Dentin sialophosphoprotein (DSPP) is a major secretory product of odontoblasts and is critical for proper dentin formation. DSPP is believed to be processed into only two structural/functional domains: dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Here we report the isolation and characterization of a third domain of DSPP, designated dentin glycoprotein (DGP). DGP was isolated from a guanidine/EDTA extract of porcine tooth dentin by ion exchange, hydroxyapatite affinity, size

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... ion, and RP-HPL chromatography. Endoproteinase lysine C digestion products of DGP were characterized by Edman sequencing and mass spectrometry. The porcine DGP backbone is the 81-amino acid segment of DSPP (Ser 392 to Gly 472 ) between the DSP and DPP domains. DGP has four phosphorylated serine residues (Ser 453 , Ser 455 , Ser 457 , and Ser 462 ) and one glycosylated asparagine (Asn 397 ). There are no other posttranslational modifications. DGP is a stains-all positive protein with an apparent molecular mass on SDS-PAGE of 19 kDa, which is reduced by glycopeptidase A digestion to 16 kDa. A variety of glycans can be linked to Asn 397 . All are complex biantennary structures with a common N-linked pentasaccharide core (mannose 3 -Nacetylglucosamine 2 ), most with a fucosyl residue on the innermost N-acetylglucosamine. The ␣1-3 and ␣1-6 arms are always galactose ␤1-4 N-acetylglucosamine ␤1-2 mannose, and either or both arms can be unsialidated or monosialidated. The calculated monoisotopic molecular masses of the different glycosylated forms of the DGP phosphoprotein are: unsialidated 10,523 and 10,670, monosialidated 10,815 and 10,961, and disialidated 11,106, and 11,252 Da, with the disialidated forms being the most abundant.