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Eukaryotic Cell, March 2006, p. 488-498, Vol. 5, No. 3
1535-9778/06/$08.00+0     doi:10.1128/EC.5.3.488-498.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Lipid Rafts in Cryptococcus neoformans Concentrate the Virulence Determinants Phospholipase B1 and Cu/Zn Superoxide Dismutase

A. Rosemary Siafakas, Lesley C. Wright, Tania C. Sorrell, and Julianne T. Djordjevic*

Centre for Infectious Diseases & Microbiology and Westmead Millennium Institute, University of Sydney at Westmead, Level 3, ICPMR Building, Institute Road, Westmead, NSW 2145, Australia

Received 16 June 2005/ Accepted 29 November 2005

Lipid rafts have been identified in the membranes of mammalian cells, the yeast Saccharomyces cerevisiae, and the pathogenic fungus Candida albicans. Formed by a lateral association of sphingolipids and sterols, rafts concentrate proteins carrying a glycosylphosphatidylinositol (GPI) anchor. We report the isolation of membranes with the characteristics of rafts from the fungal pathogen Cryptococcus neoformans. These characteristics include insolubility in Triton X-100 (TX100) at 4°C, more-buoyant density within a sucrose gradient than the remaining membranes, and threefold enrichment with sterols. The virulence determinant phospholipase B1 (PLB1), a GPI-anchored protein, was highly concentrated in raft membranes and could be displaced from them by treatment with the sterol-sequestering agent methyl-ß-cyclodextrin (MßCD). Phospholipase B enzyme activity was inhibited in the raft environment and increased 15-fold following disruption of rafts with TX100 at 37°C. Treatment of viable cryptococcal cells in suspension with MßCD also released PLB1 protein and enzyme activity, consistent with localization of PLB1 in plasma membrane rafts prior to secretion. The antioxidant virulence factor Cu/Zn superoxide dismutase (SOD1) was concentrated six- to ninefold in raft membrane fractions compared with nonraft membranes, whereas the cell wall-associated virulence factor laccase was not detected in membranes. We hypothesize that raft membranes function to cluster certain virulence factors at the cell surface to allow efficient access to enzyme substrate and/or to provide rapid release to the external environment.

* Corresponding author. Mailing address: Centre for Infectious Diseases & Microbiology, Level 3, ICPMR Building, Westmead Hospital, Westmead, NSW 2145, Australia. Phone: (61) 29845 7046. Fax: (61) 29891 5317. E-mail: julianned{at}icpmr.wsahs.nsw.gov.au.

Eukaryotic Cell, March 2006, p. 488-498, Vol. 5, No. 3
1535-9778/06/$08.00+0     doi:10.1128/EC.5.3.488-498.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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