IBSP, is a monomeric non-collagenous member of the SIBLING family of extracellular matrix proteins. It is principally associated with the early stages of bone mineralization. Mouse IBSP is synthesized as a 324 amino acid (aa) precursor that contains a 16 aa signal sequence and a 308 aa mature region. The mature segment is divided into a basic N-terminus (aa 17-62), a central region (aa 63-233), and an acidic C-terminus (aa 234-317). IBSP is highly glycosylated, sulfated and phosphorylated. Phosphorylation promotes HAp nucleation, while carbohydrate may regulate cell adhesion.