title: Vesicle-associated melanization in Cryptococcus neoformans.
abstract: 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.
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Helene C
authors.initials: HC
authors.lastname: Eisenman
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Susana
authors.initials: S
authors.lastname: Frases
authors.affiliation: Departamento de Biologia Celular, Universidade de Brasília, Brazil.|Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: André M
authors.initials: AM
authors.lastname: Nicola
authors.affiliation: 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.
authors.forename: Marcio L
authors.initials: ML
authors.lastname: Rodrigues
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Arturo
authors.initials: A
authors.lastname: Casadevall
mesh_terms: D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure; D003455:Cryptococcus neoformans / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D006801:Humans; D007980:Levodopa / Q000378:metabolism; D008081:Liposomes; D008543:Melanins / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D014774:Virulence
chemical_list: D008081:Liposomes; D008543:Melanins; D007980:Levodopa