DMP1 Binds Specifically to Type I Collagen and Regulates Mineral Nucleation and Growth

Abstract

Extracellular matrix of bone and dentin is highly complex and involves a dynamic process of deposition and removal. Cells are the main architect that build this designer matrix that is highly specialized to calcified tissues. Osteoblasts or odontoblasts secrete both collagen and noncollagenous proteins in a temporal and spatial manner. Type I collagen self-assembles and forms a fabric-like template onto which noncollagenous proteins and mineral bind in a well-regulated manner. Dentin matrix protein 1 (DMP1) is one such noncollagenous protein that contains several acidic groups that can bind calcium ions which in turn binds phosphate and initiates the calcification process. In this study, we demonstrate that DMP1 is localized at specific sites on the self-assembled collagen matrix of dentin. In vitro nucleation studies on demineralized and deproteinized dentin slice adsorbed with DMP1 show bundles of well-ordered needle-shaped nanohydroxyapatite deposited on the dentin matrix. The nucleated mineral structures had uniform length and width and their long axis was oriented parallel to the collagen fibril axis. Overall, the physiologically self-assembled collagen and DMP1 mediated ordered deposition of nanocrystalline HAP. Keywords Dentin matrix protein 1 · Collagen · Hydroxyapatite · Mineralization · Extracellular matrix 15.1 Introduction Biological composites such as bone, dentin, and cementum consist of a crystalline inorganic phase mainly carbonated hydroxyapatite embedded within a biopoly-meric organic matrix (Veis 1993; Veis and Dorvee 2013). The cells that produce these mineralized matrices exert a regulatory and exquisite control over the minerals they deposit, creating materials of varied shapes, sizes, and high tensile strength.