STYX belongs to the protein-tyrosine phosphatase family, Non-receptor class subfamily. It contains one tyrosine-protein phosphatase domain and is a probable pseudophosphatase. It has a Gly residue instead of a conserved Cys residue in the dsPTPase catalytic loop which renders it catalytically inactive as a phosphatase. The binding pocket is however sufficiently preserved to bind phosphorylated substrates, and may be protect them from phosphatases. STYX seems to play a role in spermiogenesis.