Binding of the Wheat Germ Lectin to Cryptococcus neoformans Suggests an Association of Chitinlike Structures with Yeast Budding and Capsular Glucuronoxylomannan

Abstract

ABSTRACT The capsule of Cryptococcus neoformans is a complex structure whose assembly requires intermolecular interactions to connect its components into an organized structure. In this study, we demonstrated that the wheat germ agglutinin (WGA), which binds to sialic acids and β-1,4- N -acetylglucosamine (GlcNAc) oligomers, can also bind to cryptococcal capsular structures. Confocal microscopy demonstrated that these structures form round or hooklike projections linking the capsule to the cell wall, as well as capsule-associated structures during yeast budding. Chemical analysis of capsular extracts by gas chromatography coupled to mass spectrometry and high-pH anion-exchange chromatography suggested that the molecules recognized by WGA were firmly associated with the cell wall. Enzymatic treatment, competition assays, and staining with chemically modified WGA revealed that GlcNAc oligomers, but not sialic acids, were the molecules recognized by the lectin. Accordingly, treatment of C. neoformans cells with chitinase released glucuronoxylomannan (GXM) from the cell surface and reduced the capsule size. Chitinase-treated acapsular cells bound soluble GXM in a modified pattern. These results indicate an association of chitin-derived structures with GXM and budding in C. neoformans , which may represent a new mechanism by which the capsular polysaccharide interacts with the cell wall and is rearranged during replication.