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J. Biol. Chem., Vol. 279, Issue 12, 11649-11656, March 19, 2004

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Dentin Matrix Protein 1 Immobilized on Type I Collagen Fibrils Facilitates Apatite Deposition in Vitro^*

Gen He and Anne George

From the Department of Oral Biology, University of Illinois at Chicago, Chicago, Illinois 60612

During bone and dentin mineralization, the crystal nucleation and growth processes are considered to be matrix regulated. Osteoblasts and odontoblasts synthesize a polymeric collagenous matrix, which forms a template for apatite initiation and elongation. Coordinated and controlled reaction between type I collagen and bone/dentin-specific noncollagenous proteins are necessary for well defined biogenic crystal formation. However, the process by which collagen surfaces become mineralized is not understood. Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein expressed during the initial stages of mineralized matrix formation in bone and dentin. Here we show that DMP1 bound specifically to type I collagen, with the binding region located at the N-telopeptide region of type I collagen. Peptide mapping identified two acidic clusters in DMP1 responsible for interacting with type I collagen. The collagen binding property of these domains was further confirmed by site-directed mutagenesis. Transmission electron microscopy analyses have localized DMP1 in the gap region of the collagen fibrils. Fibrillogenesis assays further demonstrated that DMP1 accelerated the assembly of the collagen fibrils in vitro and also increased the diameter of the reconstituted collagen fibrils. In vitro mineralization studies in the presence of calcium and phosphate ions demonstrated apatite deposition only at the collagen-bound DMP1 sites. Thus specific binding of DMP1 and possibly other noncollagenous proteins on the collagen fibril might be a key step in collagen matrix organization and mineralization.

Received for publication, August 21, 2003 , and in revised form, December 10, 2003.

^* This study was supported by National Institutes of Health Grants DE 13836 and DE 11657. 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.

To whom correspondence should be addressed: Dept. of Oral Biology (M/C 690), University of Illinois at Chicago, Chicago, IL 60612. E-mail: anneg{at}uic.edu.

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