An important part of the answer appears in a report in the latest issue of Science.
The puzzle of enamel formation centers on amelogenin, a protein secreted by cells in gum tissue called ameloblasts. Amelogenin's closest analogue in the human body is collagen, the protein that guides the formation of mineral in bone.
Unlike collagen - which remains an essential part of bone structure, helping it to heal after fractures - amelogenin degrades and disappears during the process of enamel mineral growth, or biomineralization.
Because its transient role makes it hard to study, amelogenin has not been well understood despite investigations stretching over many years, said Janet Moradian-Oldak, a professor in the University of Southern California School of Dentistry and the paper's lead author. USC Postdoctoral research associate Chang Du contributed to the paper.
By its nature, amelogenin cannot form a lasting platform or scaffold for enamel development. The question is: can a protein with a very short life span provide a reliable structure for biomineralization?
The answer is yes, according Oldak and her team, whose discovery was serendipitous.
The researchers, in collaboration with Giuseppe Falini at the Universita di Bologna in Italy, had been attempting to study amelogenin by crystallizing it. Crystallography is a traditional method of exploring molecular structure.
After a year, the researchers were unable to obtain amelogenin crystals. Instead, their efforts produced what looked, under a microscope, like long, fettucine-like fibers. The fibers consisted of chains of amelogenin nanospheres: tiny balls of amelogenin molecules.
Oldak called the fibers "microribbons." She was struck by the similarity in structure between the ribbons and the calcium hyd
Contact: Carl Marziali
University of Southern California