Aryl-aldehyde formation in fungal polyketides: discovery and characterization of a distinct biosynthetic mechanism.

Aryl-aldehydes are a common feature in fungal polyketides, which are considered to be exclusively generated by the R domain of nonreducing polyketide synthases (NR-PKSs). However, by cloning and heterologous expression of both cryptic NR-PKS and nonribosomal peptide synthase (NRPS)-like genes from Aspergillus terreus in Saccharomyces cerevisiae, we identified a distinct mechanism for aryl-aldehyde formation in which a NRPS-like protein activates and reduces an aryl-acid produced by the accompanying NR-PKS to an aryl-aldehyde. Bioinformatics study indicates that such a mechanism may be widely used throughout the fungi kingdom.