The physical properties of the capsular polysaccharides from Cryptococcus neoformans suggest features for capsule construction

Diane C. McFadden, Magdia De Jesus, Arturo Casadevall

Research output: Contribution to journalArticle

Abstract

The most distinctive feature of the human pathogenic fungus is a polysaccharide capsule that is essential for virulence and is composed primarily of glucuronoxylomannan (GXM) and galactoxylomannan (GalXM). GXM mediates multiple deleterious effects on host immune function, yet relatively little is known about its physical properties. The average mass of Cryptococcus neoformans GXM from four antigenically different strains ranged from 1.7 to 7 × 106 daltons as calculated from Zimm plots of light-scattering data. GalXM was significantly smaller thanGXM,with an average mass of 1 × 105 daltons. These molecular masses imply that GalXM is the most numerous polysaccharide in the capsule on amolar basis. The radius of gyration of the capsular polysaccharides ranged between 68 and 208 nm. Viscosity measurements suggest that neither polysaccharide altered fluid dynamics during infection since GXM behaved in solution as a polyelectrolyte and GalXM did not increase solution viscosity. Immunoblot analysis indicated heterogeneity within GXM. In agreement with this, scanning transmission electron microscopy of GXM preparations revealed a tangled network of two different types of molecules. Mass per length measurements from light scattering and scanning transmission electron microscopy were consistent and suggested GXM molecules self-associate. Amechanism for capsule growth is proposed based on the extracellular release and entanglement of GXM molecules.

Original languageEnglish (US)
Pages (from-to)1868-1875
Number of pages8
JournalJournal of Biological Chemistry
Volume281
Issue number4
DOIs
StatePublished - Jan 27 2006
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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