S100A13 is a widely expressed member of the S100 (soluble in 100% saturated ammonium sulfate) family of proteins. S100A13 shares 83% and 90% amino acid identity with mouse and rat S100A13, respectively and plays a role in the export of proteins that lack a signal peptide. Like other S100 proteins, S100A13 is small and generally acidic with two EF-hand motifs that bind calcium ions with differing affinities. Composed of four amphiphilic helices, S100A13 is a homodimer that binds two calcium and one copper ion per subunit.