Single-Molecule Determination of the Face-Specific Adsorption of Amelogenin's C-Terminus on Hydroxyapatite

摘要

The energetics of protein-mineral interactions is a crucial but poorly characterized factor underlying the hierarchical structure of mineralized tissue. During mineralization, organized protein matrices direct formation of mineral components. As with all assembly processes, the free-energy change provides the underlying thermodynamic driver, in this case reflecting protein interactions with the nascent mineral. However, despite the importance of obtaining face-specific free energies of mineral binding to establish a molecular-level understanding of biomineral organization, to date no direct measurements have been reported. Computational approaches struggle with the complexities of proteins, the inadequacies of model water potentials and effects of background electrolytes. Herein we present a novel application of force spectroscopy in which an atomic force microscopy (AFM) tip, functionalized with Amelogenin protein (Amel) C-terminal fragment, is used to directly determine the single-molecule, face-specific free energy ΔG_B of Amel binding to hydroxyapatite (HAp), the mineral phase in tooth enamel. We then use complementary molecular dynamics (MD) simulations to compare binding energies at different faces and surface terminations and to identify the key interactions controlling face-specific binding and crystal morphology.