The HD domain defines a new superfamily of metal-dependent phosphohydrolases

A hitherto-undescribed (HD) superfamily of predicted phosphohydrolases was characterized. This superfamily of enzymes was related to metalloenzymes, specifically the eukaryotic cyclic-nucleotide phosphodiesterases. These enzymes were predicted to be capable of phosphohydrolase activities and were involved in signal transduction and nucleic acid metabolism. Three motifs were identified in the enzymes: I, II and V. Motif I and V possessed histidine and aspartate residues, respectively, while motif II contained the HD signature.