Enhancing the thermostability of Escherichia colil-asparaginase II by substitution with pro in predicted hydrogen-bonded turn structures

l-Asparaginase II of E. coli is a kind of effective drug in the treatment of acute lymphoblastic leukaemia. However, during asparaginase therapy, repeated using of the drug is commonly needed because of the enzyme's relatively short half-life and instability in the processes of production and treatment. This leads to more serious toxic effects on patients. In order to stabilize the enzyme, a higher thermostable mutant l-asparaginase II was created in the present study by replacing Asp178 with proline in a hydrogen-bonded turn (178–180DGR) which is contribute to the thermostability of the enzyme. The results displayed that values of Km and Kcat for the mutant enzyme are not affected although the energy of activation is increased comparing to the wild-type enzyme. These data suggest that such alteration for l-asparaginase II enhances the thermostability of the enzyme without changing the enzyme's activity and thus the therapeutical use of l-asparaginase II might be benefit from these results.