Direct conversion of glucose to malate by synthetic metabolic engineering

Synthetic metabolic engineering enables us to construct an in vitro artificial synthetic pathways specialized for chemical manufacturing through the simple heat-treatment of the recombinant mesophiles having thermophilic enzymes, followed by rational combination of those biocatalytic modules. In this work, we constructed a synthetic pathway capable of direct conversion of glucose to malate. The reversible carboxylation of pyruvate catalyzed by a malic enzyme derived from Thermococcus kodakarensis (TkME) (ΔG°′ = +7.3 kJ mol−1) was coupled with a thermodynamically favorable non-ATP-forming Embden–Meyerhof pathway to balance the consumption and regeneration of redox cofactors and to shift the overall equilibrium toward malate production (glucose + 2HCO3− + 2H → 2 malate + 2H2O; ΔG°′ = −121.4 kJ mol−1). TkME exhibited both pyruvate carboxylation (malate-forming) and pyruvate reduction (lactate-forming) activities. By increasing HCO3− concentration, the reaction specificity could be redirected to malate production. As a result, the direct conversion of glucose to malate was achieved with a molar yield of 60%.

► An in vitro metabolic pathway for conversion of glucose to malate was constructed. ► Reversible carboxylation was coupled with a non-ATP-forming glycolysis pathway. ► Thermococcus malic enzyme showed both lactate-forming and malate-forming activities. ► Reaction specificity was redirected to malate by increasing the HCO3− concentration.