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J. Biol. Chem., Vol. 283, Issue 21, 14835-14844, May 23, 2008

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Porcine Dentin Sialophosphoprotein

LENGTH POLYMORPHISMS, GLYCOSYLATION, PHOSPHORYLATION, AND STABILITY^*

Yasuo Yamakoshi, Yuhe Lu, Jan C.-C. Hu, Jung-Wook Kim^¶, Takanori Iwata^||, Kazuyuki Kobayashi^**, Takatoshi Nagano^**, Fumiko Yamakoshi, Yuanyuan Hu, Makoto Fukae, and James P. Simmer¹

From the Departments of Biologic and Materials Sciences and Orthodontics and Pediatric Dentistry, University of Michigan School of Dentistry, Ann Arbor, Michigan 48108, the ^¶Department of Pediatric Dentistry & Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea 110-768, the ^||Institute of Advanced Biomedical Engineering and Science, Tokyo Women's Medical University, Tokyo 162-8666, Japan, and the Departments of ^**Periodontics and Endodontics and Biochemistry, School of Dental Medicine, Tsurumi University, Yokohama 230-8501, Japan

Dentin sialophosphoprotein (DSPP) is critical for proper mineralization of tooth dentin, and mutations in DSPP cause inherited dentin defects. Dentin phosphoprotein (DPP) is the C-terminal cleavage product of DSPP that binds collagen and induces intrafibrillar mineralization. We isolated DPP from individual pigs and determined that its N-terminal and C-terminal domains are glycosylated and that DPP averages 155 phosphates per molecule. Porcine DPP is unstable at low pH and high temperatures, and complexing with collagen improves its stability. Surprisingly, we observed DPP size variations on SDS-PAGE for DPP isolated from individual pigs. These variations are not caused by differences in proteolytic processing or degrees of phosphorylation or glycosylation, but rather to allelic variations in Dspp. Characterization of the DPP coding region identified 4 allelic variants. Among the 4 alleles, 27 sequence variations were identified, including 16 length polymorphisms ranging from 3 to 63 nucleotides. None of the length variations shifted the reading frame, and all localized to the highly redundant region of the DPP code. The 4 alleles encode DPP domains having 551, 575, 589, or 594 amino acids and completely explain the DPP size variations. DPP length variations are polymorphic and are not associated with dentin defects.

Received for publication, January 24, 2008 , and in revised form, March 13, 2008.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) DPP₅₅₁, EU419998 [GenBank] ; DPP₅₇₅, EU419999 [GenBank] ; DPP₅₈₉, EU420000 [GenBank] ; and DPP₅₉₄, EU419997.

^* This work was supported, in whole or in part, by Grants DE15846 and DE11301 (NIDCR). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental sequence data.

¹ To whom correspondence should be addressed: Univ. of Michigan Dental Research Laboratory, 1210 Eisenhower Pl, Ann Arbor, MI 48108. Tel.: 734-975-9315; Fax: 734-975-9326; E-mail: jsimmer{at}umich.edu.

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