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.

Human Tie-1 cDNA encodes a 1138 amino acid (aa) residue precursor protein with a 24 residue putative signal peptide, a 735 residue extracellular domain and a 354 residue cytoplasmic domain. Ligands which bind and activate Tie-1 have not been identified. Based on gene targeting studies, the in vivo functions of Tie-1 have been shown to be related to endothelial cell differentiation and the maintenance of integrity of the endothelium.