InterPro domain: IPR008412

This entry represents the bone sialoprotein II group of proteins.

The major non-collagenous matrix proteins (chondroitin-sulphate glycoproteins decorin and biglycan, sialoproteins osteopontin and bone sialoprotein, osteocalcin and osteonectin) have important roles in formation and organisation of the collagen matrix and nucleation and growth of hydroxyapatite crystals.

Bone sialoprotein (BSP) is a major structural protein of the bone matrix that is specifically expressed by fully differentiated osteoblasts [ 1 ], [ 2 ] and is highly specific for mineralising tissues. The expression of bone sialoprotein (BSP) is normally restricted to mineralised connective tissues of bones and teeth; it is thought to be responsible for nucleation of hydroxyapatite crystals. BSP also displays a high affinity for calcium ions. The mature protein has a molecular weight of around 33kDa and consists predominantly of Glu and Gly residues. It is subject to extensive posttranslational modification, and is predominantly phosphorylated at Ser residues. Posttranslational modifications can also cause BSP to act as an inhibitor of hydroxyapatite crystal formation. Ectopic expression of BSP occurs in various lesions, including oral and extraoral carcinomas, in which it has been associated with the formation of microcrystalline deposits and the metastasis of cancer cells to bone [ 3 ].

1. Characterization of the human bone sialoprotein (BSP) gene and its promoter sequence. Matrix Biol. 14, 31-40
2. Bone sialoprotein. Crit. Rev. Oral Biol. Med. 10, 79-98
3. Expression of bone sialoprotein in mineralized tissues of tooth and bone and in buccal-pouch carcinomas of Syrian golden hamsters. Arch. Oral Biol. 45, 551-62