GC

GC Full Name

group-specific component (vitamin D binding protein)

GC Introduction

Group-specific component (GC), more commonly known as Vitamin D-binding protein (DBP), is a critical multifunctional glycoprotein in human plasma. It is encoded by the GC gene located on the long arm of human chromosome 4 (4q11–q13), primarily synthesized and secreted into the blood by the liver, and belongs to the α2-globulin family. In the circulatory system, GC protein is present at relatively high concentrations, making it the principal carrier protein for vitamin D and its metabolites. Over 95% of 25(OH)D and more than 85% of 1,25(OH)₂D in plasma are bound to GC protein. This strong binding not only significantly extends the half-life of vitamin D metabolites and prevents their rapid renal clearance, but also forms a large circulating reservoir, ensuring a stable supply of vitamin D to target tissues when needed. A notable feature of GC protein is its high degree of genetic polymorphism, mainly determined by three co-dominant alleles (Gc1F, Gc1S, and Gc2), which together give rise to six common phenotypes. These different genotypes lead to variations in the structure and binding affinity of GC protein, as well as its concentration levels across different populations.

Figure 1. Physiological roles of vitamin D-binding protein (encoded by the group-specific component, GC gene), 1-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), and vitamin D receptor (VDR) genes in vitamin D mechanism. (Source: Wu X, et al. 2016)

GC protein plays a key scavenger role in the body's response to tissue injury and cell death. When cells undergo necrosis or apoptosis, they release large amounts of globular actin (G-actin), which can spontaneously polymerize into filamentous actin (F-actin) in circulation, potentially leading to microvascular occlusion and multiple organ failure. GC protein is the most potent known plasma actin scavenging system; it binds to G-actin monomers to form stable complexes, prevents their polymerization, and facilitates transport of the complexes to the liver for clearance. This function provides crucial protection in severe conditions such as trauma and sepsis.

Secondly, GC protein serves as a precursor for powerful immunoregulatory molecules. Through modification by glycosidases on the surface of B cells and T cells, GC protein can be converted into a molecule known as "macrophage-activating factor" (Gc-MAF), which greatly enhances the phagocytic ability and anti-tumor activity of macrophages, serving as an important bridge between innate and adaptive immunity. Furthermore, GC protein is involved in other biological processes, such as binding endotoxins, modulating inflammatory responses, and transporting fatty acids.

Alternate Names for GC

GC; group-specific component (vitamin D binding protein); DBP; GRD3; VDBG; VDBP; DBP/GC; HEL-S-51; vitamin D-binding protein; VDB; gc-globulin; vitamin D-binding alpha-globulin; epididymis secretory protein Li 51;

• 1. Wu X, et al. Vitamin D-Related Gene Polymorphisms, Plasma 25-Hydroxy-Vitamin D, Cigarette Smoke and Non-Small Cell Lung Cancer (NSCLC) Risk. Int J Mol Sci. 2016 Sep 22;17(10):1597.
  2. Bouillon R, et al. Vitamin D Binding Protein: A Historic Overview. Front Endocrinol (Lausanne). 2020 Jan 10;10:910.