Improving Polyketide Production By Screening Heterologously Expressed Synthetic Propionyl-CoA Carboxylases

Polyketides are valuable natural products that have antibacterial, anticancer, and immunosuppressant activities. Many bacterial polyketides are produced by modular polyketide synthases (PKS) in an assembly line fashion from simple two-carbon monomer inputs. Two PKS pathways, encoding erythromycin and epothilone, have been heterologously expressed in Escherichia coli (E. coli), but at low yields (0.001-20mg/L). We aimed to improve E. coli as a host for polyketide production by providing more monomer inputs for PKS assembly lines. For many polyketides, the extender monomer is methylmalonyl-CoA and the enzyme that provides it is propionyl-CoA carboxylase (PCC). We used as our test system a strain of E. coli harboring the 6-deoxyerythronolide B synthase PKS, which produces the erythromycin polyketide. We designed and synthesized DNA encoding 20 PCC gene homologs from different species and built 20 versions of the E. coli polyketide-producing strain, each harboring a different PCC homolog. We observed variability in polyketide production amongst the 20 strains, and identified optimal PCC homologs. These results may be useful for improving E. coli as a host for heterologous expression of orphan PKSs, as well as for engineering polyketides and producing novel unnatural products.