Directed Evolution of Glutamate Dehydrogenase for Oxaloacetate Amination and Biosynthesis of Aspartate-Derived Chemicals

l-aspartate and its derivatives are essential not only for protein biosynthesis but also as key branch points for producing high-value chemicals. However, microbial synthesis of l-aspartate is often limited by low catalytic efficiency in the conversion of oxaloacetate to l-aspartate. Here, we engineered NADPH-dependent glutamate dehydrogenase (GDH) from Escherichia coli through structure-guided design coupled with high-throughput screening and obtained a variant that efficiently aminates oxaloacetate. The engineered enzyme shows strong substrate preference for oxaloacetate and achieves a kcat value 3.7-fold higher than that of aspartate aminotransferase (AspC). Introducing this variant into biosynthetic pathways for l-aspartate and β-alanine increased their yields by 3-fold and 2-fold, respectively. Moreover, overexpressing the variant in a threonine-producing strain improved threonine production to a final titer of 29.5 g/L in shake-flask cultivation. This work demonstrates that engineering NADPH-dependent GDH is a promising strategy for efficient biomanufacturing of aspartate-derived chemicals.