S100 calcium-binding protein A5 (S100A5) is a protein that is encoded by the S100A5 gene in humans.
The protein encoded by this gene is a member of the S100 family of proteins containing 2 EF-hand calcium-binding motifs. S100 proteins are localized in the cytoplasm and/or nucleus of a wide range of cells and are 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. This protein has a Ca<sup>2+</sup> affinity 20- to 100-fold higher than the other S100 proteins studied under identical conditions. This protein also binds Zn<sup>2+</sup> and Cu<sup>2+</sup>, and Cu<sup>2+</sup> strongly which impairs the binding of Ca<sup>2+</sup>. This protein is expressed in very restricted regions of the adult brain.