PURIFICATION AND CHARACTERIZATION OF THE NATIVE AND THE RECOMBINANT LEISHMANIA MEXICANA GLYCOSOMAL GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE

The gene coding for the glycosomal glyceraldehyde-3-phosphate dehydrogenase from Leishmania mexicana has been cloned into vector pET3A and expressed as a soluble and active protein in Escherichia coli BL21(DE3) in which the endogenous gene has been inactivated by mutation. The recombinant enzyme was purified to near homogeneity by ammonium sulphate precipitation, followed by hydrophobic and cation-exchange chromatography. From a 1-L culture of E. coli cells, 25 mg purified protein was obtained with a specific activity of 125 units/mg. The recombinant protein restores the natural E. coli phenotype when expressed at low level. The enzyme has also been partially purified from glycosomes of cultured L. mexicana promastigotes. The recombinant and the native proteins show identical mobilities on SDS/PAGE, and have the same isoelectric point and similar pH-activity profiles. The kinetics of both enzymes are very similar, the most important aspect being their lower apparent affinity for the cofactor NAD when compared to all other homologous enzymes studied, with the exception of glycosomal glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma brucei.