The crystal structure of N-10-formyltetrahydrofolate synthetase from Moorella thermoacetica

The structure was solved at 2.5 Angstrom resolution using multiwavelength a nomalous dispersion (MAD) scattering by Se-Met residues. The subunit of N-1 0-formyltetrahydrofolate synthetase is composed of three domains organized around three mixed beta-sheets. There are two cavities between adjacent dom ains. One of them was identified as the nucleotide binding site by homology modeling. The large domain contains a seven-stranded beta-sheet surrounded by helices on both sides. The second domain contains a five-stranded beta- sheet with two alpha-helices packed on one side while the other two are a w all of the active site cavity, The third domain contains a four-stranded be ta-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 relativel y 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.