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A multi-disciplined approach to understand the structural, spatial, and temporal features guiding amelogenin’s transformation of calcium phosphate into enamel


EMSL Project ID
60284

Abstract

One of nature’s hardest materials is enamel, which is 95% (by weight) carbonated hydroxyapatite (HAP). The exceptional functional properties of enamel arise from its intricate hierarchical structure and cannot be reproduced in vitro inorganically. In vivo the formation of enamel depends on amelogenin, the predominant protein in the enamel matrix. While amelogenin’s importance in enamel formation is widely accepted, the mechanism of growth and control at a molecular level is not established. In vitro studies suggest that amelogenin self-assembles in a stepwise process, forming dimers, followed by oligomers, and then nanospheres (20-100 monomers). The nanosphere structure is the most common structure observed in solution, however, it is in an equilibrium between structures that can be interrupted by changes in pH, the presence of a surface, or the presence of calcium and phosphate ions in solution, all conditions which vary during enamel formation. We hypothesize that the structure of amelogenin controls its interactions with minerals and the resulting mineral properties. Understanding the relevant amelogenin-mineral interactions necessitates developing a sub-nanometer scale, spatially resolved view of both metastable and stable phases of calcium phosphate minerals, the boundaries between these phases, and the distribution of amelogenin within and/or around them directing transformation from initial calcium phosphate clusters to HAP ribbons. Beyond mapping, a molecular-level understanding of the residues essential to mineral binding and the dynamic changes in amelogenin’s structure that dictate protein-protein and protein-HAP interactions through the stages of calcium phosphate mineral growth is desperately lacking. We propose to fill these significant gaps in our knowledge of the amelogenin-HAP interface during enamel growth with a suite of advanced characterization tools that include cryo-TEM, Raman spectroscopy, atomic force microscopy (AFM), scanning transmission X-ray microscopy (STXM), near-edge X-ray adsorption fine-structure spectroscopy (NEXAFS), small angle X-ray scattering (SAXS), NMR spectroscopy (solution and solid state), and atomic probe tomography (APT). The data accumulated in our pursuit will be rigorously analyzed through the lenses of the latest molecular dynamics, molecular modeling, and artificial intelligence tools.

Project Details

Start Date
2022-02-24
End Date
2022-09-30
Status
Closed

Team

Principal Investigator

Garry Buchko
Institution
Pacific Northwest National Laboratory

Team Members

Sebastian Mergelsberg
Institution
Pacific Northwest National Laboratory

Jinhui Tao
Institution
Pacific Northwest National Laboratory

Sandra Taylor
Institution
Pacific Northwest National Laboratory

Arun Devaraj
Institution
Pacific Northwest National Laboratory

Bojana Ginovska
Institution
Pacific Northwest National Laboratory

Wendy Shaw
Institution
Pacific Northwest National Laboratory