Microstructure of cell wall-associated melanin in the human pathogenic fungus Cryptococcus neoformans

Area of Science:

• Mycology
• Biophysics
• Structural Biology

Background:

• Melanin is a key virulence factor in pathogenic fungi like Cryptococcus neoformans.
• Fungal melanin, particularly from C. neoformans, forms cell-shaped hollow structures known as melanin ghosts.

Purpose of the Study:

• To elucidate the structural characteristics of Cryptococcus neoformans melanin ghosts.
• To investigate the porosity and surface morphology of melanin ghosts.
• To explore the potential antifungal mechanisms related to melanin structure.

Main Methods:

• Atomic force microscopy (AFM)
• Scanning electron microscopy (SEM)
• Transmission electron microscopy (TEM)
• Nuclear magnetic resonance (NMR) cryoporometry

Main Results:

• Melanin ghosts exhibit a surface covered with granular particles (40-130 nm in diameter).
• The melanin structure consists of multiple concentric layers.
• NMR cryoporometry revealed pores within the 1-4 nm range and some larger pores (~30 nm).
• Antibody binding to melanin reduced the measured pore volume, suggesting a functional interaction.

Conclusions:

• A structural model for cryptococcal melanin is proposed, featuring layered melanin granules.
• The proposed structure has implications for understanding fungal cell division and cell wall remodeling.
• Insights into melanin structure may facilitate the discovery of new antifungal drugs.