S S 100 Calcium - Binding Protein ▶ S 100 Proteins S 100 Proteins

S100 proteins were first discovered in 1965 by Moore as a major protein fraction (0.6% of total soluble protein) isolated from bovine brain (Moore 1965). The protein was given the name S100 due to its high solubility in saturated ammonium sulfate. Later experiments showed the S100 protein fraction constituted two different dimeric species comprised of two b protomers (S100B) or an a, b heterodimer (Isobe et al. 1977). Early members of the S100 protein family were frequently given suffixes based on their localization or molecular size and included S100P (placental), S100C (cardiac or calgizzarin), p11 (11 kDa), and MRP8/MRP14 (myeloid regulatory proteins, 8 and 14 kDa). In 1993, initial genetic studies showed that six of the S100 genes were clustered on chromosome 1q21 (Engelkamp et al. 1993), a number that has expanded since. Based on this observation most of the proteins were renamed according to the physical order they occupy on the chromosome. These include S100A1 (formerly S100a), S100A2 (formerly S100L), S100A10 (p11), S100A8/S100A14 (MRP8/MRP14). A few S100 proteins are found on other chromosomes including S100B (21q21). Currently there are 27 known S100 family members: S100A1-A18, S100B, S100G, S100P, S100Z, trichohylin, filaggrin, filaggrin2, cornulin, and repetin (Table 1).