FabG, an NADPH-dependent 3-ketoacyl reductase of Pseudomonas aeruginosa, provides precursors for medium-chain-length poly-3-hydroxyalkanoate biosynthesis in Escherichia coli

Escherichia coli hosts expressing fabG of Pseudomonas aeruginosa showed 3-ketoacyl coenzyme A (CoA) reductase activity toward R-3-hydroxyoctanoyl-CoA. Furthermore, E. coli recombinants carrying the poly-3-hydroxyalkanoate (PHA) polymerase-encoding gene phaC in addition to fabG accumulated medium-chain-length PHAs (mcl-PHAs) from alkanoates. When E. coli fadB or fadA mutants, which are deficient in steps downstream or upstream of the 3-ketoacyl-CoA formation step during beta-oxidation, respectively, were transformed with fabG, higher levels of PHA were synthesized in E. coli fadA, whereas similar levels of PHA were found in E. coli fadB, compared with those of the corresponding mutants carrying phaC alone. These results strongly suggest that FabG of P. aeruginosa is able to reduce mcl-3-ketoacyl-CoAs generated by the beta-oxidation to 3-hydroxyacyl-CoAs to provide precursors for the PHA polymerase.