Aspergillus fumigatus alb1 encodes naphthopyrone synthase when expressed in Aspergillus oryzae

Conidial pigment biosynthesis is an important virulence factor in Aspergillus fumigatus, a human fungal pathogen. Involvement of DHN-melanin pathway in the biosynthesis of A. fumigatus conidial pigment implies that the Alb1p polyketide synthase (PKS) is a 1,3,6, 8-tetrahydroxynaphthalene (T4HN) synthase. The Alb1p, however, shows higher sequence similarity to a naphthopyrone synthase than to a T4HN synthase. To clarify the function of Alb1p, the alb1 gene was overexpressed in a heterologous host Aspergillus oryzae. The Alb1p PKS product in this heterologous expression system was identified as heptaketide naphthopyrone instead of pentaketide T4HN. The data suggest that Alb1p is a naphthopyrone synthase.