Bioengineering polyketide precursor supply in native and heterologous hosts

The complexity of polyketides is partly due to the large pool of diverse starter units, while the extender unit variety was known to be mostly limited to the shunt products malonyl- and methylmalonyl-CoA. Over the last years of polyketide research new PKS extender units with various substitutions at the C2 position have been identified. They are derived from α,β-unsaturated acyl-CoA precursors via a reductive carboxylation reaction carried out by a crotonyl-CoA reductase/carboxylase (CCR). We studied gene regulation of the first characterized CCR-derived extender unit, chloroethylmalonyl-CoA.^[1] This halogenated moiety highly contributes to the bioactivity of salinosporamide A, a potent proteasome inhibitor. The modularity of precursor biosynthesis can further be explored for engineering efforts. In one example, we isolated a pathway for the unusual extender unit isobutyrylmalonyl-CoA and successfully implemented its gene cassette into the heterologous FK506 pathway to biosynthesize an unnatural analog with increased bioactivity.^[2] The implementation of various precursor supply pathways is a prerequisite for heterologous polyketide biosynthesis in other non-PKS containing hosts, such as the industrial producer S. cerevisiae. Current efforts are underway to evaluate and engineer S. cerevisiaeas a eukaryotic polyketide production host.

1.         Lechner, A.; Eustaquio, A. S.; Gulder, T. A.; Hafner, M.; Moore, B. S., Selective overproduction of the proteasome inhibitor salinosporamide A via precursor pathway regulation. Chem Biol 2011, 18 (12), 1527-36.

2.         Lechner, A.; Wilson, M. C.; Ban, Y. H.; Hwang, J.-y.; Yoon, Y. J.; Moore, B. S., Designed Biosynthesis of 36-Methyl-FK506 by Polyketide Precursor Pathway Engineering. ACS Synthetic Biology 2012.