The Refined Structure of dUTPase from Escherichia coli

Deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase, E.C. 3.6.1.23) catalyzes the hydrolysis of dUTP to dUMP and pyrophosphate and is involved in nucleotide metabolism and DNA synthesis. A crystal of the recombinant E. coli enzyme, precipitated from polyethylene glycol mixtures in the presence of succinate at pH 4.2, was used to collect synchrotron diffraction data to 1.9 Å resolution, in space group R3, a = b = 86.62, c = 62.23 Å. Mercury and platinum derivative data were collected at wavelengths to optimize the anomalous contribution. The resulting 2.2 Å MIRAS phases differed from the final set by 40° on average and produced an excellent map which was easy to interpret. The model contains 132 water molecules and refined to an R value of 13.7%. 136 residues have clear electron density out of 152 expected from the gene sequence. The 16 C-terminal residues are presumably disordered in the crystal lattice. The monomer is a `jelly-roll' type, containing mostly -sheet and only one short helix. The molecule is a tight trimer. A long C-terminal arm extends from one subunit and encompasses the next one within the trimer contributing to its -sheet. Conserved sequence motifs common among dUTPases, previously suggested to compose the active site and confirmed in a recent study of the dUDP complex, are located at subunit-subunit interfaces along the threefold axis, in parts of the -sheet and in loop regions. A similar molecular architecture has recently been found in two other trimeric dUTPases.