Structural domains comprising this superfamily share the structure of the 14 kDa phosphohistidine phosphatase from mammals (PHPT1) and Janus-A/Janus-B proteins from Drosophila melanogaster. The PHPT1 DNA sequence shows similarity to testes-specific proteins in Drosophila, ocnus, Janus-A, and Janus-B. These proteins may be phosphatases, but there is little available information on their function. The 14 kDa phosphohistidine phosphatase is of a novel topology, and the structure reveals a positively charged active site defined by conserved residues that provide a suitable environment for binding phosphohistidine-containing substrates PMID:16990267. It is thought that this protein may play a role of reversible histidine phosphorylation in neuronal functions PMID:12468887.