Characterization of biomineralization mechanism mediated by dentin matrix protein 1 in vitro

Biomineralization of bone and dentin is highly regulated by extracellular matrix secreted from the cells. 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 mechanisms of protein mediated mineral initiation are far from understood. The present thesis shows that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate hydroxyapatite in vitro in a multi-step process that begins by DMP1 binding calcium ions and initiating mineral deposition. Characterization of the functional domains in DMP1 demonstrated that inter-molecular assembly of acidic clusters into a beta-sheet template was essential for the observed mineral nucleation. Further studies showed that nascent calcium phosphate nuclei formed in solution were assembled into ordered protein-mineral complex with the aid of oligomerized DMP1. The interactions between DMP1 and type I collagen were examined comprehensively. It was demonstrated that specific binding of DMP1 on the collagen fibril might be a key step in collagen matrix organization and mineralization.; The current study demonstrates that formation of calcified tissues is a highly regulated process, involving a combination of both positive and negative events, i.e., prohibit spontaneous mineral precipitation and initiate temporally and spatially regulated mineral deposition. This initiation is highly dependent upon the formation of a preorganized template and molecular recognition functions. Such information is valuable and could be exploited for the synthesis of bone and dentin-like composites.