Aspergillus oryzae CsyB Catalyzes the Condensation of Two {beta}-Ketoacyl-CoAs to Form 3-Acetyl-4-hydroxy-6-alkyl-{alpha}-pyrone [Microbiology]

June 3rd, 2014 by Hashimoto, M., Koen, T., Takahashi, H., Suda, C., Kitamoto, K., Fujii, I.

The type III polyketide synthases (PKSs) from fungi produce a variety of secondary metabolites including pyrones, resorcinols, and resorcylic acids. We previously reported that CsyB from Aspergillus oryzae forms α-pyrone csypyrone B compounds when expressed in A. oryzae. Feeding experiments of labeled acetates indicated that a fatty acyl starter is involved in the reaction catalyzed by CsyB. Here we report the in vivo and in vitro reconstitution analysis of CsyB. When CsyB was expressed in E. coli, we observed the production of 3-acetyl-4-hydroxy-α-pyrones with saturated or unsaturated straight aliphatic chains of C9 ~ C17 in length at the 6-position. Subsequent in vitro analysis using recombinant CsyB revealed that CsyB could accept butyryl-CoA as a starter substrate, and malonyl-CoA and acetoace-tyl-CoA as extender substrates to form 3-acetyl-4-hydroxy-6-propyl-α-pyrone. CsyB also afforded dehydroacetic acid from two molecules of acetoacetyl-CoA. Furthermore, synthetic N-acetylcysteamine thioester of β-ketohexanoic acid was converted to 3-butanoyl-4-hydroxy-6-propyl-α-pyrone by CsyB. These results therefore confirmed that CsyB catalyzed the synthesis of β-ketoacyl-CoA from the reaction of the starter fatty acyl CoA thioesters with malonyl-CoA as the extender through decarboxylative condensation, and further coupling with acetoacetyl-CoA to form 3-acetyl-4-hydroxy-6-alkyl-α-pyrone (AcAP). CsyB is the first type III PKS that synthesizes AcAP by catalyzed the coupling of two β-ketoacyl-CoAs.
  • Posted in Journal of Biological Chemistry, Publications
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