The Ketosynthase Domain Controls Chain Length in Mushroom Oligocyclic Polyketide Synthases.

The nonreducing iterative type I polyketide synthases (NR-PKSs) CoPKS1 and CoPKS4 of the webcap mushroom Cortinarius odorifer share 88 % identical amino acids. CoPKS1 almost exclusively produces a tricyclic octaketide product, atrochrysone carboxylic acid, whereas CoPKS4 shows simultaneous hepta- and octaketide synthase activity and also produces the bicyclic heptaketide 6-hydroxymusizin. To identify the region(s) controlling chain length, four chimeric enzyme variants were constructed and assayed for activity in Aspergillus niger as heterologous expression platform. We provide evidence that the ß-ketoacyl synthase (KS) domain determines chain length in these mushroom NR-PKSs, even though their KS domains differ in only ten amino acids. A unique proline-rich linker connecting the acyl carrier protein with the thioesterase domain varies most between these two enzymes but is not involved in chain length control.

Efficient heterologous production of atrochrysone carboxylic acid-related polyketides in an Aspergillus oryzae host with enhanced malonyl-coenzyme A supply.

We recently developed an Aspergillus oryzae strain in which malonyl-coenzyme A (CoA) supply is strengthened by the deletion of snfA and SCAP as an efficient host to produce a plant polyketide, curcumin. Here, we examined the effectiveness of this strain in producing another polyketide, atrochrysone carboxylic acid (ACA), which is synthesized from eight molecules of malonyl-CoA using an iterative type I polyketide synthase, ACA synthase (ACAS), and atrochrysone carboxyl ACP thioesterase (ACTE) in Aspergillus terreus. When ACAS and ACTE were introduced, the A. oryzae ΔsnfAΔSCAP strain produced approximately four times more ACA-related polyketides than did the control strain expressing both genes. This result further demonstrated the availability of the A. oryzae ΔsnfAΔSCAP strain for heterologous polyketide production.