[Characterization and expression optimization of a highly thermostable hexokinase in Escherichia coli]

Hexokinase is a crucial diagnostic reagent in blood glucose testing, which has high requirements for the enzyme activity and thermal stability. The hexokinases in China mainly rely on imports and are primarily sourced from yeast, with high costs and poor thermal stability, which limit the development of blood glucose diagnostic reagents. Therefore, there is an urgent need for the efficient expression of highly active and thermally stable hexokinases. In this study, an ATP-dependent hexokinase (glucokinase, Glk) from a thermophilic bacterium Glk was heterologously expressed in Escherichia coli BL21(DE3). Glk exhibited high specificity for glucose, dependence on Mg²⁺, and the highest activity at pH 8.5 and 80 ℃. It retained over 90% activity after storage at 30-37 ℃ for 7 days, demonstrating thermal stability as an alkaline glucose kinase. Subsequently, the factors influencing Glk expression, including culture medium, OD₆₀₀, final concentration of the inducer, induction temperature, and induction duration, were systematically optimized. The optimization increased the Glk expression by 4.71 folds Glk compared with non-optimized conditions. After purification, Glk exhibited a specific activity of (43.05±2.00) U/mg and the purity ≥98%. In conclusion, the developed expression and purification method for the highly thermostable hexokinase provides more possibilities for overcoming the shortcomings in the preparation of blood glucose diagnostic reagents in China.