Tyrosine-protein kinase, receptor Tie-2, Ig-like domain 1, N-terminal (Tyr_kin_Tie2_Ig-like_dom-1_N)
Type: Domain

This entry represents the N-terminal domain of human Angiopoietin-1 receptor, also known as Tyrosine-protein kinase receptor TIE-2, and similar sequences from vertebrates.

Angiogenesis is a physiological process whereby new blood vessels are formed from existing ones. It is essential for tissue repair and regeneration during wound healing but also plays important roles in many pathological processes including tumor growth and metastasis . Angiogenesis is regulated in part by the receptor protein tyrosine kinase Tie2 and its ligands, the angiopoietins. The angiopoietin-binding site is harbord by the N-terminal two immunoglobulin-like (Ig-like) domains of Tie2 .

The angiopoietin-1 receptor contains the Tie-2 Ig-like domain. This protein is a tyrosine-kinase transmembrane receptor for angiopoietin 1. It probably regulates endothelial cell proliferation, differentiation and guides the proper patterning of endothelial cells during blood vessel formation.

Tie2 contains not two but three immunoglobulin domains. They fold together with the three epidermal growth factor domains to form a compact, arrowhead-shaped structure .

Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process.
Protein kinases fall into three broad classes, characterised with respect to substrate specificity :

Serine/threonine-protein kinases

Tyrosine-protein kinases

Dual specificity protein kinases (e.g. MEK -phosphorylates both Thr and Tyr on target proteins)

Protein kinase function is evolutionarily conserved from Escherichia coli to human . Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation . Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved , leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases .

Tyrosine-protein kinases can transfer a phosphate group from ATP to a tyrosine residue in a protein. These enzymes can be divided into two main groups :

Receptor tyrosine kinases (RTK), which are transmembrane proteins involved in signal transduction; they play key roles in growth, differentiation, metabolism, adhesion, motility, death and oncogenesis . RTKs are composed of 3 domains: an extracellular domain (binds ligand), a transmembrane (TM) domain, and an intracellular catalytic domain (phosphorylates substrate). The TM domain plays an important role in the dimerisation process necessary for signal transduction .

Cytoplasmic/non-receptor tyrosine kinases, which act as regulatory proteins, playing key roles in cell differentiation, motility, proliferation, and survival. For example, the Src-family of protein-tyrosine kinases .