S 100 P ( S 100 calcium binding protein P )

S100P protein consists of 95 amino acids with a molecular weight of 10.4 kDa. S100P is a Ca binding protein that belongs to S100 family ("Soluble in 100% saturated solution with ammonium sulfate") which was first isolated from human placenta and is therefore designated as "P". S100 family includes at least 26 members, which are thought to be expressed only in vertebrates and are present in a tissue and cell-specific manner. S100 proteins are characterized by common structural motifs including 2 EF-hands (helix-loop-helix calcium binding domains) with different affinities for calcium ions, a central hinge region and the C-terminal extension. The Nterminal half of the protein contains an unconventional EF hand that binds calcium with lower affinity, while the C-terminal is canonical and binds calcium with high affinity. The connecting hinge region and the Cterminal extension are the most variable regions and thus determine the functional specificity of S100 family members, including S100P. In addition to Ca, S100P also binds Zn and Mg and can form homoand heterodimers.