Protein tyrosine phosphatases (PTP) catalyze the removal of phosphate from tyrosine residues of protein substrates. Most PTPs use a cysteine-based catalytic mechanism and are defined by the active-site signature motif Cys-X5-Arg - they include classical PTPs (either transmembrane receptor or cytosolic) and dual specificity PTPs. The EYA class of PTPs define a small additional group that display an aspartic acid-based catalytic mechanism. (Adapted from FBrf0129980 and PMID:17057753.)