Activating the d -Tagatose Production Capacity of Escherichia coli with Structural Insights into C4 Epimerase Specificity

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High Resolution Image Download MS PowerPoint Slide d -Tagatose, a rare low-calorie sweetener, is ideal for beverages due to its high solubility and low viscosity. Current enzymatic production methods from d -galactose or d -galactitol are limited by reaction reversibility, affecting the yield and purity. This study demonstrates that Escherichia coli harbors a thermodynamically favorable pathway for producing d -tagatose from d -glucose via phosphorylation–epimerization–dephosphorylation steps. GatZ and KbaZ, annotated as aldolase chaperones, exhibit C4 epimerization activity, converting d -fructose-6-phosphate to d -tagatose-6-phosphate. Structural analysis reveals active site differences between these enzymes and class II aldolases, indicating functional divergence. By exploiting the strains’ inability to metabolize d -tagatose, carbon starvation was applied to remove sugar byproducts. The engineered strains converted 45 g L –1 d -glucose to d -tagatose, achieving a titer of 7.3 g L –1 and a productivity of 0.1 g L –1 h –1 under test tube conditions. This approach highlights E. coli as a promising host for efficient d -tagatose production.

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