Osteopontin (OPN)

Osteopontin (OPN), is a secreted multifunctional glyco-phosphoprotein with roles in bone metabolism, immune regulation, tissue remodeling , cell survival, and tumor progression . Gene structure and chromosomal location identify OPN as a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family that also includes BSP,BMP1,DSPP, ENAM and MEPE. Murine OPN issynthesized as a 294 amino acid (aa) precursor protein with a predicted 16 aa signal peptide and a highly unusual mature protein sequence, containing 68 acidic aa and 23 potential Ser/Thr phosphorylation sites. Although the predicted molecular weight of OPN is 31 kDa,phosphorylation and N- and O-glycosylation may allow it to appear as large as 75 kDa. Variability in post-translational modifications can influence the activity of OPN.