STYX is a member of the protein-tyrosine phosphatase family. STYX has a Gly residue instead of a conserved Cys residue in the dsPTPase catalytic loop which renders it catalytically inactive as a phosphatase. Nevertheless, the binding pocket is adequately preserved to bind phosphorylated substrates, and possibly protect them from phosphatases. STYX takes part in spermiogenesis.