Chitin deacetylase 3 of Cryptococcus neoformans produces chitosans with low degree and random pattern of acetylation

The fungal pathogen Cryptococcus neoformans poses a significant global health concern, accounting for more than 100,000 fatalities among individuals with AIDS alone every year. In contrast to other Basidiomycetes, C. neoformans actively deacetylates the chitin in its cell wall to chitosans. The deacetylation reaction is catalyzed by four chitin deacetylases (CnCDAs 1-4), presumably to evade the chitin-triggered host immunity. In this study, we conducted a comprehensive in vitro characterization of recombinant CnCDA3, revealing a preference for deacetylated units at its -1 subsite, higher activity on longer substrates, and the generation of random acetylation patterns in polymer deacetylation (and N-acetylation) products. In combination with in silico modeling of all CnCDAs, the experimental results suggest that the function of CnCDA3 in vivo may be to further deacetylate cell wall chitosans initially produced from nascent chitin chains by the action of other membrane-associated CnCDAs. Deeper understanding of the actions of these enzymes involved in fungal virulence may facilitate the urgently needed improvement in therapies and the development of effective cell-based vaccines against cryptococcal infections.