Figure 1.

Melanins in A. fumigatus. (A) Pyomelanin: the tyrosine degradation pathway and genomic organization of the genes involved in tyrosine degradation and pyomelanin formation. The degradation of tyrosine starts with the formation of p-hydroxyphenylpyruvate (pHPP), which is then converted to HGA by the p-hydroxyphenylpyruvate dioxygenase (HppD). HGA is either degraded enzymatically by maleylacetoacetate isomerase (MaiA) and fumarylacetoacetate hydrolase (FahA) to fumarate and acetoacetate, compounds of the primary metabolism, or homogentisate polymerizes oxidatively to pyomelanin. Pyomelanin production is shown in supernatants of different A. fumigatus strains cultivated in minimal medium with addition of tyrosine. (B) DHN melanin: the DHN-melanin biosynthesis pathway and genomic organization of the genes involved in DHN-melanin biosynthesis [adapted from Langfelder et al. (2003) and Tsai et al. (2001)]. Starting from acetyl-CoA and malonyl-CoA, PksP produces the heptaketide naphthopyrone YWA1, which is shortened by hydrolytic activity of Ayg1 to 1,3,6,8-tetrahydroxy naphthalene (THN). This pentaketide undergoes reduction, mediated by the THN reductase Arp2 and dehydration by the scytalone dehydratase Arp1. Finally, the laccase Abr2 catalyses oxidative polymerization of 1,8-DHN to form the final pigment (Tsai et al., 2001; Fujii et al., 2004; Sugareva et al., 2006). The picture shows the color of conidia of different DHN-melanin biosynthesis mutants.