The Crystal Structure of<i>N</i>¹⁰-Formyltetrahydrofolate Synthetase from<i>Moorella thermoacetica</i>^,

The structure was solved at 2.5 Å resolution using multiwavelength anomalous dispersion (MAD) scattering by Se-Met residues. The subunit of N10-formyltetrahydrofolate synthetase is composed of three domains organized around three mixed β-sheets. There are two cavities between adjacent domains. One of them was identified as the nucleotide binding site by homology modeling. The large domain contains a seven-stranded β-sheet surrounded by helices on both sides. The second domain contains a five-stranded β-sheet with two α-helices packed on one side while the other two are a wall of the active site cavity. The third domain contains a four-stranded β-sheet forming a half-barrel. The concave side is covered by two helices while the convex side is another wall of the large cavity. Arg 97 is likely involved in formyl phosphate binding. The tetrameric molecule is relatively flat with the shape of the letter X, and the active sites are located at the end of the subunits far from the subunit interface.