Characterization of extracellular and nascent dentin phosphoproteins

Experiments were designed to compare extracellular dentin phosphoprotein (DPP) and nascent DPP prior to post-translational modifications from several vertebrate species. Dental matrix proteins were extracted with acetic acid, followed by GuHCl-EDTA, and precipitated with CaCl2. Cross-reactivity of the DPPs with a mouse DPP antibody was determined by a dot-immunobinding assay. To analyze nascent DPP, mRNA was isolated from developing tooth organs and the mRNA-directed translation products were immunoprecipitated with the DPP specific antibody. All DPP components identified in the species which contained a DPP were shown to cross-react with the polyclonal mouse DPP antibody. The extracellular matrix DPPs were found to exhibit as much as a 30 kDa size difference using the same SDS PAGE system. In contrast, nascent DPPs were found to be the same size for all species examined. Our results indicate that differences in the molecular weight size of DPPs between species may be due to the degree of post-translational modifications such as phosphorylation.