Alpha 2 HS glycoprotein

Function

Alpha2-HS glycoprotein, a glycoprotein present in the serum, is synthesized by hepatocytes. The AHSG molecule consists of two polypeptide chains, which are both cleaved from a proprotein encoded from a single mRNA. It is involved in several functions, such as endocytosis, brain development and the formation of bone tissue. The protein is commonly present in the cortical plate of the immature cerebral cortex and bone marrow hemopoietic matrix, and it has therefore been postulated that it participates in the development of the tissues. However, its exact significance is still obscure.

The choroid plexus is an established extrahepatic expression site. The mature circulating AHSG molecule consists of two polypeptide chains, which are both cleaved from a proprotein encoded from a single mRNA. Multiple post-translational modifications have been reported. Thus AHSG is a secreted partially phosphorylated glycoprotein with complex proeolytic processing that circulates in blood and extracellular fluids. In the test tube AHSG can bind multiple ligands and therefore has been claimed to be involved in several functions, such as endocytosis, brain development and the formation of bone tissue. Most of these functions await confirmation in vivo.

Fetuins like histidine-rich glycoprotein and kininogens are secreted (so-called type 3) cystatins.

Fetuins are carrier proteins like albumin. Fetuin-A forms soluble complexes with calcium and phosphate and thus is a carrier of otherwise insoluble calcium phosphate. Thus fetuin-A is a potent inhibitor of pathological calcification. Mice deficient in fetuin-A show systemic calcification of soft tissues.