A comparative study of sialic acid-rich proteins in rat bone and dentin

Four sialic acid-rich (SA-rich) proteins Found in bone and dentin, osteopon tin (OPN), bone sialoprotein (BSP), bone acidic glycoprotein-75 (BAG-75), a nd dentin matrix protein 1 (DMP1), share some common features. We used SDS- PAGE and Western immunoblots to analyze and compare SA-rich proteins in bon e and dentin extracts From rats with a single chromatographic procedure. OP N was detected in dentin extracts, with a relative level less than one-seve ntieth or that in bone. Both bone and dentin BSP demonstrated an extremely broad distribution pattern, probably due to a high degree of heterogeneity in post-translational modifications. BAG-75 in both bone and dentin was det ected as an 83 kDa band, dramatically distinct from that of DMP1. Using a p olyclonal antibody raised against a purified bone 57 kDa protein (a portion of DMP1), we detected 150 kDa protein bands in bone fraction; the same ban ds were recognized by antirecombinant rat DMP1 antibody. Bands from dentin migrating at about 150 kDa in earlier fractions and progressing to 200 kDa in later fractions showed a clear immunoreactivity to the anti-57 kDa antib ody. We conclude that the majority of DMP1 in rat bone is processed into fr agments, whereas that in dentin remains intact.