Biosynthetic Study on Antihypercholesterolemic Agent Phomoidride: General Biogenesis of Fungal Dimeric Anhydrides

Abstract

To elucidate the general biosynthetic pathway of fungal dimeric anhydrides, a gene cluster for the biosynthesis of the antihy-percholesterolemic agent phomoidride was identified by heterologous expression of candidate genes encoding the highly reducing polyketide synthase, alkylcitrate synthase (ACS), and alkylcitrate dehydratase (ACDH). An in vitro analysis of ACS and ACDH revealed that they give rise to anhydride monomers. Based on the established monomer biosynthesis, we propose a general biogenesis of dimeric anhydrides involving a single donor unit and four acceptor units.

Heterologous Production of Fungal Maleidrides Reveals the Cryptic Cyclization Involved in their Biosynthesis

“…The polyketide is presumably released from the PKS by the BfL1 hydrolase, although it is not yet known whether this is as the free acid or as a CoA‐thiolester. This result contrasts with the recently reported work of Oikawa, who showed that the hydrolase did not appear to be required in the case of a Talaromyces PKS 18. However it is known that some iterative fungal PKSs, for example the squalestatin tetraketide synthase,23 can release polyketides without the requirement for a dedicated thiolesterase.…”

“…Heterologous expression experiments utilizing the three genes from one of the T. stipitatus BGCs allowed the isolation of a longer‐chain decarboxylated monomer. These experiments confirm the polyketide/oxaloacetate origin of maleidride monomers 18. However the proteins responsible for the key cyclisation reaction necessary for maleidride biosynthesis remain unkown.…”

“…Oikawa and co‐workers suggested that the longer‐chain decarboxylated monomer isolated from their heterologous expression experiments is produced by an adventitious native decarboxylase 18. Our experiments have previously identified the natural product 10 by comparing its LCMS characteristics with data collected for the synthetic homologue, which was also observed to decarboxylate spontaneously to give 9 .…”

“…Based on previous biosynthetic investigations, our discovery of the byssochlamic acid pathway, and research conducted by Oikawa and co‐workers,18 we now propose a general biosynthetic route to maleidrides (Scheme 1). In each maleidride pathway, the initial steps are common, with potential differences including polyketide chain length and pattern of reduction.…”

“…In a recent investigation of the biosynthesis of phomoidride A ( 4 ), Oikawa and co‐workers also identified a BGC containing an hrPKS, a citrate‐synthase‐like enzyme, and a methylcitrate dehydratase, as well as the two maleidride‐type BGCs from Talaromyces stipitatus 18. Heterologous expression experiments utilizing the three genes from one of the T. stipitatus BGCs allowed the isolation of a longer‐chain decarboxylated monomer.…”