Functional expression of the Aspergillus flavus PKS–NRPS hybrid CpaA involved in the biosynthesis of cyclopiazonic acid

Abstract

α-Cyclopiazonic acid (CPA) is an indole tetramic acid mycotoxin. Based on our identification of the polyketide synthase–nonribosomal peptide synthase (PKS–NRPS) hybrid gene cpaA involved in cyclopiazonic acid biosynthesis in Aspergillus fungi, we carried out heterologous expression of Aspergillus flavus cpaA under α-amylase promoter in Aspergillus oryzae and identified its sole product to be the CPA biosynthetic intermediate cyclo-acetoacetyl- l-tryptophan (cAATrp). This result rationalized that the PKS–NRPS hybrid enzyme CpaA catalyzes condensation of the diketide acetoacetyl-ACP formed by the PKS module and l-Trp activated by the NRPS module. This CpaA expression system provides us an ideal platform for PKS–NRPS functional analysis, such as adenylation domain selectivity and product releasing mechanism.