A novel rat 523 amino acid phosphophoryn: nucleotide sequence and genomic organization

Phosphophoryns (PP), the major noncollagenous proteins (NCPs) in dentin, ar e believed to play a crucial role in mineral nucleation and hydroxyapatite growth during dentin mineralization. Previously we identified two mature ra t PP transcripts. one coding for a 240 amino acid protein (designated as PP 240) (H.H. Ritchie, L.-H. Wang, J. Biol. Chem. 271 (1996) 21695-21698), and another coding for a 171 amino acid protein (PP171) (H.H. Ritchie, L. Wang , Biochim. Biophys. Acta 1493 (2000) 27-32). We now have identified a third novel dentin sialoprotein (DSP)-PP cDNA transcript that encodes a 523 amin o acid protein (PP523) with typical PP characteristics including DSS and DS motifs suitable as potential casein kinase I and II phosphorylation sites. Based on amino acid composition, the PP523 protein product is identical to native rat HP2. We also show that the PP523 sequence is identical to the c orresponding genomic DNA sequence. Taken together, the existence of multipl e DSP-PP transcripts. each significantly different from the other in net ne gative charge, suggests that dentin mineralization processes may be under f ine-tune control by these PP protein isoforms. (C) 2001 Elsevier Science B. V. All rights reserved.