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J. Biol. Chem., Vol. 281, Issue 12, 8034-8040, March 24, 2006

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A Chondroitin Sulfate Chain Attached to the Bone Dentin Matrix Protein 1 NH₂-Terminal Fragment^*

Chunlin Qin¹, Bingzhen Huang, James N. Wygant, Bradley W. McIntyre, Charles H. McDonald^¶, Richard G. Cook^¶||, and William T. Butler

From the Department of Endodontics, University of Texas Houston Health Science Center Dental Branch, Houston, Texas 77030, Department of Immunology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, and ^¶Protein Chemistry Core Laboratory and ^||the Department of Immunology, Baylor College of Medicine, Houston, Texas 77030

Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein shown by gene ablations to be critical for the proper mineralization of bone and dentin. In the extracellular matrix of these tissues DMP1 is present as fragments representing the NH₂-terminal (37 kDa) and COOH-terminal (57 kDa) portions of the cDNA-deduced amino acid sequence. During our separation of bone noncollagenous proteins, we observed a high molecular weight, DMP1-related component (designated DMP1-PG). We purified DMP1-PG with a monoclonal anti-DMP1 antibody affinity column. Amino acid analysis and Edman degradation of tryptic peptides proved that the core protein for DMP1-PG is the 37-kDa fragment of DMP1. Chondroitinase treatments demonstrated that the slower migration rate of DMP1-PG is due to the presence of glycosaminoglycan. Quantitative disaccharide analysis indicated that the glycosaminoglycan is made predominantly of chondroitin 4-sulfate. Further analysis on tryptic peptides led us to conclude that a single glycosaminoglycan chain is linked to the core protein via Ser⁷⁴, located in the Ser⁷⁴-Gly⁷⁵ dipeptide, an amino acid sequence specific for the attachment of glycosaminoglycans. Our findings show that in addition to its existence as a phosphoprotein, the NH₂-terminal fragment from DMP1 occurs as a proteoglycan. Amino acid sequence alignment analysis showed that the Ser⁷⁴-Gly⁷⁵ dipeptide and its flanking regions are highly conserved among a wide range of species from caiman to the Homo sapiens, indicating that this glycosaminoglycan attachment domain has survived an extremely long period of evolution pressure, suggesting that the glycosaminoglycan may be critical for the basic biological functions of DMP1.

Received for publication, December 5, 2005 , and in revised form, January 12, 2006.

^* This work was supported by National Institutes of Health Grant DE 005092 (to C. Q.). 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.

¹ To whom correspondence should be addressed: Dept. of Endodontics, the University of Texas Houston Health Science Center Dental Branch, M. D. Anderson Blvd., DBB, Ste. 307, Houston, TX 77030. Tel.: 713-500-4583; Fax: 713-500-0497; E-mail: Chunlin.Qin{at}uth.tmc.edu.

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				C. Qin, R. D'Souza, and J.Q. Feng Dentin Matrix Protein 1 (DMP1): New and Important Roles for Biomineralization and Phosphate Homeostasis J. Dent. Res., December 1, 2007; 86(12): 1134 - 1141. [Abstract] [Full Text] [PDF]

				J.-W. Kim and J.P. Simmer Hereditary Dentin Defects J. Dent. Res., May 1, 2007; 86(5): 392 - 399. [Abstract] [Full Text] [PDF]