Functional expression of the dihydrofolate reductase domain of Leishmania major dihydrofolate reductase-thymidylate synthase bifunctional protein.

The dihydrofolate reductase (DHFR) domain of the bifunctional dihydrofolate reductase-thymidylate synthase from Leishmania major has been subcloned and expressed as a soluble protein in Escherichia coli strain PA414 harboring plasmid pLMDHFR. Homogeneous L. major DHFR was obtained by chromatography on methotrexate-Sepharose followed by DE52. The purified enzyme migrated as a single 25-kDa protein on SDS-PAGE. The native molecular weight was determined to be 26 kDa, indicating that the isolated domain is a monomer. N-terminal sequence analysis revealed that serine, the second amino acid in the coding sequence, was the N-terminal amino acid of the protein. The enzyme showed a pH optimum similar to that of the bifunctional protein. For purified DHFR, the Km values were <1.0 microM for H2folate and <1.0 microM for NADPH. The kcat of the most active DHFR preparation was 5 s-1. The Km and kcat values were similar to those of the bifunctional enzyme.