Loss of cell wall alpha(1‐3) glucan affects Cryptococcus neoformans from ultrastructure to virulence

Abstract

SummaryYeast cell walls are critical for maintaining cell integrity, particularly in the face of challenges such as growth in mammalian hosts. The pathogenic fungus Cryptococcus neoformans additionally anchors its polysaccharide capsule to the cell surface via a(1-3) glucan in the wall. Cryptococcal cells disrupted in their alpha glucan synthase gene were sensitive to stresses, including temperature, and showed difficulty dividing. These cells lacked surface capsule, although they continued to shed capsule material into the environment. Electron microscopy showed that the alpha glucan that is usually localized to the outer portion of the cell wall was absent, the outer region of the wall was highly disorganized, and the inner region was hypertrophic. Analysis of cell wall composition demonstrated complete loss of alpha glucan accompanied by a compensatory increase in chitin/chitosan and a redistribution of beta glucan between cell wall fractions. The mutants were unable to grow in a mouse model of infection, but caused death in nematodes. These studies integrate morphological and biochemical investigations of the role of alpha glucan in the cryptococcal cell wall.

Role for Chitin and Chitooligomers in the Capsular Architecture of Cryptococcus neoformans

“…␣-1,3-Glucan was the first cell wall component associated to capsule anchoring. Cryptococcal cells with disrupted ␣-glucan synthase genes had normal biosynthesis of capsular material but lacked a surface capsule (30). Mutant cells lacking ␣-1,3-glucan also had modified cell walls (30), strengthening the notion that the lack of cell wall glucans could impair buildup of the cell wall and cell wall-capsule connections.…”

“…Anchoring of the capsule or capsule precursors to the cell wall is crucial for the pathogenicity of C. neoformans since capsular components are required for virulence. The interactions between the components of the cell wall and the capsule responsible for attaching the capsule to the cell wall remain poorly understood, but various reports suggest that the surface connections are complex and could involve multiple cell wall components (29,30,32). ␣-1,3-Glucan was the first cell wall component associated to capsule anchoring.…”

“…Seemingly, the assembly of the surface envelope of C. neoformans requires the interaction of cell wall components with capsular elements. Some of the cryptococcal cell wall-capsule connectors have been identified, including the structural polysaccharide ␣-1,3-glucan and chitooligomers (29,30,32).…”

Discovery and Characterization of a Peptoid with Antifungal Activity against Cryptococcus neoformans

“…31 The MIC of AEC5 against all these organisms ranged from 6.3 to 25 μg/mL, while the IC 50 ranged from 0.68 to 12.2 μg/mL (Table 1 and Figure S3). Given that serotypes A and D are 15% different genetically 32 and the composition of the cell walls are likely different, 33,34 it is not surprising that this compound is not as potent against clinical isolates of serotype D.…”

Usefulness of silkworm as a host animal for understanding pathogenicity of <i>Cryptococcus neoformans </i>

“…Capsule and other virulence factors of C. neoformans, which are needed to exhibit the pathogenicity against mammals, were reported to be needed to exhibit the pathogenicity against C. elegans (7). C. elegans was also used to screen virulence factors of C. neoformans (29)(30)(31)(32)(33)(34)(35)(36). Moreover, C. neoformans infection model with C. elegans was also used to evaluate therapeutic effects of antifungal reagents (37,38).…”