ENAM | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
Aliases | ENAM , AIH2, AI1C, ADAI, enamelin | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 606585 MGI: 1333772 HomoloGene: 9698 GeneCards: ENAM | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Enamelin | |||||||||
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Identifiers | |||||||||
Symbol | Enamelin | ||||||||
Pfam | PF15362 | ||||||||
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Enamelin is an enamel matrix protein (EMPs), that in humans is encoded by the ENAM gene. [5] [6] It is part of the non-amelogenins, which comprise 10% of the total enamel matrix proteins. [7] It is one of the key proteins thought to be involved in amelogenesis (enamel development). The formation of enamel's intricate architecture is thought to be rigorously controlled in ameloblasts through interactions of various organic matrix protein molecules that include: enamelin, amelogenin, ameloblastin, tuftelin, dentine sialophosphoprotein, and a variety of enzymes. Enamelin is the largest protein (~168kDa) in the enamel matrix of developing teeth and is the least abundant (encompasses approximately 1-5%) of total enamel matrix proteins. [6] It is present predominantly at the growing enamel surface.
Enamelin is thought to be the oldest member of the enamel matrix protein (EMP) family, with animal studies showing remarkable conservation of the gene phylogenetically. [8] All other EMPs are derived from enamelin, such as amelogenin. [9] EMPs belong to a larger family of proteins termed 'secretory calcium-binding phosphoproteins' (SCPP). [10]
Similar to other enamel matrix proteins, enamelin undergoes extensive post-translational modifications (mainly phosphorylation), processing, and secretion by proteases. Enamelin has three putative phosphoserines (Ser54, Ser191, and Ser216 in humans) phosphorylated by a Golgi-associated secretory pathway kinase (FAM20C) based on their distinctive Ser-x-Glu (S-x-E) motifs. [11] The major secretory product of the ENAM gene has 1103 amino acids (post-secretion), and has an acidic isoelectric point ranging from 4.5–6.5 (depending on the fragment). [12]
At the secretory stage, the enzyme matrix metalloproteinase-20 (MMP20) proteolytically cleaves the secreted enamelin protein immediately upon release, into several smaller polypeptides; each having their own functions. However, the whole protein (~168 kDa) and its largest derivative fragment (~89 kDa) are undetectable in the secretory stage; these are existent only at the mineralisation front. [7] Smaller polypeptide fragments remain embedded in the enamel, throughout the secretory stage enamel matrix. These strongly bind to the mineral and arrest seeded crystal growth.
The primary function of the proteins acts at the mineralisation front; growth sites where it is the interface between the ameloblast plasma membrane and lengthening extremity of crystals. The key activities of enamelin can be summarised:
It is speculated that this protein could interact with amelogenin or other enamel matrix proteins and be important in determining growth of the length of enamel crystallites. The mechanism of this proposed co-interaction is synergistic ("Goldilocks effect"). With enamelin enhancing the rates of crystal nucleation via the creation of addition sites for EMPs, such as amelogenin, to template calcium phosphate nucleation. [14]
It is best thought to understand the overarching function of enamelin as the proteins responsible for correct enamel thickness formation.
Mutations in the ENAM gene can cause certain subtypes of amelogenesis imperfecta (AI), a heterogenous group of heritable conditions in which enamel in malformed. [15] Point mutations can cause autosomal-dominant hypoplastic AI, and novel ENAM mutations can cause autosomal-recessive hypoplastic AI. [16] [17] However, mutations in the ENAM gene mainly tend to lead to the autosomal-dominant AI. [13] The phenotype of the mutations are generalised thin enamel and no defined enamel layer. [7]
A moderately higher than usual ENAM expression leads to protrusive structures (often, horizontal grooves) on the surface of enamel, and with high transgene expression, the enamel layer is almost lost. [18]
Ameloblasts are cells present only during tooth development that deposit tooth enamel, which is the hard outermost layer of the tooth forming the surface of the crown.
Amelogenins are a group of protein isoforms produced by alternative splicing or proteolysis from the AMELX gene, on the X chromosome, and also the AMELY gene in males, on the Y chromosome. They are involved in amelogenesis, the development of enamel. Amelogenins are type of extracellular matrix protein, which, together with ameloblastins, enamelins and tuftelins, direct the mineralization of enamel to form a highly organized matrix of rods, interrod crystal and proteins.
Ameloblastin is an enamel matrix protein that in humans is encoded by the AMBN gene.
Tuftelin is an acidic phosphorylated glycoprotein found in tooth enamel. In humans, the Tuftelin protein is encoded by the TUFT1 gene. It is an acidic protein that is thought to play a role in dental enamel mineralization and is implicated in caries susceptibility. It is also thought to be involved with adaptation to hypoxia, mesenchymal stem cell function, and neurotrophin nerve growth factor mediated neuronal differentiation.
The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum. The enamel organ is responsible for the formation of enamel, initiation of dentine formation, establishment of the shape of a tooth's crown, and establishment of the dentoenamel junction.
Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis forms a first layer of dentin. Dentin must be present for enamel to be formed. Ameloblasts must also be present for dentinogenesis to continue.
Dentinogenesis imperfecta (DI) is a genetic disorder of tooth development. It is inherited in an autosomal dominant pattern, as a result of mutations on chromosome 4q21, in the dentine sialophosphoprotein gene (DSPP). It is one of the most frequently occurring autosomal dominant features in humans. Dentinogenesis imperfecta affects an estimated 1 in 6,000-8,000 people.
Amelogenin, Y isoform is a protein that in humans is encoded by the AMELY gene. AMELY is located on the Y chromosome and encodes a form of amelogenin. Amelogenin is an extracellular matrix protein involved in biomineralization during tooth enamel development.
Amelogenin, X isoform is a protein that in humans is encoded by the AMELX gene. AMELX is located on the X chromosome and encodes a set of isoforms of amelogenin by alternative splicing. Amelogenin is an extracellular matrix protein involved in the process of amelogenesis, the formation of enamel on teeth.
Kallikrein-related peptidase 4 is a protein which in humans is encoded by the KLK4 gene.
Matrix metalloproteinase-20 (MMP-20) also known as enamel metalloproteinase or enamelysin is an enzyme that in humans is encoded by the MMP20 gene.
Dentin sialophosphoprotein is a precursor protein for other proteins found in the teeth. It is produced by cells (odontoblasts) inside the teeth, and in smaller quantities by bone tissues. It is required for normal hardening (mineralisation) of teeth. During teeth development, it is broken down into three proteins such as dentin sialoprotein (DSP), dentin glycoprotein (DGP), and dentin phosphoprotein (DPP). These proteins become the major non-collagenous components of teeth. Their distribution in the collagen matrix of the forming dentin suggests these proteins play an important role in the regulation of mineral deposition. Additional evidence for this correlation is phenotypically manifested in patients with mutant forms of dentin sialophosphoprotein. Such patients suffer dental anomalies including type III dentinogenesis imperfecta.
FAM83H is a gene in humans that encodes a protein known as FAM83H. FAM83H is targeted for the nucleus and it predicted to play a role in the structural development and calcification of tooth enamel.
Amelogenesis imperfecta (AI) is a congenital disorder which presents with a rare abnormal formation of the enamel or external layer of the crown of teeth, unrelated to any systemic or generalized conditions. Enamel is composed mostly of mineral, that is formed and regulated by the proteins in it. Amelogenesis imperfecta is due to the malfunction of the proteins in the enamel as a result of abnormal enamel formation via amelogenesis.
FAM20A is a protein that in humans is encoded by the FAM20A gene.
Jalili syndrome is a genetic disorder characterized by the combination of cone-rod dystrophy of the retina and amelogenesis imperfecta. It was characterized in 1988 by Dr. I. K. Jalili and Dr. N. J. D. Smith, following the examination of 29 members of an inbred Arab family living within the Gaza Strip.
Kohlschütter-Tönz syndrome (KTS), also called amelo-cerebro-hypohidrotic syndrome, is a rare inherited syndrome characterized by epilepsy, psychomotor delay or regression, intellectual disability, and yellow teeth caused by amelogenesis imperfecta. It is a type A ectodermal dysplasia.
Tricho–dento–osseous syndrome (TDO) is a rare, systemic, autosomal dominant genetic disorder that causes defects in hair, teeth, and bones respectively. This disease is present at birth. TDO has been shown to occur in areas of close geographic proximity and within families; most recent documented cases are in Virginia, Tennessee, and North Carolina. The cause of this disease is a mutation in the DLX3 gene, which controls hair follicle differentiation and induction of bone formation. All patients with TDO have two co-existing conditions called enamel hypoplasia and taurodontism in which the abnormal growth patterns of the teeth result in severe external and internal defects. The hair defects are characterized as being rough, course, with profuse shedding. Hair is curly and kinky at infancy but later straightens. Dental defects are characterized by dark-yellow/brownish colored teeth, thin and/or possibly pitted enamel, that is malformed. The teeth can also look normal in color, but also have a physical impression of extreme fragility and thinness in appearance. Additionally, severe underbites where the top and bottom teeth fail to correctly align may be present; it is common for the affected individual to have a larger, more pronounced lower jaw and longer bones. The physical deformities that TDO causes become more noticeable with age, and emotional support for the family as well as the affected individual is frequently recommended. Adequate treatment for TDO is a team based approach, mostly involving physical therapists, dentists, and oromaxillofacial surgeons. Genetic counseling is also recommended.
Sodium/potassium/calcium exchanger 4 also known as solute carrier family 24 member 4 is a protein that in humans is encoded by the SLC24A4 gene.
Enamel-renal syndrome is a rare autosomal recessive condition. This condition is also known as idiopathic multicentric osteolysis with nephropathy. It is characterised by dental abnormalities and nephrocalcinosis.
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