Specificity
The S-100 proteins are small calcium-binding proteins which display different expression patterns in human tissues. Some S-100 proteins are associated with tumor development and the metastatic behavior of tumors. S-100A5 (S100 calcium binding protein A5) is a 92 amino acid protein that belongs to the S-100 family. Containing two EF-hand domains, S-100A5 binds calcium, zinc and copper. One subunit can simultaneously bind two calcium ions or two copper ions plus one zinc ion. Calcium and copper ions compete for the same binding sites on the S-100A5 protein. The S-100A5 protein is expressed in very restricted regions of the adult brain. The S-100A5 gene is conserved in chimpanzee, dog, cow, mouse and rat, and maps to human chromosome 1q21.3. S100 genes include at least 13 members which are located as a cluster on chromosome 1q21. Due to the clustered organization of the S-100 proteins a new logical nomenclature based on their physical arrangement on the chromosome has been described, with S-100A1 being closest to the telomere and S-100A9 being closest to the centromere.
