Current progress in structure and function of angiopoietin family

Angiopoietin family is a recently discovered type of cellular factors that specifically bind to the TIE-2 receptors located exclusively in endothelial cell membrane. The protein structures of this family members are similar. They can be structurally divided into three domains: an N-terminal region lacking homology to any known structures, an alpha-helical rich coiled-coil segment, and a fibrinogen-like domain. The distribution and biological activity of these factors are different in organism. Angiopoietin-1 as a agonist, mostly locates in close proximity with vascular endothelial cells, keeps the stability of blood vessels, enhances the affinity of vascular endothelial cells with surrounding cells and matrix, decreases the leakage of vessel. Ang-2 is a naturally occurring antagonist of Ang-1, exists in the angiogenic remodeling region and is related to the decrement of the stability of vessel. Ang-3 is widely distributed in multiple mouse tissues, while Ang-4 is expressed only in lung. Although Ang-3 and Ang-4 are structurally diverged from each other, they appear to represent the mouse and human counterparts of the same gene locus. Biological functions of Ang-3 and Ang-4 have not been elucidated yet. Angiopoietin family has potentially clinical applications for incurring illnesses which lead to vessel wound and vascular abnormal development.