S100B
Description
The S100B (S100 calcium binding protein B) is a protein-coding gene located on chromosome 21.
S100 calcium-binding protein B (S100B) is a protein of the S100 protein family. S100 proteins are localized in the cytoplasm and nucleus of a wide range of cells, and involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. S100 genes include at least 13 members which are located as a cluster on chromosome 1q21; however, this gene is located at 21q22.3.
== Function == S100B is glial-specific and is expressed primarily by astrocytes, but not all astrocytes express S100B. It has been shown that S100B is only expressed by a subtype of mature astrocytes that ensheath blood vessels and by NG2-expressing cells. This protein may function in neurite extension, proliferation of melanoma cells, stimulation of Ca2+ fluxes, inhibition of PKC-mediated phosphorylation, astrocytosis and axonal proliferation, and inhibition of microtubule assembly. In the developing CNS it acts as a neurotrophic factor and neuronal survival protein. In the adult organism it is usually elevated due to nervous system damage, which makes it a potential clinical marker.
== Clinical significance == Chromosomal rearrangements and altered expression of this gene have been implicated in several neurological, neoplastic, and other types of diseases, including Alzheimer disease, Down syndrome, epilepsy, amyotrophic lateral sclerosis, schwannoma, melanoma, and type I diabetes mellitus. It has been suggested that the regulation of S100B by melittin has potential for the treatment of epilepsy.
== Diagnostic use == S100B is secreted by astrocytes or can spill from injured cells and enter the extracellular space or bloodstream.
S100B is a small protein that binds both zinc and calcium. It is highly concentrated in astrocytes, making it one of the most abundant soluble proteins in the brain. While S100B weakly binds calcium, it exhibits a strong affinity for zinc. Each monomer possesses distinct binding sites with varying affinities for these ions. Physiological concentrations of potassium ions can interfere with the binding of both divalent cations, particularly affecting high-affinity calcium-binding sites. S100B functions as a neurotrophic factor, promoting astrocytosis and axonal proliferation. It also plays a role in the innervation of thermogenic adipose tissue, acting as an adipocyte-derived neurotrophic factor that stimulates sympathetic innervation of adipose tissue. S100B binds to and activates STK38 by disrupting autoinhibitory intramolecular interactions within the kinase. Following myocardial infarction, interactions between S100B and AGER may contribute to myocyte apoptosis by activating ERK1/2 and p53/TP53 signaling. S100B might facilitate the cytoplasmic processing of ATAD3A, preventing aggregation and promoting mitochondrial localization. S100B may regulate numerous physiological processes in a calcium-dependent manner by interacting with other proteins, such as those containing TPR domains, and modulating their activity.
S100B is also known as NEF, S100, S100-B, S100beta.
