Recombinant Mouse IBSP/Sialoprotein II Protein, CF

IBSP (integrin‑binding sialoprotein; also BSP or bone sialoprotein II) is a 55 ‑ 75 kDa, secreted, variably glycosylated, monomeric non‑collagenous member of the SIBLING family of extracellular matrix (ECM) proteins (1 ‑ 3). It is principally associated with the early stages of bone mineralization. Mouse BSP is synthesized as a 324 amino acid (aa) precursor that contains a 16 aa signal sequence and a 308 aa mature region (4 ‑ 6). 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) (7). Functional segments associated with the mature molecule include a type I collagen binding domain (aa 19 ‑ 46), two non‑RGD cell binding sites (aa 30 ‑ 57 and 261 ‑ 281), an RGD alpha_v beta₃ integrin‑binding site (aa 286 ‑ 288) and  two regions that are potential hydroxyapatite (HAp) nucleation domains (aa 76 ‑ 83 and 151 ‑ 158) (3, 4, 8 ‑ 12). HAp formation requires a BSP nucleation site composed of at least eight consecutive glutamic acid residues and, likely, a contribution from a BSP‑associated conucleator (10, 13). BSP is highly glycosylated, sulfated and phosphorylated. Phosphorylation promotes HAp nucleation, while carbohydrate may regulate cell adhesion (1, 3, 14). Interaction with integrins stimulates cell migration and survival, and has been implicated in bone metastasis of cancers, especially those of breast and prostate (15). Mature mouse BSP shares 90% aa identity with rat, 70% with human, 67% with canine, equine and porcine, and 64% with bovine BSP, respectively. BSP is synthesized by megakaryocytes/platelets, osteoblasts, osteocytes, odontoblasts, osteoclasts and bone marrow stromal cells (16 ‑ 19).