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

摘要

Phosphophoryns (PP), the major noncollagenous proteins (NCPs) in dentin, are believed to play a crucial role in mineral nucleation and hydroxyapatite growth during dentin mineralization. Previously we identified two mature rat 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 (PP_(171)) (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 amino acid protein (PP_(523)) 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 PP_(523) protein product is identical to native rat HP2. We also show that the PP_(523) sequence is identical to the corresponding genomic DNA sequence. Taken together, the existence of multiple DSP-PP transcripts, each significantly different from the other in net negative charge, suggests that dentin mineralization processes may be under fine-tune control by these PP protein isoforms.