(727c) Pathway and Host Engineering for Biosynthesis of 3-Hydroxy-γ-Butyrolactone and 3,4-Dihydroxybutyric Acid In Escherichia Coli
3-hydroxy-γ-butyrolactone (3-HBL), one of the top ten value added chemicals from biomass in a 2004 Department of Energy report, is a versatile chiral building block, frequently used in the pharmaceutical industry for synthesis of blockbuster drugs like Zetia®, cholesterol reducing synthetic statins such as atorvastatin and rosuvastatin, antibiotics such as carbapenems and linzolid (Zyvox®) and the nutritional supplement L-Carnitine. Our group established the first complete biosynthetic pathway towards 3-HBL and its hydrolyzed form, 3,4-dihydroxybutyric acid (DHBA) in Escherichia coli using glucose and glycolate as feedstocks. Glycolate itself may be synthesized from glucose in E. coli, using the endogenous glyoxylate shunt, eliminating the need to supply it as a separate feedstock. Integration of this endogenous glycolate synthesis pathway with the already established 3-HBL/DHBA pathway has allowed us to successfully demonstrate for the very first time the direct synthesis of 3-HBL and DHBA from glucose as a sole feedstock, opening avenues for synthesis of these valuable chemicals from other biomass derived simple sugars. Enhancing pathway productivity and titers further requires specific host and pathway engineering efforts to reduce the metabolic burden, enhance cofactor availability and to achieve optimal distribution of the supplied glucose between the endogenous glyoxylate shunt for glycolate synthesis and the de novo constructed 3-HBL/DHBA pathway. Work on the design and engineering of this integrated pathway and the ongoing efforts to improve pathway productivity will be presented.