Objectives:Dentin is formed when odontoblasts secrete a type I collagen-rich extracellular matrix, termed predentin, which is subsequently mineralized when apatite crystals are deposited. In addition to type I collagen, the extracellular matrix (ECM) of dentin contains a number of non-collagenous proteins and proteoglycans Dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1) belong to one category of non-collagenous proteins referred to as the SIBLING family. DSPP and DMP1 have been shown to be critical for dentinogenesis. Mutations in the Dspp gene are associated with dentinogenesis imperfecta type II and III while knockout of the Dmp1 gene results in dramatic defects in dentin mineralization. It is widely believed that the functions of DSPP and DMP1 are dependent on the nature and extent of posttranslational modifications including proteolytic processing, glycosylation and phosphorylation. Both DSPP and DMP1 in the ECM of dentin and / or bone are processed into NH2-terminal and COOH-terminal fragments; the NH2-terminal fragments of both proteins have a high level of glycosylation while their COOH-terminal fragments possess a large number of phosphates.
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