Proteins associated with Cryptococcus spp. extracellular polysaccharides are implicated in virulence, capsule integrity, and biofilm formation.

Abstract

Cryptococcus neoformans and Cryptococcus gattii are pathogenic fungi comprising species complexes that are the etiological agents of cryptococcosis. Both fungal species complexes possess a variety of virulence factors that include a polysaccharide capsule, melanin production, enzymes, and the release of polysaccharides. In this study, we characterized the proteins associated with cryptococcal polysaccharides and analyzed their function by studying mutants deficient in their expression. Mass spectrometry analysis of exopolysaccharide fractions revealed 62 proteins, many of which were previously uncharacterized. Analysis of capsule size, structure, and integrity in protein-deficient mutants allowed us to identify four proteins, which we named Extracellular Polysaccharide Related proteins (Exa1-4), and whose absence affected proper capsule assembly and EPS release. In summary, cryptococcal exopolysaccharide is associated with proteins that are implicated in virulence, capsular integrity, and biofilm formation. Our results associated new phenotypes for four previously unknown genes and show that the filtered polysaccharide preparations are a rich source of proteins that can inform capsular assembly, virulence, and immunological studies.