George Anne, Hao Jianjun
Department of Oral Biology, University of Illinois, Chicago, Ill. 60612, USA.
Cells Tissues Organs. 2005;181(3-4):232-40. doi: 10.1159/000091384.
Mineral deposition is essential for the development of hard tissues like bone and teeth. In matrix-mediated mechanisms responsible for dentin formation, type I collagen defines the framework for mineral deposition and by itself is not sufficient to support nucleation of hydroxyapatite. However, in the presence of non-collagenous proteins, nucleation sites have been identified within the hole regions of the fibrils, and at these sites, mineral crystals can grow and propagate. Non-collagenous proteins constitute 5-10% of the total extracellular matrix proteins. They are embedded within the mineral deposits, suggesting a possible interaction with the mineral phase. During dentin formation, phosphophoryn (PP), an abundant macromolecule in the extracellular matrix, can initiate mineral deposition in localized regions by matrix-mediated mineralization mechanism. In our work, we have demonstrated that PP, due to its highly phosphorylated post-translational modification, can bind calcium ions with high affinity and at the same time aggregate collagen fibrils at the mineralization front. Molecular modeling has further demonstrated that the spacing of the carboxyl and phosphate groups present on PP might be essential for dictating the crystal orientation relative to the collagen substrate. Thus, PP may provide the interface linkage between mineral crystal and collagen fibrils.
矿物质沉积对于骨骼和牙齿等硬组织的发育至关重要。在负责牙本质形成的基质介导机制中，I型胶原蛋白为矿物质沉积定义了框架，但其本身不足以支持羟基磷灰石的成核。然而，在存在非胶原蛋白的情况下，已在原纤维的孔区域内确定了成核位点，并且在这些位点，矿物晶体可以生长和扩展。非胶原蛋白占细胞外基质蛋白总量的5-10%。它们嵌入在矿物质沉积物中，表明可能与矿物相相互作用。在牙本质形成过程中，磷蛋白（PP）是细胞外基质中一种丰富的大分子，可通过基质介导的矿化机制在局部区域启动矿物质沉积。在我们的工作中，我们已经证明，由于其高度磷酸化的翻译后修饰，PP可以高亲和力结合钙离子，同时在矿化前沿聚集胶原纤维。分子建模进一步表明，PP上存在的羧基和磷酸基团的间距可能对于决定晶体相对于胶原底物的取向至关重要。因此，PP可能提供矿物晶体与胶原纤维之间的界面连接。
