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

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

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  • 1Department of Preventative and Restorative Dental Sciences, University of California, 707 Parnassus Avenue, San Francisco, CA 94143, USA.

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.

PMID:
22974364
PMCID:
PMC3496023
DOI:
10.1021/bm300942c
[PubMed - indexed for MEDLINE]
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