# Amyloids in Enamel Development

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, SAN FRANCISCO · 2020 · $646,397

## Abstract

ABSTRACT
Amyloids are a class of proteins that spontaneously self-assemble into cross β-sheet aggregates which have
been associated with amyloidosis and neurodegeneration. However, recently, amyloids that are non-toxic and
rather play a functional role in a mammalian biosynthetic pathway have been discovered challenging our
current views on the sole role of amyloids in mammals to be cytotoxic. Here we propose that amelogenin, the
main protein of the developing enamel matrix, adapts cross-β sheet configuration and develops into fibrillar
amyloids to achieve structural support to guide mineralization in vivo and in vitro. Enamel, the hardest and
most mineralized tissue in the human body, is comprised of a unique organization of apatite nanofibers of
about 50 nm in diameter and several hundreds of micrometers in length. There is agreement that the unique
crystal morphology and organization into rod and interrod enamel is the result of a protein-guided uniaxial
growth process of apatite, but it is unclear by which molecular mechanisms this unique micro- and
nanostructure develops. While the role of self-assembly of enamel matrix proteins, in particular amelogenin,
has widely been recognized as a crucial factor in controlling the structural development of enamel, a
convincing relationship between organic supramolecular aggregates and enamel structure has only recently
been observed, when we discovered that the recombinant human full-length amelogenin protein (rH174) forms
ribbons of 17 nm in width, which grow to several micrometers in length. Such ribbons have the ability to self-
align and form bundles resembling the appearance of aligned apatite crystallites in an enamel rod. Analysis of
the primary structure of amelogenin revealed several domains with high propensity to form β-sheets, including
the possibilty to form amyloids, and produced a 14 residue N-terminal peptide (14P2) that readily assembled
into nanoribbons (6.7nm wide), with possible amyloid structure.
Amyloid stains were positive in enamel from mice lacking the enamel-specific enzyme kallikrein 4 (KLK4). Both
enamel tissue and recombinant amelogenin nanoribbons showed x-ray diffraction spacings at 4.7Å
characteristic of β sheets and amyloids. Enzymatic processing of self-assembled amelogenin promoted
precise cleavage into the 23 kDa and 20 kDa fragments which resisted further degradation by MMP-20, thus
possibly providing a stable organic template for mineralization during secretory stage amelogenesis, whereas
the second enamel protease is able to disassemble and to degrade amelogenin amyloids. Herein we will
further investigate the presence of amyloids in enamel and propose that amyloids play a key role in the
development and organization of the organic matrix of enamel and that an exploration of such structures is
essential to our understanding of enamel formation, its diseases and repair.

## Key facts

- **NIH application ID:** 9965887
- **Project number:** 5R01DE025709-05
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
- **Principal Investigator:** Stefan Friedrich Habelitz
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $646,397
- **Award type:** 5
- **Project period:** 2016-07-01 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9965887

## Citation

> US National Institutes of Health, RePORTER application 9965887, Amyloids in Enamel Development (5R01DE025709-05). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/9965887. Licensed CC0.

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