<p>This is a small family of large proteins (~1300-1500 residues) containing one copy of the metallophosphoesterase domain. With the exception of glutamine replacing one metal-binding histidine, they possess the motifs characteristic of a variety of enzymatically active phosphoesterases [<cite idref="PUB00014394"/>], including acid and alkaline phosphatases, phosphoprotein phosphatases, 5'-nucleotidase, bis(5'-nucleosyl)-tetraphosphatase (symmetrical), sphingomyelin phosphodiesterase, 2',3'-cylic-nucleotide 2'-phosphodiesterase, and the 3',5'-nucleotide phosphodiesterase CpdA.</p> <p>Although the sequences within this family are well-conserved throughout most of their lengths, with the exception of the portion of the protein containing the metallophosphoesterase domain (about one-sixth of the whole), they have little similarity to any other type of characterised protein.</p>