Subcellular distribution of serine hydroxymethyltransferase in Plasmodium lophurae

A three-dimensional structure of Plasmodium falciparum serine hydroxymethyltransferase in complex with glycine and 5-formyl-tetrahydrofolate. Homology modeling and molecular dynamics

Cytosolic Plasmodium falciparum serine hydroxymethyltransferase (pfSHMT) is a potential target for antimalarial chemotherapy. Contrasting with the other enzymes involved in the parasite folate cycle, little information is available about this enzyme, and its crystallographic structure is unknown yet. In this paper, we propose a theoretical low-resolution 3D model for pfSHMT in complex with glycine and 5-formyl tetrahydrofolate (5-FTHF) based on homology modeling by multiple alignment followed by intensive optimization, validation and dynamics simulations in water. Comparison between the active sites of our model and that of crystallographic Human SHMT (hSHMT) revealed key differences that could be useful for the design of new selective inhibitors of pfSHMT.

Gene organization of a Plasmodium falciparum serine hydroxymethyltransferase and its functional expression in Escherichia coli

The global emergence of drug-resistant malarial parasites necessitates identification and characterization of novel drug targets. Three reactions are involved in methylenetetrahydrofolate recycling: Thymidylate synthase (TS), dihydrofolate reductase (DHFR), and serine hydroxymethyltransferase (SHMT). Malarial bifunctional DHFR-TS is a well-studied, important target of established drugs such as pyrimethamine and cycloguanil. In sharp contrast, malarial SHMT remains largely uncharacterized. In the present study, a Plasmodium falciparum SHMT coding region was characterized. It had 1603 bp including two introns near the 5'-end of the gene: one 118 bp intron immediately after the start methionine and a 159 bp intron after an additional 34 amino acids. The three exons together coded for a 442 amino acid protein with 38-47% identity to SHMT sequences from other species. Expression of malarial SHMT coding sequence (minus the introns) into glyA mutants of Escherichia coli relieved glycine auxotrophy and permitted direct assay of SHMT catalytic activity in bacterial cell lysates. This is the first SHMT cloned and expressed from a protozoan parasite. The molecular tools developed in this study will be useful for developing potential antimalarials directed at SHMT.