Chemistry:Vitamin D-binding protein

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Short description: Mammalian protein found in Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Vitamin D-binding protein (DBP), also/originally known as gc-globulin (group-specific component), is a protein that in humans is encoded by the GC gene.[1][2] DBP is genetically the oldest member of the albuminoid family and appeared early in the evolution of vertebrates.[3]

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.[4]

Function

Vitamin D-binding protein belongs to the albumin gene family, together with human serum albumin and alpha-fetoprotein. It is a multifunctional protein found in plasma, ascitic fluid, cerebrospinal fluid and on the surface of many cell types.

It is able to bind the various forms of vitamin D including ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3), the 25-hydroxylated forms (calcifediol), and the active hormonal product, 1,25-dihydroxyvitamin D (calcitriol). The major proportion of vitamin D in blood is bound to this protein. It transports vitamin D metabolites between skin, liver and kidney, and then on to the various target tissues.[2][5]

As Gc protein-derived macrophage activating factor it is a Macrophage Activating Factor (MAF) that has been tested for use as a cancer treatment that would activate macrophages against cancer cells.[6]

Interactive pathway map

Production

It is synthesized by hepatic parenchymal cells and secreted into the blood circulation.[5]

Regulation

The transcription factors HFN1α is a positive regulator while HFN1β is a dominant negative regulator of DBP expression.[7]

Variation

Many genetic variants of the GC gene are known. They produce 6 main haplotypes and 3 main protein variants (Gc1S, Gc1F and Gc2).[8] The genetic variations are associated with differences in circulating 25-hydroxyvitamin D levels.[9] They have been proposed to account for some of the differences in vitamin D status in different ethnic groups,[10] and have been found to correlate with the response to vitamin D supplementation.[8]

References

  1. "Possible localization of Gc-System on chromosome 4. Loss of long arm 4 material associated with father-child incompatibility within the Gc-System". Human Heredity 27 (2): 105–7. Jul 1977. doi:10.1159/000152857. PMID 558959. 
  2. 2.0 2.1 "Entrez Gene: GC group-specific component (vitamin D binding protein)". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=2638. 
  3. Bouillon, R.; Schuit, F.; Antonio, L.; Rastinejad, F. (2020). "Vitamin D Binding Protein: A Historic Overview". Frontiers in Endocrinology 10: 910. doi:10.3389/fendo.2019.00910. PMID 31998239. 
  4. "A structural basis for the unique binding features of the human vitamin D-binding protein". Nature Structural Biology 9 (2): 131–6. February 2002. doi:10.1038/nsb754. PMID 11799400. 
  5. 5.0 5.1 "From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health". The American Journal of Clinical Nutrition 88 (2): 491S–499S. August 2008. doi:10.1093/ajcn/88.2.491S. PMID 18689389. 
  6. "Immunotherapy for Prostate Cancer with Gc Protein-Derived Macrophage-Activating Factor, GcMAF" ([PDF]). Translational Oncology 1 (2): 65–72. July 2008. doi:10.1593/tlo.08106. PMID 18633461. PMC 2510818. http://www.transonc.com/pdf/manuscript/v01i02/neo08106.pdf. 
  7. "Vitamin D Binding Protein: A Historic Overview". Frontiers in Endocrinology 10: 910. 2019. doi:10.3389/fendo.2019.00910. PMID 31998239. 
  8. 8.0 8.1 "Common variants of the vitamin D binding protein gene and adverse health outcomes". Critical Reviews in Clinical Laboratory Sciences 50 (1): 1–22. January–February 2013. doi:10.3109/10408363.2012.750262. PMID 23427793. 
  9. "A systematic review of the association between common single nucleotide polymorphisms and 25-hydroxyvitamin D concentrations". The Journal of Steroid Biochemistry and Molecular Biology 121 (1–2): 471–7. July 2010. doi:10.1016/j.jsbmb.2010.03.073. PMID 20363324. 
  10. "Vitamin D-binding protein and vitamin D status of black Americans and white Americans". The New England Journal of Medicine 369 (21): 1991–2000. November 2013. doi:10.1056/NEJMoa1306357. PMID 24256378. 

Further reading

External links

  • Overview of all the structural information available in the PDB for UniProt: P02774 (Vitamin D-binding protein) at the PDBe-KB.