S100 proteins are low molecular weight calcium binding proteins expressed in vertebrates. biology and in the introduction of joint disease. 1. S100 category of protein S100 proteins was first found out by Moore in mind tissue and called S100-proteins since it was soluble in completely saturated ammonium sulfate . Nevertheless, subsequent studies show that this small fraction included two related protein, S100B and S100A . Presently, the category of S100 protein is made up of 21 known people that are characterized by the presence of two EF-hand domains (calcium binding), one at each N-terminus and C- terminus separated by a hinge region. The carboxylCterminal (c-terminus) EF-hand domain is referred to as the conical (higher affinity) calcium binding loop that encompasses 12 amino acids, whereas the low affinity N-terminal loop formed of 14 amino acids is known as the pseudo or S100-specific EFChand domain [3, 4]. In humans, most S100 genes are clustered at chromosomal locus 1q21 except S100B, S100p and S100Z, which are mapped at chromosome 12q22, 4 and 5 [5C8]. Members of the S100 protein family have sequence homology between 22 to 57% with marked variance at the hinge region and C-terminus, which is thought to contribute to the diversity in their biological function . S100 proteins are expressed in various tissues in a cell type-specific manner and with specific sub-cellular localization [9, 10]. In the cell, S100 proteins exist as dimers (homodimers or heterodimers) or multimers [11C13] wherein the monomeric units of S100 proteins are held together by non-covalent bonds [14C16]. The only exception to this rule is S100G, which always exists as a monomer [17, 18]. In addition, multimerization of S100 protein is also promoted by posttranslational modification of monomeric S100 proteins  and by binding of metal ions [11, 12, 20]. S100 proteins bind various divalent metal ions, including calcium (high affinity), zinc, and copper [21C27]. Binding of these ions BIBR 953 enzyme inhibitor to S100 protein also Tmeff2 modulates their function by altering conformational changes. In the calcium-free state, the EF-hand in each monomer is in anti-parallel confirmation. Upon calcium binding, each S100 monomer opens up to accommodate a target; the S100 BIBR 953 enzyme inhibitor dimer can bind target proteins on opposite sides. Although S100 dimers are characterized by the same structural motif, differences in the primary sequence of individual helices, the hinge region, or the C-terminal region, as well as distinctions in the inter-helical sides in calcium-loaded dimers, could be very important to the reputation of focus on specification and protein of functional jobs of individual S100 members. 2. Biological features of S100 protein S100 protein play a significant role in a wide array of natural functions. They have both extracellular and intracellular functions. Their intracellular features consist of modulation of enzyme activity, calcium mineral homeostasis, cell mobility and growth, cell cycle BIBR 953 enzyme inhibitor regulation, cell differentiation and cell survival . Extracellularly, S100 proteins interact with cell surface receptors, BIBR 953 enzyme inhibitor including receptor for advance glycation end products (RAGE) [28C30] and toll-like receptors (TLR) ,  and participate in signal transduction. S100 proteins lack intrinsic enzymatic activity, but they participate in biological function via protein-protein conversation and modulating the activity of their target molecule. Binding of S100B to nuclear Dbf2-related protein kinase (NDR kinase) directly blocks the recruitment of substrate on NDR kinase . A similar mechanism has been proposed for S100A4-mediated regulation of MetAP2 activity . On the other hand, binding of S100A1 to ryanodine receptor, a cellular mediator of calcium-induced calcium release, increases its affinity for ryanodine (its ligand) several fold, resulting in opening of the RyR channel and increased release of calcium from the sarcoplasmic reticulum in skeletal muscle , thus influencing intracellular calcium homeostasis. Furthermore, studies have shown that multiple members of S100 family can interact with a specific target molecule and have differential effects. For example, S100A1, S100B, S100A4, and S100A11 are known to interact directly with cytoskeletal elements including microtubilin, microfilaments, intermediate filaments, actin, myosin, tropomyosin; regulating cytoskeletal dynamics; and playing a role in cell mobility and proliferation [28, 36C38]. Likewise, many S100 proteins, including S100A2, S100A4, and S100B, interact with tumor suppressor 53 (p53) and modulate its activity differentially. Binding of S100A4 and S100B to p53 negatively modulates its activity to cause cell growth arrest and apoptosis [39C41], whereas binding of S100A2 enhances p53’s transcriptional activity . Binding of multiple S100 proteins to a single target protein is not surprising given the significant homology in their primary sequence, and provides the mechanism for the comparable functional role of the two different S100 proteins in various tissues. Alternatively, the differential impacts of S100 protein in the function of an individual target proteins also could describe functional variety within confirmed tissue. Some known people from the S100 proteins family members are released in to the extracellular environment, where they become cytokines and so are involved with cell.