Flaw in protein causes weakened enamel, study finds
WASHINGTON, U.S.: For some patients, no matter how diligent they are with their oral health, issues with their teeth seem to arise more easily than for others. In a new study, scientists have uncovered how a small flaw in a protein results in damaged enamel that is prone to decay. In the study, the researchers found that defective amelogenin proteins stick or bind abnormally tightly to the building enamel, failing to clear out when they should and hindering the growth process through which strong enamel is built.
The condition is known as amelogenesis imperfecta (AI) and those who suffer from it do not develop enamel correctly because of a single amino acid defect in the amelogenin. The genetic defect causes soft, discolored enamel that easily breaks. “The teeth aren’t as strong because the enamel is much thinner and the crystals less ordered,” said first author of the paper Dr. Jinhui Tao, from Pacific Northwest National Laboratory. “In most people, the enamel is the hardest substance in their body, but that’s not true for patients with AI.”
Tao and his colleagues wanted to see how strongly proteins stick to other substances and to each other, a process known as protein binding. In order to see this unfold in real time, the team combined atomic force microscopy with solid-state nuclear magnetic resonance spectroscopy, available through the Environmental Molecular Sciences Laboratory, as well as other methods to study mineralization and other processes involving the proteins that form enamel.
According to the study’s results, the defective proteins’ tendency to stick too long and too strongly to the surface disrupts other molecular players from doing their jobs in creating a solid crystalline structure. They also slow down an enzyme known as matrix metallopeptidase-20 (MMP20),which removes excess amelogenin from the developing mineral surface. When MMP20 cannot do its job, enamel grows more slowly and is weaker. The sticky proteins also slow down the formation of hydroxyapatite.
“This work helps us understand why people with these mutations have weak and fragile tooth enamel, but more broadly, it gives us important information about how to control the creation or manipulation of materials for many applications, such as the development of new organic–inorganic hybrid materials for high-performance computing, catalysis research, or energy storage,” Tao said.
The study, titled “The energetic basis for hydroxyapatite mineralization by amelogenin variants provides insights into the origin of amelogenesis imperfecta,” was published on July 9, 2019, in the Proceedings of the National Academy of Sciences of the United States of America.