enamel proteins Flashcards
describe the organisation of the enamel rod units
- Each ameloblast deposits a unit of the tissue
- each rod is composed of array of crystallites
- In parallel fashion
- each rod is composed of array of crystallites
- Unit is interlocking other units
- Crystallites run in different directions in the head and the rod tail
overall function of enamel proteins
function as nucleators and modulators of hydroxyapatite crystal formation
what processes are responsible for enamel formation?
- Enamel ECM synthesis and assembly
- Leads to initial mineralisation
- ECM processing and ultimately degradation
- Leads to final mineralisation of the process
- Supramolecular control of hydroxyapatite crystal formation and growth
what does enamel consist of?
how does this change?
- contains no collagen
- is composed of amelogenin and other specialized proteins
- which are largely replaced by hydroxyapatite crystals during the mineralization process:
- Mature enamel consists of:
- 96% inorganic hydroxyapatite mineral
- 4% water and organic components
what enamel protein groups are there?
when are the proteins expressed?
- Amelogenin
- part of enamel matrix deposited during enamel secretion,
- Ameloblastin
- part of enamel matrix deposited during enamel secretion,
- Enamelin
- part of enamel matrix deposited during enamel secretion,
- Amelotin
- only expressed from maturation stage onwards
- Apin/ODAM (odontogenic ameloblast associated protein)
- only expressed from maturation stage onwards
how are enamel proteins synthesised and released?
- Secretory ameloblasts are full of endoplasmic reticulum
- Highly biosynthetically active cells
- Apical end of secretory ameloblast
- Tomes process full of secretory granules
- proteins are synthesised in secretory granules
- released directly from the tomes process
which is the most abundant enamel matrix protein?
amelogenin
what types of amelogenin are there?
- Many different proteolytically processed TRAP
- tyrosine-rich amelogenin peptide
- Comprised of the end terminus of the amelogenin molecule
- Important role in final mature tissue
- and alternatively spliced products: LRAP
- Leucine-rich amelogenin peptide
- Shorter
- Contains a truncated version of the central domain
what is the function of amelogenin?
role in organising the framework of the tissue
how does amelogenin contribute to organising the framework of the tissue?
- Self-assembles into spherical structures containing many amelogenin molecules
- Size of nanospheres correlates to the spacing of the crystallites in the tissue
- amelogenin nanospheres interact with other components to form an organised structure
- binds tightly to enamel crystals
- regulates HAP crystal growth
- nanospheres promote growth in c-axis
- also prevent pre-mature crystal fusion
- binds tightly to enamel crystals
how does amelogenin promote growth in the c-axis
Crystals have 3 different phases - a b and c
- Amelogin nanospheres bind to b phase
- therefore, only way crystal can grow is in the c direction
- No amelogenin present
- = Grows in b and c direction
what is enamelysin
when is it expressed
where is it produced
where is it secreted from
what is its role
- AKA MMP-20
- expressed during
- secretory and transition stages of enamel development
- can be produced by
- ameloblasts and odontoblasts
- secreted from
- Tome’s process directly into enamel matrix
- function
- cleaves amelogenin
- role in quaternary organisation of nanospheres
- required for activation of proteinases - needed for mineralisation to occur
- cleaves amelogenin
what is the structure of enamelysin
how is it activated?
- Catalytic domain containing histidines
- important for coordinating with Zn ion
- Propeptide domain - regulatory domain
- Got cysteine
- Coordination of the zinc
- Got cysteine
- Activation of this proteinase happens by cleavage of the propeptide which allows active site to be exposed
- Cleavage occurs through proteolysis or activation by MT1-MMP
what is enamel matrix serine proteinase 1?
where is it expressed?
when is there the most EMSP1 activity?
what is it activated by?
- AKA kallikrein 4
- expressed in
- enamel, pulp, also prostate
- expression increases
- during transition stage
- elevated during maturation stage
- works optimally at pH 5.7
- activated by
- MMP-20 or cathepsin C
- cleave activation peptide
- MMP-20 present during early stages of enamel formation
- MMP-20 or cathepsin C
what is the role of EMSP1?
- Involved in bulk degradation of protein
- After degradation
- further mineralisation
- Increase thickness of mineral crystallites
is amelogenin required for mineral crystal initiation?
is amelogenin required for enamel organisation?
amelogenin is not required for mineral crystal initiation
amelogenin is essential for enamel organization
what can a mutation in kallikrein 4 cause?
Autosomal recessive hypomaturation AI
- Normal enamel thickness but enamel radiographically hypomineralised
- normal secretion but retention of enamel proteins reduces crystal growth
- Normal shaped crowns but discoloured in yellowish colour
- Have a rough surface
what is enamelin?
what is it expressed by?
what is its role?
Acidic glycoprotein which binds hydroxyapatite with high affinity
- expressed by
- only ameloblasts
- role
- interacts with crystallites
- involved in nucleation or elongatioin
what can mutations in enamelin cause?
- localised hypoplastic enamel pitting
- dominant trait
- severe hypoplasitc AI with open-bite malocclusion
- enamel layer absent
- exposure of dentine
- recessive trait
what is tuftelin
when is it expressed
- not a true enamel protein
- widely expressed in many tissues
- expressed
- very early in tooth expression
what is ameloblastin?
what is it composed of
where is it present?
what is its roles?
- amelin and sheathlin
- composed of
- two domains connected by flexible linker
- present
- near tomes process
- where it is secreted
- roles in
- regulating mineralisation
- required for adhesion between secretory ameloblasts and forming tissue
- required to maintain phenotype of ameloblasts
- ECM organisation
why are small quantities of proteins in hard tissues important?
hard tissues are prone to cracking
- Allows differential movement of adjacent rods
- Limited slippage between the rods reduces the stresses
- enamel is much more flexible than crystalline hydroxyapatite
