|Wheeler, Michael - Mike|
Submitted to: Eukaryotic Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2008
Publication Date: 8/1/2008
Citation: Wheeler, M.H., Abramczyk, D., Puckhaber, L.S., Naruse, M., Ebizuka, Y., Fujii, I., Szaniszlo, P.J. 2008. New biosynthetic step in the melanin pathway of Wangiella (Exophiala) dermatitidis: Evidence for 2-Acetyl-1,3,6,8-tetrahydroxynaphthalene as a novel precursor. Eukaryotic Cell 7:1699-1711. Interpretive Summary: Some plant and animal fungal pathogens contain a black pigment called melanin that helps their spores survive in various environments. Early steps in the biosynthesis of this pigment by the human pathogen known as Wangiella dermatitidis are poorly understood. In the present study, we discovered two early steps in the biosynthesis of the black melanin, one leading to the production of a known compound and the other leading to production of a newly defined compound. The discovery of each compound provides additional information that can be used to understand the biosynthesis of the pigment and possibly help control disease caused by this and other melanin-producing pathogens.
Technical Abstract: The predominant cell wall melanin of Wangiella dermatitidis, a black fungal pathogen of humans, is synthesized from 1,8-dihydroxynaphthalene (D2HN). An early precursor, 1,3,6,8-tetrahydroxynaphthalene (T4HN), in the pathway leading to D2HN is reportedly produced as a pentaketide directly by an iterative type I polyketide synthase (PKS). In contrast, the bluish-green pigment in Aspergillus fumigatus is produced after the enzyme Ayg1p converts the PKS product, heptaketideYWa1, to T4HN. Previously, we created a new melanin-deficient mutant of W. dermatitidis, WdBrm1, by random molecular insertion. From this strain, the altered gene WdYG1 was cloned by a marker rescue strategy and found to encode WdYg1p, an ortholog of Ayg1p. In the present study, two gene replacement mutants devoid of the complete WdYG1 gene were derived to eliminate the possibility that the phenotype of WdBrm1 was due to other mutations. Characterization of the new mutants showed they were phenotypically identical to WdBrm1. Chemical analyses of mutant cultures demonstrated that melanin biosynthesis was blocked, resulting in the accumulation of 2-acetyl-1,3,6,8-tetrahydroxynaphthalene (AT4HN) and its oxidative product 3-acetylflaviolin in the culture media. When given to an albino W. dermatitidis strain with an inactivated WdPKS1 gene, AT4HN was mostly oxidized to 3-acetylflaviolin and deacetylated to flaviolin. Under reduced oxygen conditions, cell-free homogenates of the albino converted AT4HN to D2HN. This is the first report of evidence that the hexaketide AT4HN is a melanin precursor for T4HN in W. dermatitidis.