Protein S100-A8(Mrp8) contains 2 EF-hand domains and belongs to the S-100 family. Mrp8 binds two calcium ions per molecule with an affinity similar to that of the S-100 proteins. S100 proteins are localized in the cytoplasm and/or 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. It may function in the inhibition of casein kinase and as a cytokine. Altered expression of this protein is associated with the disease cystic fibrosis.