|Wheeler, Michael - Mike|
Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2001
Publication Date: N/A
Technical Abstract: Aspergillus fumigatus synthesizes its bluish-green conidial pigment via a pentaketide pathway similar to the 1,8-dihydroxynaphthalene (DHN)-melanin pathway. Biosynthesis of the conidial polyketides pigment has been shown to significantly influence virulence of A. fumigatus in a murine model. Our previous studies showed that a cluster of six genes is required for conidial pigment biosynthesis. Polyketide synthase (Alb1p), THN reductase (Arp2p) and scytalone dehydratase (Arp1p) are reported to catalyze the first three steps of the pentaketide pathway. However, the function of AYG1 (Aspergillus yellowish-green 1), one of the six-clustered genes, remains unknown. Fungal polyketides melanins are mostly derived from the pentaketide precursor 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) and the protein used for synthesis of the precursor is usually a pentaketide synthase. However, A. fumigatus uses a heptaketide synthase, Alb1p, which produces a heptaketide instead of a pentaketide. Involvement of a heptaketide synthase in the pentaketide melanin pathway is fundamentally different from the known fungal DHN-melanin pathway. In this study, we found that disruption of AYG1 in A. fumigatus failed to accumulate 1,3,6,8-THN. Genetic and biochemical analyses indicated that Ayg1p catalyzes a novel biosynthetic step between Alb1p and Arp2p. Finally, reactions using the crude Ayg1p protein extract showed that Ayg1p enzymatically converted the heptaketide product of Alb1p to 1,3,6,8-THN by shortening the carbon skeleton. Thus we conclude that Ayg1p facilitates the participation of a heptaketide synthase in a pentaketide melanin pathway via a polyketides shortening mechanism.