxylomannan

Magdia De Jesus, André Moraes Nicola, Marcio L. Rodrigues, Guilhem Janbon, Arturo Casadevall

Research output: Contribution to journalArticle

Abstract

Cryptococcus neoformans capsular polysaccharide is composed of at least two components, glucuronoxylomannan (GXM) and galactoxylomannans (GalXM). Although GXM has been extensively studied, little is known about the location of GalXM in the C. neoformans capsule, in part because there are no serological reagents specific to this antigen. To circumvent the poor immunogenicity of GalXM, this antigen was conjugated to protective antigen from Bacillus anthracis as a protein carrier. The resulting conjugate elicited antibodies that reacted with GalXM in mice and yielded an immune serum that proved useful for studying GalXM in the polysaccharide capsule. In acapsular cells, immune serum localized GalXM to the cell wall. In capsulated cells, immune serum localized GalXM to discrete pockets near the capsule edge. GalXM was abundant on the nascent capsules of budding daughter cells. The constituent sugars of GalXM were found in vesicle fractions consistent with vesicular transport for this polysaccharide. In addition, we generated a single-chain fraction variable fragment antibody with specificity to oxidized carbohydrates that also produced punctate immunofluorescence on encapsulated cells that partially colocalized with GalXM. The results are interpreted to mean that GalXM is a transient component of the polysaccharide capsule of mature cells during the process of secretion. Hence, the function of GalXM appears to be more consistent with that of an exopolysaccharide than a structural component of the cryptococcal capsule.

Original languageEnglish (US)
Pages (from-to)96-103
Number of pages8
JournalEukaryotic Cell
Volume8
Issue number1
DOIs
StatePublished - Jan 2009
Externally publishedYes

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ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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