Solid-state NMR spectroscopy identifies three classes of lipids inC. neoformansmelanized cell walls and whole fungal cells

Abstract

AbstractA primary virulence-associated trait of the opportunistic fungal pathogenCryptococcus neoformansis the production of melanin pigments that are deposited into the cell wall and interfere with the host immune response. Previously, our solid-state NMR studies of isolated melanized cell walls (melanin ‘ghosts’) revealed that the pigments are strongly associated with lipids, but their identities, origins, and potential roles were undetermined. Herein, we exploited spectral editing techniques to identify and quantify the lipid molecules associated with pigments in melanin ghosts. The lipid profiles were remarkably similar in wholeC. neoformanscells, grown under either melanizing or non-melanizing conditions; triglycerides (TGs), sterol esters (SEs) and polyisoprenoids (PPs) were the major constituents. Although no quantitative differences were found between melanized and non-melanized cells, melanin ghosts were relatively enriched in SEs and PPs. In contrast to lipid structures reported during early stages of fungal growth in nutrient-rich media, variants found herein could be linked to nutrient stress, cell aging, and subsequent production of substances that promote chronic fungal infections. The fact that TGs and SEs are the typical cargo of lipid droplets suggests that these organelles could be connected toC. neoformansmelanin synthesis. Moreover, the discovery of PPs is intriguing because dolichol is a well-established constituent of human neuromelanin. The presence of these lipid species even in non-melanized cells suggests that they could be produced constitutively under stress conditions in anticipation of melanin synthesis. These findings demonstrate thatC. neoformanslipids are more varied compositionally and functionally than previously recognized.