Supramolecular Assembly of Amelogenin Nanospheres into Birefringent Microribbons

Abstract

Although both tooth enamel and bone are composed of organized assemblies of carbonated apatite crystals, enamel is unusual in that it does not contain collagen nor does it remodel. Self-assembly of amelogenin protein into nanospheres has been recognized as a key factor in controlling the oriented and elongated growth of carbonated apatite crystals during dental enamel biomineralization. We report the in vitro formation of birefringent microribbon structures that were generated through the supramolecular assembly of amelogenin nanospheres. These microribbons have diffraction patterns that indicate a periodic structure of crystalline units along the long axis. The growth of apatite crystals orientated along the c axis and parallel to the long axes of the microribbons was observed in vitro. The linear arrays (chains) of nanospheres observed as intermediate states before the microribbon formation give an important indication as to the function of amelogenin in controlling the oriented growth of apatite crystals during enamel mineralization.

The nucleation and growth of calcium phosphate by amelogenin

“…Although amelogenin is relatively hydrophobic compared to other nucleation proteins, the supramolecular assembly of protein monomers into nanospheres, as demonstrated previously [8] and as demonstrated by AFM under these solution conditions (data not shown), is thought to concentrate the charged domain of the protein at the nanosphere surface [35] as shown schematically in Fig. 5.…”

“…Another recent study showed that amelogenin nanospheres could assemble to form ribbon-like structures by hanging drop crystallization in the presence of polyethylene glycol (PEG) and various salt solutions [35]. It was found that HAP grew with the c-axis parallel to the long axis of the microribbons when the surface immobilized ribbons were exposed to supersaturated solutions containing 2.5 mM calcium.…”

Identification of the functional activity of the [A-4] amelogenin gene splice product in newborn mouse ameloblasts

“…Amelogenin, the principal structural protein of the enamel organic matrix, is synthesized, secreted, and deposited into the extracellular matrix of ameloblasts during the well-defined secretory stage of ameloblast maturation. A current hypothesis suggests that, in vivo, amelogenin molecules aggregate into nanospheres, which assemble to form the structural scaffold for the deposition of apatite crystals (3,4). Extracellular deposition of amelogenin occurs in the space surrounding the Tome's processes.…”

Amelogenin expression in long bone and cartilage cells and in bone marrow progenitor cells

“…They comprise 90% of the developing extracellular enamel matrix proteins (Termine et al, 1980) and play a major role in the biomineralization and structural organization of enamel (Robinson et al, 1998;Fincham et al, 1999). Amelogenins are hydrophobic molecules that self-assemble in vitro and in vivo into nanospheric structures, which regulate the oriented and elongated growth, shape, and size of the enamel mineral crystal (Fincham et al, 1994;Du et al, 2005). During enamel development and mineralization, the abundant secreted amelogenins in the extracellular enamel are sequentially and discretely degraded by specific proteases, the metalloprotease Enamelysin (MMP20) and the serine protease EMSP1 (KLK4) (Simmer and Hu, 2002).…”