Sialoproteins of bone and dentin.

Osteopontin (OPN), bone sialoprotein (BSP) and bone acidic glycoprotein-75 (BAG-75), are sialoproteins isolated from bone extracts that resemble each other in size and composition. OPN and BSP contain an RGD sequence (not proven but possible for BAG-75), suggesting that their biological functions involve interaction with cell membrane integrins. Dentin has small amounts of OPN and BSP but also contains a major sialic acid-rich protein, DSP that has an overall composition similar to the bone sialoproteins. It is possible that DSP plays a similar biological role in dentin as OPN, BSP, and BAG-75 play in bone. Future experimentation should shed further light onto the potential relationships of the four sialoproteins.