Structural features and roles of O-glycans in the secretion, stability, and immunogenicity of Cryptococcus neoformans...

The human pathogenic yeast-Cryptococcus neoformans-assembles two types of O-glycans on its proteins: major O-glycans lacking xylose and minor xylose-containing O-glycans, mediated by Ktr3 and Cap6 mannosyltransferases, respectively. In this study, we examined the effect of O-glycan on two glycosylphosphatidylinositol (GPI)-anchored mannoproteins, MP88 and chitin deacetylase 1 (Cda1), on proteolytic stability and host-cell interactions. Expression analysis of Cda1 in the O-glycans mutant strains revealed the aberrant cleavage of Cda1 in the absence of extended major O-glycans. The GPI-anchorless, C-terminal His-tagged proteins expressed in ktr3∆ and cap6∆ were purified as extracellular forms. KTR3 deletion led to the accumulation of truncated O-glycans with single mannose residues and an increased xylose-containing glycans. Dendritic cells exposed to the MP88 and Cda1 proteins purified from the cap6∆ exhibited reduced IL-6 secretion compared to those treated with wild-type or ktr3∆ proteins. Additionally, mice immunized with Cda1 from ktr3∆ produced significantly more anti-Cda1 antibodies than those immunized with wild-type Cda1, consistent with enhanced IL-6 secretion. These results underscore the contribution of xylose residues in O-glycans to the immune response. Understanding the structure and function of O-glycans assembled on immunogenic proteins, particularly their influence on immune interactions, offers insights for designing vaccines against fungal pathogens.