Abstract
The HD domain motif is found in a superfamily of proteins in bacteria, archaea and eukaryotes. A few of these proteins are known to have metal-dependant phosphohy-drolase activity, but the others are functionally unknown. Here we have character-ized an HD domain-containing protein, TT1383, from Thermus thermophilus HB 8. This protein has sequence similarity to Escherichia coli dGTP triphosphohydrolase, however, no dGTP hydrolytic activity was detected. The hydrolytic activity of the protein was determined in the presence of more than two kinds of deoxyribonucleo-side triphosphates (dNTPs), which were hydrolyzed to their respective deoxyribonu-cleosides and triphosphates, and was found to be strictly specific for dNTPs in the fol-lowing order of relative activity: dCTP>dGTP>dTTP>dATP. Interestingly, this dNTP triphosphohydrolase (dNTPase) activity requires the presence of dATP or dTTP in the dNTP mixture. dADP, dTDP, dAMP, and dTMP, which themselves were not hydrolyzed, were nonetheless able to stimulate the hydrolysis of dCTP. These results suggest the existence of binding sites specific for dATP and dTTP as positive modulators, distinct from the dNTPase catalytic site. This is, to our knowledge, the first report of a non-specific dNTPase that is activated by dNTP itself.
