IBSP
Description
The IBSP (integrin binding sialoprotein) is a protein-coding gene located on chromosome 4.
Bone sialoprotein (BSP) is a key component of mineralized tissues, including bone, dentin, cementum, and calcified cartilage. It contributes significantly to the bone extracellular matrix, comprising roughly 8% of all non-collagenous proteins found in bone and cementum. BSP, a SIBLING protein, was initially isolated from bovine cortical bone as a 23-kDa glycopeptide with a high sialic acid content. The human variant of BSP is known as bone sialoprotein 2 (IBSP), also referred to as cell-binding sialoprotein or integrin-binding sialoprotein. It is encoded by the IBSP gene.
Native BSP has an apparent molecular weight of 60-80 kDa based on SDS-PAGE, which deviates significantly from the predicted weight (based on cDNA sequence) of approximately 33 kDa. Mammalian BSP cDNAs encode proteins averaging 317 amino acids, including a 16-residue preprotein secretory signal peptide. Among the characterized mammalian cDNAs, there is approximately 45% conservation of sequence identity, with an additional 10-23% conservative substitution. BSP is highly acidic (pKa of ~ 3.9) and contains a high proportion of Glu residues, constituting approximately 22% of the total amino acids. Secondary structure prediction and hydrophobicity analyses suggest an open, flexible structure for BSP, with potential for regions of α-helix and some β-sheet. However, most studies using 1D NMR and circular dichroism have shown that BSP lacks α-helical or β-sheet structure.
IBSP binds tightly to hydroxyapatite, forming an integral part of the mineralized matrix. It plays a crucial role in cell-matrix interactions, promoting adhesion and migration of various cells via the alpha-V/beta-3 integrin receptor (ITGAV:ITGB3).
IBSP is also known as BNSP, BSP, BSP-II, SP-II.
