Optimization, purification and characterization of recombinant L-asparaginase II in <i>Escherichia coli</i>

Abstract

We studied optimal L-asparaginase sequence from GenBank accession number X12746 encoding for Lasparaginase from Erwinia chrysanthemi NCPPB1125. The expression level of recombinant Lasparaginase was determined as 78% of the total proteins. The purified L-asparaginase had a molecular mass of 37 kDa with specific activity of 312.8 U/mg. Kinetic parameters, K_m, V_max, K_cat and K_cat/K_m of purified enzyme were found to be 0.5 mM, 500 U/mg, 14.9  10³ s^-1, and 29.9 X 10³ mM^-1s^-1, respectively. Temperature and pH optimum were observed at 45ºC and pH 7.5, respectively. The enzyme exhibited about 20 and 60% retention of activity following 100 min incubation at 55 or 40°C, respectively. The activity of enzyme was inhibited by EDTA, Hg²⁺, Cu²⁺, Ni²⁺, and enhanced by Mg²⁺. Detergents (Tween 20, Tween 80, Triton X-100, and Triton X-114) decreased enzyme activity. DTT and DMSO at appropriate concentrations enhanced enzyme activity. In vitro anti-cancer activity was performed using different tumor cell lines. Concentration of recombinant L-asparaginase at 50 μg/ml inhibited 45.32, 48.22, 53.68, 51.22% with HL-60, P388, P3X63Ag8, SP2/0-Ag14 cell lines.  Recombinant L-asparaginase was expressed successfully in Escherichia coli with high expression level, had a high specific activity and antiproliferative effect on several tumor cell lines.

Key words: Characterization, Erwinia chrysanthemi, L-asparaginase, purification, tumor cell line.