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BDS 2: Oral Ecosystems > OE L10 Enamel Proteins > Flashcards

OE L10 Enamel Proteins Flashcards

1
Q

Where are the ameloblasts in direct contact with the crystallites?

A

At the apical end of the rod.
Deposition of mineral occurs perpendicular to the surface creating a rod tail, small amount from ameloblast edges creates interrod enamel.

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2
Q

Do crystallites run in the same direction in the rod tail and rod head?

A

No, crystallites run in different directions in the rod tail and rod head.

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3
Q

What do crystallites look like at the secretory stage compared to the maturation stage?

A

Secretory stage: extremely thin

Maturation stage: thick

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4
Q

Are hydroxyapatite crystals in enamel the same as those found in dentine and bone?

A

No.

  • Crystals in enamel are tens to hundreds of um long, have an aspect ratio (length/width) of at least 1000
  • Crystals in dentine and bone are usually only 100nm in length and only a few nm in width
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5
Q

What is the overall role of enamel proteins?

A

Enamel proteins act as nucleators and modulators of hydroxyapatite formation.
Specialised proteins which are largely replaced by HAP crystals during mineraliastion.

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6
Q

What term describes a tissue composed of both organic and inorganic materials?

A

A bioceramic.

Enamel is a non-collagenous bioceramic.

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7
Q

What are the 3 biological processes in creating enamel?

A
  1. Enamel ECM synthesis and assembly
  2. ECM proccesing and ultimate degradation
  3. Supramolecular control of HAP crystal formation and growth
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8
Q

Are there specific genes related to the mineralisation of enamel?

A

No, however, the overall genetic programme controls the timing and relative quanities of genes transcribed, proteins are translated and assemble into a matrix, this matrix guides crystal formation.

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9
Q

When does HAP mineral formation occur?

A
  • During assembly of the matrix

- During modification of the matrix

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10
Q

What is the origin of enamel?

A

Oral epithelial origin.

VS dentine which is derived from mesenchyme and neural crest and can be regenerated.

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11
Q

What are the 5 enamel specific proteins that have arisen from gene duplication?

A
  • Amelogenin
  • Ameloblastin
  • Enamelin
  • Amelotin
  • Apin/ODAM
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12
Q

What family do these 5 proteins belong to?

A

The secretory calcium-binding phosphoprotein family (SCPP)

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13
Q

Which enamel proteins are synthesised during secretion?

A
  • Amelogenin
  • Ameloblastin
  • Enamelin
    Form the enamel matrix template
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14
Q

Which enamel proteins are synthesised from maturation and onwards?

A
  • Amelotin
  • Apin/ODAM
    Synthesised at transition between maturation stage and the reduced enamel epithelium
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15
Q

How are enamel proteins synthesised and secreted?

A
  • Proteins synthesised in same vesicles and released (e.g. amelotin and apin in same vesicle).
  • Vesicles released from Tomes process
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16
Q

Describe the main features of amelogenin.

A
  • Most abundant enamel matrix protein (80-90%)
  • Expressed from genes on X and Y chromosomes, critical copy on X chromosome
  • Can isolate DNA from teeth to determine sex, single type of amelogenin = female, 2 types = male
17
Q

What are the 2 forms of amelogenin?

A
  • TRAP: proteolytically processed form

- LRAP: alternatively spliced products of amelogenin

18
Q

Describe the domain structure of an amelogenin molecule.

A
  • Rigid central domain made of proline, histidine and glutamine
  • N-terminal tri-tyrosine domain
  • C-terminal hydrophobic segmenet followed by mineral binding hydrophilic domain
19
Q

Describe the assembly of amelogenin molecules.

A
  • Amelogenin self-assembles into spherical structures containing many amelogenin molecules
  • One sphere usually contains 50-100 amelogenin molecules
  • Spheres are called nanospheres
  • Size of nanospheres corresponds to spacing of crystallites in the tissue, suggest amelogenin plays a role in organising the framework of the enamel
20
Q

What does the tri-tyrosine motif of amelogenin bind?

A

Binds to carbohydrates such as N-acetyl-glucosamine. Allows amelogenin to interact with other matrix components such as enamelins.

21
Q

What does the C-terminal domain of amelogenin bind to?

A

Binds to hydroxyapatite. Changes size of crystals and produces crystals of a very unique aspect ration (long and thin).

22
Q

What faces do crystals have?

A

3 faces.

  • A: top face covered in water
  • B: side face with amelogenin bound to it
  • C: if both A and B phases are occupied, the crystal must grow in C direction (along C-axis)

Explains unusually long crystallites.

23
Q

What 2 sets of proteinases are present in enamel development and when?

A
  • Metalloproteinases: active during secretory stage

- Serine proteinases: active during maturation stage

24
Q

Why are proteinases important in mineralisation?

A

Proteinases drive maturation by degrading proteins that inhibit mineral deposition.

25
Q

Give an example of a matrix metalloproteinase and its basic features.

A

Enamelysin (MMP-20)

  • Expressed primarily during secretory and transition stages
  • Produced by ameloblasts and odontoblasts
  • Secreted from secretory face of Tomes’ process
  • Cleaves amelogenin
  • Cleaves Kallikrein 4
26
Q

Give an example of a serine proteinase and its basic features.

A

Enamel matrix serine proteinase 1 (Kallikrein 4)

  • Cleaved by MMP-20 to be activated
  • Activity is pH sensitive (5.7)
  • Allows crystals to now grow in thickness instead of just length as it was doing before
27
Q

Describe knockout mice studies for 2 mutations in enamelysin.

A
  • Heterozygous: 50% normal proteloytic activity, sufficient for normal enamel formation
  • Homozygous: no proteolytic activity, amelogenin remains in tissue and prevents mineralisation from taking place
28
Q

In humans, what is the result of a mutaion affecting the hemopexin domain of enamelysin.

A

Recessive hypomaturation amelogenesis imperfecta.

  • Normal sized crowns
  • Dull, brownish coloured teeth
  • Little difference in radiotranslucency of dentine and enamel (shows that enamel is significantly under mineralised)
29
Q

Overall function of enamelysin (MMP-20)

A

Activation of proteases to then cause bulk degradation of protein and allow for mineralisation.
Without MMP-20 mineralisation cannot occur.

30
Q

What is the result of mutations in EMSP 1 (Kallikrein 4).

A

Autosomal recessive hypomaturation amelogenesis imperfecta.

  • Both alleles must be affected
  • Dramatic under mineralisation
  • Normal shaped crowns
  • Teeth yellow/brown
  • Teeth have rough surface
  • Teeth wear rapidly
31
Q

What is the result of mutations in enamelin.

A

2 types

  • Autosomal dominant amelogenesis imperfecta: hypoplastic enamel pitting
  • Autosomal recessive amelogenesis imperfecta: majority enamel absent, exposed dentine, open bite malocclusion as secondary consequence of hypersensitivity
32
Q

Describe the structure and functions of enamelin.

A
  • Synthesised during secretory phase
  • Large acidic protein
  • High affinity for HAP
  • Suggested to interact with crystallites and possibly be involved in nucleation or elongation
33
Q

What is tuftelin?

A
  • Not a true enamel protein

- Found at ADJ, not enamel specific and widely expressed in other tissues

34
Q

Describe the main features of ameloblastin.

A
  • Synthesised during secretory phase contributes to enamel matrix
  • 2 domains connected by flexible linker
  • Functions as an ECM organiser and an adhesion molecule for secretory ameloblasts binding to forming tissue
  • Maintains phenotype of ameloblasts
35
Q

What is the result of mutations in ameloblastin?

A

Recessive hypoplastic amelogenesis imperfecta:

- Teeth have rough surface

36
Q

What is the distribution of amelogenin, ameloblastin and enamelin in the enamel?

A
  • N-terminus amelogenin is present throughout the entire tissue
  • C-terminus amelogenin is only present in the outer layer of enamel, near the ameloblasts
  • Ameloblastin is present throughout the entire tissue (13-17 kDa form) in the sheath space between rods
  • Enamelin is only present within the rod core
37
Q

How do enamel proteins and minor organic components support the overall tissue?

A

Presence of minor inorganic components e.g. enamel proteins, allows differential movement between adjacent rods therefore reducing stress of the tissue.
Profound plasticing effect. Prevents cracks/fractures.

BDS 2: Oral Ecosystems (42 decks)

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