Tie-1/Tie and Tie-2/Tek are receptor tyrosine kinases with unique structural characteristics including two immunoglobulin-like domains flanking three epidermal growth factor (EGF)-like domains, followed by three fibronectin type III-like repeats in the extracellular region, and a split tyrosine kinase domain in the cytoplasmic region. Tie-2 is a receptor for the angiopoietin (ANG) family: Ang-1, Ang-2, and Ang-3 (mouse)/-4 (human). It is involved in vascular stabilization and remodeling. Although less well understood, Tie-1 may also act as an ANG receptor, possibly in complex with Tie-2.