Extracellular Vesicles Produced by <i>Cryptococcus neoformans</i> Contain Protein Components Associated with Virulence

TLDR

Cryptococcus neoformans secretes extracellular vesicles that carry its major virulence factor glucuronoxylomannan across the cell wall into the extracellular space, where it may support capsule growth or be delivered to host tissues. The study aims to characterize the morphology and protein composition of these vesicles. This was done using electron microscopy, proteomic analysis, enzymatic activity assays, and serological reactivity. Proteomic analysis identified 76 proteins, including virulence factors and oxidative‑stress‑protective proteins, while biochemical tests detected laccase and urease activities; electron microscopy revealed vesicles of diverse sizes and morphologies, and patient sera recognized distinct vesicle proteins, supporting the view that extracellular vesicles function as virulence bags delivering concentrated fungal products to host cells.

Abstract

ABSTRACT Cryptococcus neoformans produces vesicles containing its major virulence factor, the capsular polysaccharide glucuronoxylomannan (GXM). These vesicles cross the cell wall to reach the extracellular space, where the polysaccharide is supposedly used for capsule growth or delivered into host tissues. In the present study, we characterized vesicle morphology and protein composition by a combination of techniques including electron microscopy, proteomics, enzymatic activity, and serological reactivity. Secretory vesicles in C. neoformans appear to be correlated with exosome-like compartments derived from multivesicular bodies. Extracellular vesicles manifested various sizes and morphologies, including electron-lucid membrane bodies and electron-dense vesicles. Seventy-six proteins were identified by proteomic analysis, including several related to virulence and protection against oxidative stress. Biochemical tests indicated laccase and urease activities in vesicles. In addition, different vesicle proteins were recognized by sera from patients with cryptococcosis. These results reveal an efficient and general mechanism of secretion of pathogenesis-related molecules in C. neoformans , suggesting that extracellular vesicles function as “virulence bags” that deliver a concentrated payload of fungal products to host effector cells and tissues.