(596a) Novel Pathway Design for the Microbial Production of Biopolymer Building Blocks

Polyhydroxyalkanoates (PHAs) are renewably-derived, microbial polyesters composed of hydroxy acids (HAs). Demand for sustainable plastic alternatives, combined with the unfavorable thermal properties exhibited by some PHAs, motivates the discovery of novel ones. HA structure can be tuned to realize a breadth of material properties useful for industrial application. This diversity remains untapped since the reverse β-oxidation (rBOX) pathway – the canonical metabolic pathway for PHA production – utilizes thiolases with narrow substrate specificity. Here, we present a thiolase-independent pathway to α-substituted 3-hydroxy acids (α-3HAs). PHAs composed of α-3HAs are known to exhibit improved thermal properties and until recently, these HAs were inaccessible via rBOX pathways. Inspired by natural routes of branched chain amino acid catabolism, this pathway involves the conversion of glucose to various branched acyl-CoAs, dehydrogenation of the acyl-CoA to an enoyl-CoA, stereospecific hydration to a 3-hydroxyacyl-CoA, and hydrolysis of this product to an α-3HA. As proof of concept, we engineered Escherichia coli for the specific conversion of glucose to isobutyrate or 2-methylbutyrate and ultimately to 3-hydroxyisobutyric acid and 3-hydroxy-2-methylbutyric acid, respectively. This work illustrates the utility of co-opting branched chain amino acid catabolism for the production of novel HAs leading to PHAs with industrially relevant properties.