Vitamin D-binding protein also known as gc-globulin (group-specific component) is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the GC gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

Vitamin D-binding protein belongs to the albumin

Albumin

Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...

 gene family, together with human serum albumin

Human serum albumin

Human serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein...

 and alpha-fetoprotein

Alpha-fetoprotein

Alpha-fetoprotein is a protein that in humans is encoded by the AFP gene....

. It is a multifunctional protein found in plasma, ascitic fluid, cerebrospinal fluid

Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

 and on the surface of many cell types. It binds to vitamin D

Vitamin D

Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....

and its plasma metabolites and transports them to target tissues.

Structure

Human GC is a glycosylated alpha-globulin, ~58 kDa in size. Its 458 amino acids are coded for by 1690 nucleotides on chromosome 4 (4q11–q13). The primary structure contains 28 cysteine residues forming multiple disulfide bonds. GC contains 3 domains. Domain 1 is composed of 10 alpha helices, domain 2 of 9, and domain 3 of 4.

Further reading