naphthoquinones and scytolone

Sporothrix schenckii is a human pathogen that causes sporotrichosis, an important cutaneous mycosis with a worldwide distribution. It produces dark-brown conidia, which infect the host. We found that S. schenckii synthesizes melanin via the 1,8-dihydroxynaphthalene pentaketide pathway. Melanin biosynthesis in the wild type was inhibited by tricyclazole, and colonies of the fungus were reddish brown instead of black on tricyclazole-amended medium. Two melanin-deficient mutant strains were analyzed in this study: an albino that produced normal-appearing melanin on scytalone-amended medium and a reddish brown mutant that accumulated and extruded melanin metabolites into its medium. Scytalone and flaviolin obtained from cultures of the reddish brown mutant were identified by thin-layer chromatography, high-performance liquid chromatography, and UV spectra. Transmission electron microscopy showed an electron-dense granular material believed to be melanin in wild-type conidial cell walls, and this was absent in conidial walls of the albino mutant unless the albino was grown on a scytalone-amended medium. Melanized cells of wild-type S. schenckii and the albino grown on scytalone-amended medium were less susceptible to killing by chemically generated oxygen- and nitrogen-derived radicals and by UV light than were conidia of the mutant strains. Melanized conidia of the wild type and the scytalone-treated albino were also more resistant to phagocytosis and killing by human monocytes and murine macrophages than were unmelanized conidia of the two mutants. These results demonstrate that melanin protects S. schenckii against certain oxidative antimicrobial compounds and against attack by macrophages.

Topics: Adult; Animals; Free Radicals; Humans; Macrophages, Peritoneal; Male; Melanins; Mice; Mice, Inbred BALB C; Monocytes; Mutation; Naphthols; Naphthoquinones; Respiratory Burst; Spores, Fungal; Sporothrix; Thiazoles; Ultraviolet Rays

Melanin biosynthesis in the human pathogen Wangiella dermatitidis was inhibited by tricyclazole, causing pentaketide melanin metabolites to accumulate in the cultures. One of these metabolites, scytalone, was racemic and thus different than the (+)-enantiomer from Verticillium dahliae. An albino mutant of W. dermatitidis metabolized scytalone to a pigment ultrastructurally identical to wild-type melanin. Cell-free homogenates of the wild type carried out typical reductive and dehydrative reactions with known melanin intermediates and the reductive reactions were inhibited by tricyclazole. Other reductive and dehydrative reactions that utilize flaviolin and 2-hydroxyjuglone were studied anaerobically with homogenates from both the wild type and the albino mutant. The homogenates converted flaviolin to 5-hydroxyscytalone and products identical to those obtained from 2-hydroxyjuglone. The albino, in culture, carried out the same reactions with 2-hydroxyjuglone but metabolized flaviolin to a number of unknown colored products apparently through oxidative reactions. Similarities between the melanin pathway and the flaviolin and 2-hydroxyjuglone branch pathways are discussed and tricyclazole is shown to inhibit reductive reactions with naphthols in the three pathways.

Topics: Melanins; Mitosporic Fungi; Naphthols; Naphthoquinones; Optical Rotation; Thiazoles

Melanin synthesis in the dematiaceous, polymorphic hyphomycete Wangiella dermatitidis, a human pathogen, was investigated by biochemical and physiological techniques. Mutants with a decrease or loss in melanin synthesis were induced and isolated. Melanin precursors were obtained from the mutants, purified, and then identified by comparison with authentic compounds from Verticillium dahliae . Isolation of scytalone , vermelone , flaviolin , and 1,8- dihydroxynaphthalene from the mutants of Wangiella dermatitidis, and cross-feeding of the mutants with those of Verticillium dahliae indicated that melanin synthesis in this organism took place by the pentaketide pathway. Melanin that formed in cell walls of an albino mutant treated with scytalone was identified in appearance to that in cell walls of the wild-type strain. This also suggested that pentaketide synthesis of melanin occurred in the fungus.

Topics: Melanins; Mitosporic Fungi; Mutation; Naphthols; Naphthoquinones; Species Specificity