High Yield Fermentation of L-serine in Recombinant Escherichia coli via Co-localization of SerB and EamA through Protein Scaffold

L-serine is a non-essential amino acid which has a wide range of applications and plays an important role as a building block for growing cells. L-serine microbial development is considered a difficult activity due to L-serine’s central role in cellular metabolism with 2 main degradation pathways. A novel strategy is needed to overcome the L-serine degradation pathway and low L-serine tolerance of Escherichia coli for efficient L-serine production. A synthetic protein scaffold between SerB and EamA was introduced in this study to physically combine the two enzymes. Through this strategy, the L-serine production is more efficient than in competing pathways. By the introduction of a synthetic protein scaffold without metabolic pathway engineering or addition of glycine, 1.8 g/L of L-serine was produced at pH7 and 37°C. By fermentation, 9.4 g/L of serine was produced at a yield of 0.34 mol/mol glucose. These results suggest that the carbon flux was successfully directed to the L-serine secretion pathway without knocking out a competing pathway or adding expensive glycine.