Dentin phosphoryns

Important molecules of this class are dentin phosphoryns or sialoproteins containing high aspartic acid (Asp) and extremely high serine (Ser) amoimts, which can be phosphorylated by the enzymes casein kinases I and II. Examples include rat dentin phosphoprotein with 43% Ser and 31% Asp [155], rat phosphoryn with 56% Ser and 32% Asp [ 156], hiunan dentin phosphophoryn with 58% Ser and 26% Asp [157] or a moUuscan shell glycoprotein with 32% Ser and 20% Asp [158]. It seems that phosphoserin (P-Ser) is of especial importance for polymer-crystal interactions, very Ukely in blocked sequences. In addition, the so-called Asprich proteins were recently identified in nacre and can contain up to 53 mol % Asp and 11% Glu [ 159,160]. 

The major non-collagenous components of the dentin matrix are highly-phosphorylated proteins, phosphoryns, with many phosphoserine and aspartate residues (Butler et al., 1992). Dentin contains fewer proteoglycans than predentin. The proteoglycans from predentin are degraded upon mineralization, while small proteoglycans and phosphoryns are excreted by odontoblasts and incorporated into dentin (Goldberg et al., 1987 Linde, 1989). 

Dimuzio, M. T., Veis, A. Phosphoryns-major noncollagenous proteins of rat incisor dentin. Calc. Tiss. Res. 25, 169 (1978)... 

Bone and teeth are composed of hydroxyapatite crystals [16,17] and the crystal axis of both is controlled by organic matrices, such as collagens, acidic peptides and peptide-glucans [18-20]. The acidic peptide is called phosphoryn and contains repeated Asp-Ser-Ser sequences, of which the Ser residues are totally phosphorylated (Fig. 1) [21]. Similarly, large munbers of Glu, Asp and Ser residues are found in peptide-glucan and dentin sialoprotein. These proteins are known to be essential for the calcification of hydroxyapatite crystals [18]. 

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