The main biological function of GC is to combine and transport vitamin D and its metabolites. Each GC molecule contains a VD enzyme binding site, and normally only 1% to 2% of the sites participate in VD metabolism. GC participates in the transport of VD and its metabolites between blood and cell membranes, so most of the plasma is free 6C. GC can bind to actin in vivo or in vitro to form a 1:1 complex, which greatly increases the molecular weight and increases the electrophoretic migration string. The isoelectric point of the Gc actin complex is lower than that of free GC. Gc binding to actin facilitates the clearance of actin from tissues.
Vitamin D binding protein (also known as Gc protein), is an alpha globulin, a group of multi-gene super-including protein (ALB), prealbumin (PA), alpha-fetoprotein (AFP). The family, most of which is secreted by the liver parenchymal cells, has a relative molecular mass of about 55,000. It is abundant in serum and has many physiological functions. It not only binds vitamin D and clears actin, but also enhances C5 to neutral particles. The chemotactic activity of inflammatory cells such as cells, and activation of macrophages, regulation of osteoclast activity and transport of fatty acids and endotoxins, may also be involved in viral infection.
[What is the function of vitamin D binding protein?] 1 Structure of vitamin D receptor VDR is a member of the nuclear receptor superfamily such as thyroxine and corticosteroids. VDR has a large similarity in sequence and structure to subfamilies including retinal, thyroid hormone, and peroxisome proliferator-activated receptors. The study confirmed that the human VDR gene is located on chromosome 12, consisting of 11 exons and several introns, about 75 kb in length, and the protein consists of 427 amino acids. From the amino end to the carboxy end, it can be generally divided into six functional regions: A, B, C, D, E, and F.
The AB region is a ligand-independent, tissue-specific transcriptional activation self-regulating functional region AF1. The human VDR AB region consists of approximately 24 amino acid residues. No features were found in this domain. Region C: DNA binding domain DBD, involved in DNA sequence recognition, and is also partially involved in the formation of dimer interfaces. This region is highly conserved and the homology of human, rat and chicken VDR DBD is 98.15%. Zone E: This region is relatively large and functional: participating in binding ligands, thus referred to as the ligand binding domain LBD; forming a dimer with RXR; forming a ligand-dependent transcriptional activation or inhibition functional region AF2. In addition, the E region also has a synergistic effect on DNA recognition.
Zone D and Zone F: The functions of these two zones are unknown. Zone D may be a hinge region that primarily regulates the flexibility of the receptor and may be related to nuclear localization. 2 VDR regulates the calcium-binding protein gene VDR regulates many genes, most of which are genes in bone metabolism. Here we use the calcium-binding protein gene as an example to introduce the regulation of VDR genes. Calcium is second only to oxygen, carbon, hydrogen and nitrogen in the body, accounting for about 2% of the human body. Calcium absorption is a complex physiological and biochemical process, including active transport and passive diffusion. Active transport is the main factor when the body consumes less calcium. Active transport of calcium requires the assistance of vitamin D and calcium binding proteins.
Wasserman et al. first confirmed the formation of specific calcium-binding protein (CaBP) after treatment of rickets with vitamin D. This vitamin D-induced CaBP has been found in more than a dozen animals and is species-specific. The molecular weight of human intestinal calcium CaBP is 12000-21000, which has a high affinity with calcium, and the ability to bind calcium is about 2×10-5M-1. CaBP is highly concentrated on the absorption cells of the goblet cells and the brush border of the small intestine.
In different parts of the intestine, intestinal CaBP level and calcium absorption rate are consistent, with the highest in the duodenum, the second in the jejunum, and the lowest in the ileum. In addition, CaBP is also present in tissues such as the kidney, hypothalamus, cerebral cortex, adrenal gland, and parathyroid glands. CaBP plays an important role in the process of vitamin D-mediated intestinal calcium transport. Mammals can synthesize two CaBPs, namely CaBPD28K present in the kidney and central nervous system and CaBPD9K in the small intestine. Injection of 125OH2D3 into vitamin D-deficient rats and chicks resulted in rapid synthesis of CaBP mRNA and accumulation of CaBPD9K mRNA in intestinal mucosa and kidney cells.
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