Description
Vitamin D binding protein (VDBP, also known as group-specific component / Gc protein) is a multifunctional serum protein which is formed in the liver.
VDBP can be found in plasma, ascites, liquor, urine and at the surface of various cell types. High estrogen levels caused by pregnancy or hormonal birth control, for example, stimulate its synthesis. In the blood, VDBP binds the bigger part of the circulating 25-OH vitamin D and brings it to the kidneys, where it is transformed into the hormone 1,25-(OH)2 vitamin D. In addition, VDBP binds monomeric actin at the ratio of 1:1. Actin is an intracellular protein which is available as monomer or filament. Massive tissue destruction or cell death cause the plasma level of actin to rise significantly, whereupon VDBP-actin complexes are formed which are removed quickly. Hence the VDBP level of trauma or sepsis patients decreases quickly, especially in patients with a high level of multiorgan failure. Furthermore VDBP is a precursor of the immunomodulating protein Gc-MAF (Gc protein-derived macrophage activating factor) which increases the activity of macrophages against tumours.
