Construction of a synthetic metabolic pathway for biosynthesis of 2,4-dihydroxybutyric acid from ethylene glycol.

Ethylene glycol is an attractive two-carbon alcohol substrate for biochemical product synthesis as it can be derived from CO2 or syngas at no sacrifice to human food stocks. Here, we disclose a five-step synthetic metabolic pathway enabling the carbon-conserving biosynthesis of the versatile platform molecule 2,4-dihydroxybutyric acid (DHB) from this compound. The linear pathway chains ethylene glycol dehydrogenase, D-threose aldolase, D-threose dehydrogenase, D-threono-1,4-lactonase, D-threonate dehydratase and 2-oxo-4-hydroxybutyrate reductase enzyme activities in succession. We screen candidate enzymes with D-threose dehydrogenase and D-threonate dehydratase activities on cognate substrates with conserved carbon-centre stereochemistry. Lastly, we show the functionality of the pathway by its expression in an Escherichia coli strain and production of 1 g L-1 and 0.8 g L-1 DHB from, respectively, glycolaldehyde or ethylene glycol.