S100 family proteins are small (10-12 kDa), acidic proteins that are found exclusively in vertebrates. They belong to a highly conserved group of EF-hand calcium-binding molecules that consists of more than 25 members. They are the only EF-hand proteins that form both homodimeric and heterodimeric complexes. Although structurally related, their expression patterns and functions are usually distinct.
S100A10, also called p11, is a 97 amino acid member of the S100 family of EF hand proteins, but does not bind calcium. It is primarily found, either within or on the surface of mast cells, as a complex of two annexin A2 subunits with two S100A10 subunits. Extracellular S100A10 is a plasminogen receptor important for plasmin production and cellular invasiveness. Intracellular S100A10 may target ligands to the endoplasmic reticulum. Mouse S100A10 shows 92% amino acid identity with human S100A10.