Bone and dentin are closely allied tissues, formed when osteoblast or odontoblast cells secrete a type-1 collagen-rich non-mineralized extracellular matrix (ECM) which is subsequently mineralized by the deposition of apatite crystals. This process is controlled by a number of proteins, including members of the SIBLING (Small Integrin-Binding Ligand, N-linked Glycoprotein) family of non-collagen proteins (NCPs). Antibody studies have revealed SIBLINGs are subject to various PTMs (post-translational modifications) which control their function.The NCPs are thought to play an active role in the formation of bone and dentin, by regulating collagen fiber mineralization and apatite crystal growth. Although the exact function of some of these proteins remains elusive, the SIBLINGs have been researched in some detail, thanks to the efforts of antibody suppliers, like us at Novus Biologicals. Our SIBLING antibody database includes reagents targeting osteopontin (OPN), bone sialoprotein (BSP), dentin sialophosphoprotein (DSPP), and dentin matrix protein 1 (DMP1).The SIBLING proteins share a number of characteristics. They have the same chromosome location, and are expressed mainly in the bone and dentin, during synthesis of these tissues. All the proteins have the same RGD tripeptide (Arg-Gly-Asp) allowing cell-surface integrin binding, and the organisation of their gene exons is also similar. Importantly, they all undergo various post-translational modifications (PTMs) including phosphorylation, glycosylation, proteolytic processing and sulfation. Through these PTMs, SIBLING functions can be regulated and controlled.Through the products in our antibody catalog, researchers can probe the nature of SIBLING modifications in detail. One of the first to be reported was osteopontin phosphorylation, which occurs predominantly on serine residues and is catalyzed by casein kinase enzymes. Osteopontin antibody studies have revealed the protein has a diverse number of functions. It is a potent inhibitor of apatite mineralization, and regulates osteoclast function. However, although it is known phosphorylation is important to OPN function, the exact relevance is unknown.As we antibody suppliers add more antibodies to our SIBLING antibody databases, the nature and purpose of these modifications will become much clearer.