[5] BSP, a SIBLING protein, was originally isolated from bovine cortical bone as a 23-kDa glycopeptide with high sialic acid content.

[9] The mammalian BSP cDNAs encode for proteins averaging 317 amino acids, which includes the 16-residue preprotein secretory signal peptide.

BSP has been demonstrated to be extensively post-translationally modified, with carbohydrates and other modifications comprising approximately 50% of the molecular weight of the native protein.

[16][17] These modifications, which include N- and O-linked glycosylation, tyrosine sulfation and serine and threonine phosphorylation, make the protein highly heterogeneous.

The model suggests that the protein provides a flexible template for the rapid self-assembly of calcium and phosphate ions, so nucleating the growth of hydroxyapatite crystals.