Self-assembly of filamentous amelogenin requires calcium and phosphate: from dimers via nanoribbons to fibrils

Biomacromolecules. 2012 Nov 12;13(11):3494-502. doi: 10.1021/bm300942c. Epub 2012 Sep 28.

Abstract

Enamel matrix self-assembly has long been suggested as the driving force behind aligned nanofibrous hydroxyapatite formation. We tested if amelogenin, the main enamel matrix protein, can self-assemble into ribbon-like structures in physiologic solutions. Ribbons 17 nm wide were observed to grow several micrometers in length, requiring calcium, phosphate, and pH 4.0-6.0. The pH range suggests that the formation of ion bridges through protonated histidine residues is essential to self-assembly, supported by a statistical analysis of 212 phosphate-binding proteins predicting 12 phosphate-binding histidines. Thermophoretic analysis verified the importance of calcium and phosphate in self-assembly. X-ray scattering characterized amelogenin dimers with dimensions fitting the cross-section of the amelogenin ribbon, leading to the hypothesis that antiparallel dimers are the building blocks of the ribbons. Over 5-7 days, ribbons self-organized into bundles composed of aligned ribbons mimicking the structure of enamel crystallites in enamel rods. These observations confirm reports of filamentous organic components in developing enamel and provide a new model for matrix-templated enamel mineralization.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amelogenin / chemistry*
  • Calcium / chemistry
  • Dental Enamel Proteins / chemistry*
  • Hydrogen-Ion Concentration
  • Microscopy, Atomic Force
  • Microscopy, Electron, Transmission
  • Nanotubes, Carbon
  • Phosphates / chemistry
  • Protein Multimerization*

Substances

  • Amelogenin
  • Dental Enamel Proteins
  • Nanotubes, Carbon
  • Phosphates
  • enamel matrix proteins
  • Calcium