A family of vertebrate small membrane proteins is collectively known as FXYD in recognition of invariant amino acids in its signature motif. These proteins are involved in the control of ion transport and consist of the following members [1,2]:

• Phospholemman (gene FXYD1).
• Sodium/potassium-transporting ATPase γ chain (gene FXYD2).
• Chloride conductance inducer protein mat-8 (gene FXYD3).
• Channel inducing factor (CHIF) (gene FXYD4).
• FXYD5 (RIC; OIT2).
• FXYD6
• FXYD7
• FXYD8

Except for FXYD5, all these proteins are very small and their size range from 58 residues for FXYD2 to 95 for FXYD6. FXYD5 is longer (178 residues) due to a N-terminal extension. They all contain a single transmembrane domain. With the exception of FXYD2, they all seem to have a N-terminal signal peptide. As a signature pattern, we selected a conserved region that start a few residues before the beginning of the transmembrane domain and that stop four residues inside that region.