Crystal Structure of FolD Bifunctional Protein, a Methylenetetrahydrofolate Dehydrogenase/Cyclohydrolase from Campylobacter jejuni

Abstract

Tetrahydrofolate (THF) plays a crucial role as a molecule for the production and utilization of monocarbon units in various oxidation states. Enzymes involved in THF metabolism are of pharmaceutical interest, as their function is crucial for amino acid and DNA synthesis. The interconversion of two major one‐carbon donors, methylene and methenyl groups, occurs through the sequential activities of NAD(P)‐dependent methylenetetrahydrofolate dehydrogenase (MTHFD) and methenyltetrahydrofolate cyclohydrolase (MTHFC). These activities frequently coexist as a part of a bifunctional enzyme in prokaryotes. In higher organisms, MTHFR and MTHFC are often linked together with another protein, formyl‐THF synthetase (FTHFS) and operate as a trifunctional enzyme. We have determined the crystal structure of a FolD protein, a predicted MTHFR/MTHFC from Campylobacter jejuni at 2.20 Å resolution. The protein exists as a dimer and each subunit is composed of two α/β domains that assemble to form a wide, largely hydrophobic cleft. Comparison with the structure of the homologous enzyme domain from a trifunctional human protein allowed the identification of a highly conserved cluster of basic residues that most likely participate in the binding of a THF substrate. Exploring the differences between the active sites of bacterial and human enzymes might allow the development of inhibitors specific to the bacterial target. This research was supported by the NIH contract No. HHSN272200700058C, and by the U.S. DOE, Office of Biological and Environmental Research, contract DE‐AC02‐06CH11357.