Functional analysis of fungal polyketide biosynthesis genes

Abstract

Fungal polyketides have huge structural diversity from simple aromatics to highly modified complex reduced-type compounds. Despite such diversty, single modular iterative type I polyketide synthases (iPKSs) are responsible for their carbon skeleton construction. Using heterologous expression systems, we have studied on ATX, a 6-methylsalicylic acid synthase from Aspergillus terreus as a model iPKS. In addition, iPKS functions involved in fungal spore pigment biosynthesis were analyzed together with polyketide-shortening enzymes that convert products of PKSs to shorter ketides by hydrolytic C-C bond cleavage. In our studies on reducing-type iPKSs, we cloned and expressed PKS genes, pksN, pksF, pksK and sol1 from Alternaria solani. The sol gene cluster was found to be involved in solanapyrone biosynthesis and sol5 was identified to encode solanapyrone synthase, a Diels-Alder enzyme. Our fungal PKS studies were further extended to identify the function of PKS-nonribosomal peptide synthase involved in cyclopiazonic acid biosynthesis.

Comparison of Expression of Secondary Metabolite Biosynthesis Cluster Genes in Aspergillus flavus, A. parasiticus, and A. oryzae

“…Also, the gene for cluster 27 PKS, which was shown to be necessary for most sclerotial pigmentation [19], only is expressed highly in cultures undergoing sclerotial formation ( A. flavus CA42 in Table S1). Several of the non-reducing PKS genes that are differentially expressed in the different isolates, based on homology to genes in other fungi [20], are predicted to be associated with production of polyketides required for pigment formation, for example, those in clusters 5, 36, 39 and 42. The gene for the DMATS in cluster 19 was expressed at a high RPKM level in most isolates while the GGPS of cluster 37 (an NRPS cluster) was expressed at the highest level in NRRL3357.…”

New insights into the formation of fungal aromatic polyketides

“…Based on the new study and previous results, a unified biosynthetic path was proposed, in which acetyl-CoA is incorporated into the hexaketide acetyl-THN ( 13 ), and an Ayg1p-mediated hydrolytic chain shortening reaction could occur, as had been found for YWA1 (Fig 3). Indeed, a knockout of the Ayg1p homologue in Wangiella dermatitidis later confirmed that a PKS1 homologue produced acetyl-THN 94 , and that the enzyme was capable of catalyzing the retro-Claisen reaction in vitro 95 . The same phenomenon has yet to be confirmed experimentally for the C. lagenarium PKS1 system.…”

Lovastatin, Compactin, and Related Anticholesterolemic Agents

“…The PKS requires the participation of an endogenous enoyl reductase protein (LovC or MlcG) to generate the desired nonaketide intermediates. (For a recent review of fungal secondary metabolites that use similar machinery, see Boettger and Hertweck [ 64 ] and for in depth reviews on fungal PKSs, see Cox and Simpson [ 65 ] and Fujii [ 66 ].) Remarkable programming steps are involved in ensuring correct domain use during each round of chain elongation.…”