Molecular characterization, heterologous expression and kinetic analysis of recombinant Plasmodium falciparum thymidylate kinase

The gene encoding for thymidylate kinase from Plasmodium falciparum was obtained by PCR and expressed in Escherichia coli and the enzyme was investigated as a possible new drug target. The enzyme is a homodimer exhibiting maximal kinase activity over a wide pH range of 7-9 and is characterized by marked stability. Compared with the human enzyme, the recombinant P. falciparum TMP kinase showed a broader spectrum of substrate specificity. The enzyme not only phosphorylates dTMP and dUMP but can also tolerate the bulkier purines dGMP, GMP and dIMP. Initial velocity studies showed that the Km values for TMP and dGMP are 22 and 30 microM, respectively. The turnover number kcat(TMP) was found to be 3.4 s(-1), a value indicating the higher catalytic efficiency of the plasmodium enzyme. From the present study, we suggest that the design of appropriate inhibitors especially purine based compounds could have a selective inhibitory effect on the parasite enzyme.