Biosynthesis of 3-Hydroxyalkanoic Acids and Lactones in Escherichia Coli

Hydroxyacids and lactones are versatile, chiral compounds that can readily be modified into several useful derivatives. Specifically, these compounds see use in the synthesis of antibiotics, beta- and gamma-aminoacids and peptides, in fragrances, and as chiral synthetic building blocks. These compounds can also be used directly as nutritional supplements and can be polymerized into biodegradable polyesters with interesting physical properties.

In this work, we report on the chiral biosynthesis of a broad range of 3-hydroxyalkanoic acids including 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 3,4-dihydroxybutyrate, and 3-hydroxybutyrolactone. Metabolic pathways were developed for these products by exploring the substrate promiscuity of several enzymes from polyhydroxyalkanoate biosynthesis, and special attention was paid to controlling the stereochemistry of the final product through the choice of enzymes employed in each pathway. Many of the above compounds have never been synthesized biologically before, including 3-hydroxybutyrolactone, which is listed in a 2004 report from the Department of Energy as one of the top ten value added chemicals from biomass and is used in the pharmaceutical industry as the central building block for statin-class drugs. All of the above 3-hydroxyalkanoic acids were produced on coenzyme A (CoA) carriers, and developing metabolic strategies for the effective thiolation and hydrolysis of these hydroxyacids and their CoA derivatives was critical in enabling many of the biosynthetic pathways in this work.