It has been shown [1] that several proteins share two sequence motifs. Two of these proteins are enzymes of the inositol phosphate second messenger signalling pathway:

• Vertebrate, plants and microbial myo-inositol monophosphatase (EC 3.1.3.25).
• Vertebrate inositol polyphosphate 1-phosphatase (EC 3.1.3.57).

The function of the other proteins is not yet clear:

• Bacterial protein cysQ. CysQ could help to control the pool of PAPS (3'-phosphoadenoside 5'-phosphosulfate), or be useful in sulfite synthesis.
• Neurospora crassa protein Qa-X. Probably involved in quinate metabolism.
• Emericella nidulans protein qutG. Probably involved in quinate metabolism.
• Yeast protein HAL2/MET22 [2] involved in salt tolerance as well as methionine biosynthesis.
• Yeast hypothetical hypothetical protein YHR046c.
• Caenorhabditis elegans hypothetical protein F13G3.5.

It is suggested [1] that these proteins may act by enhancing the synthesis or degradation of phosphorylated messenger molecules. From the X-ray structure of human inositol monophosphatase [3], it seems that some of the conserved residues are involved in binding a metal ion and/or the phosphate group of the substrate.