Vesicle-associated melanization in Cryptococcus neoformans

1 Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA 2 Departamento de Biologia Celular, Universidade de Brasília, Brazil 3 Laboratório de Estudos Integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-590, Brazil Recently, several pathogenic fungi were shown to produce extracellular vesicles that contain various components associated with virulence. In the human pathogenic fungus Cryptococcus neoformans , these components included laccase, an enzyme that catalyses melanin synthesis. Spherical melanin granules have been observed in the cell wall of C. neoformans . Given that melanin granules have dimensions that are comparable to those of extracellular vesicles, and that metazoan organisms produce melanin in vesicular structures known as melanosomes, we investigated the role of vesicles in cryptococcal melanization. Extracellular vesicles melanized when incubated with the melanin precursor L -3,4-dihydroxyphenylalanine ( L -DOPA). The kinetics of substrate incorporation into cells and vesicles was analysed using radiolabelled L -DOPA. The results indicated that substrate incorporation was different for cells and isolated vesicles. Acid-generated melanin ghosts stained with lipophilic dyes, implying the presence of associated lipid. A model for C. neoformans melanization is proposed that accounts for these observations and provides a mechanism for the assembly of melanin into relatively uniform spherical particles stacked in an orderly arrangement in the cell wall. Correspondence Arturo Casadevall casadeva{at}aecom.yu.edu Abbreviations: DOPA, 3,4-dihydroxyphenylalanine; QELS, quasi-elastic light scattering; TEM, transmission electron microscopy These authors contributed equally to this work. Present address: Department of Natural Sciences, Baruch College, 17 Lexington Avenue, New York, NY 10010, USA. Present Address: Laboratório de Biotecnologia (LABIO), Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Av. Nossa Senhora das Graças 50, Xerém, Rio de Janeiro 25 250 020, Brazil.