Receptor-like protein tyrosine phosphatases (RPTPs) represent an important pathway for signal transduction via modification of protein tyrosine phosphorylation status. RPTPα is widely expressed and is particularly abundant in brain. Structurally, it is typical of RPTPs in that it has an intracellular region containing two tandem catalytic domains linked to a transmembrane and an extracellular region. However, unlike many RPTPs, the extracellular region of RPTPα is small (123 residues) and lacks any obvious structural motifs, though the protein is known to be heavily glycosylated. Both catalytic domains of RPTPα have intrinsic in vitro activity, but their exact roles in vivo remain uncertain. It has been postulated that due to their transmembrane nature, RPTPs are initiators for a cascade of intracellular signaling events, much like receptor tyrosine kinases.