Bone sialoprotein 2 (Ibsp) is an anionic phosphorylated glycoprotein expressed almost exclusively in mineralized tissues. It is a potent nucleator of hydroxyapatite formation. The binding of IBSP to collagen is thought to be important for the initiation of bone mineralization and in the adhesion of bone cells to the mineralized matrix (Fujisawa et al. 1995, Tye et al. 2005).