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Chapter 6 : The Cell Wall of Cryptococcus
Category: Clinical Microbiology; Fungi and Fungal Pathogenesis
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The fungal cell wall is an essential organelle, vital for maintaining cell integrity against various chemical, physical, and biological stressors. This chapter covers work on the cell wall of Cryptococcus, drawing on studies from fungi such as Saccharomyces cerevisiae, Candida albicans, Schizosaccharomyces pombe, Histoplasma capsulatum, and Aspergillus fumigatus, for introduction and comparison. Certain cell wall components can be up- or downregulated in response to various external conditions. The fungal cell wall contains several different components, and much is understood regarding their structures and mechanisms of synthesis. Certain proteins, such as Gas1p and Bgl2p, have been proposed to function in cell wall organization, but definitive studies are still needed. Future investigations in this area promise to dramatically increase our understanding of cell wall assembly and dynamics. Our understanding of the evolution of fungal cell wall proteins will advance with fungal genome sequencing. Studies of Cryptococcus neoformans have revealed that its cell wall is very different from and more complex than other well-characterized fungal cell walls. Mutants of Cryptococcus lacking β-1, 6-glucan, and therefore having decreased retention of cell wall proteins, appear to have shifts in chitosan localization. The fungal cell wall remains the most attractive target for the next generation of antifungal drugs.
Quick-freeze deep-etch scanning electron micrograph of the cell wall of Cryptococcus illustrating the attachment of capsule and the two layers of the cell wall. Micrograph kindly provided by Tamara Doering and John Heuser.
Major cell wall polysaccharides of select fungal organisms
Extracellular proteins of Cryptococcus neoformans