Polysaccharides of Fungal Origin: Focus on the Capsule of the Pathogen Cryptococcus neoformans

Cryptococcus neoformans was first isolated as a human pathogen in the 1890s. Subsequent study has shown that the polysaccharide capsule of C. neoformans is a key virulence factor. Unlike in bacteria, the pathways for fungal polysaccharide synthesis are not well characterized with only a single glycosytransferase - Β-(1, 2)-xylosyltranferase Cxt1 - having been confirmed. While there is evidence that polysaccharide synthesis occurs in the cytosol and is transported to the extracellular space in extracellular vesicles, how the capsule attaches to the cell and why some polymers are secreted instead of incorporated into the capsular architecture remains a mystery. In this chapter we explore this along with our current biophysical, structural, and immunological understanding of cryptococcal polysaccharides. From these studies we outline the outstanding questions in the field and identify a bevy of techniques and applications open for future research.