Fungal polysaccharides are altered by lyophilization resulting in decreased antibody binding

Abstract

The capsule of Cryptococcus neoformans is unique in the fungal kingdom. Its hydrophilic nature and relative neutrality have complicated characterization (1). Even the synthesis of the polysaccharide capsule, being nutrient costly yet induced by nutrient poor conditions, seems counter intuitive. While the encapsulation of cryptococcal species is unique, the secretion of its signature polysaccharide – glucuronoxylomannan (GXM) – is not. Histoplasma capsulatum (2), Paracoccidioides brasiliensis (3), and many of the Trichosporonaceae family including Trichosporon asahii, Trichosporon inkin, Apiotrichum montevideense, Trichosporon japonicum, Trichosporon faecale, Trichosporon ovoides, Cutaneotrichosporon debeurmannianum, and Cutaneotrichosporon arboriformis all produce GXM‐like polymers (4, 5). Even basidiomycete fungal symbionts of many lichens Tremella and Cyphobasidium are predicted to produce a GXM‐like polysaccharide (6). As we investigate the role these glycans play in other fungal species it is important that physicochemical properties be conserved. Recent work by our group has shown that the lyophilization of polysaccharide preparations alters them such that antibody binding is reducing, suggesting that these changes have a functional effect. The difference between the polysaccharides before and after lyophilization is stark. Natively isolated polysaccharide preparations have ordered polymers that form small, loosely packed aggregates and contain extracellular vesicles. However, after lyophilization polymers are disordered and form dense rosette‐like aggregates and are absent extracellular vesicles. In addition, lyophilized and re‐solubilized samples allowed to incubate for 28 days did not return to the pre‐lyophilized, native state. This suggests that the changes induced by lyophilization many not be reversible. As we explore the role of these glycans in host‐microbe interactions, we need to consider the effects of lyophilization on the biological and immunological attributes of polysaccharides.