Gliadin

Gliadin (a type of prolamin) is a class of proteins present in wheat and several other cereals within the grass genus Triticum. Gliadins, which are a component of gluten, are essential for giving bread the ability to rise properly during baking. Gliadins and glutenins are the two main components of the gluten fraction of the wheat seed. This gluten is found in products such as wheat flour. Gluten is split about evenly between the gliadins and glutenins, although there are variations found in different sources.

Gliadin/LMW glutenin
Identifiers
SymbolGlia_glutenin
InterProIPR001954
Gliadin [Seed storage proteins] N-terminal helical domain
Identifiers
SymbolGliadin
PfamPF13016
InterProIPR016140
Gliadin

Gliadin is the water-insoluble component of gluten, and glutenin is water-soluble.[1] There are three main types of gliadin (α, γ, and ω), to which the body is intolerant in coeliac (or celiac) disease. Diagnosis of this disease has recently been improving.

Gliadin can cross the intestinal epithelium. Breast milk of healthy human mothers who eat gluten-containing foods presents high levels of non-degraded gliadin.[2][3]

Types

The α, γ, and ω gliadin types are separated and distinguished based on their amino acid sequences in the N-terminal cysteine domain.[4][5]

  • α-/β-gliadins – soluble in low-percentage alcohols.
  • γ-gliadins – ancestral form of cysteine-rich gliadin with only intrachain disulfide bridges[6]
  • ω-gliadins – soluble in higher percentages, 30–50% acidic acetonitrile.

Chemistry

The gliadins are intrinsically disordered proteins meaning that they have continuously altering shapes making it difficult to study them. The performed image analysis and computer simulations of the proteins show that the average shape of the gliadins follows an elliptical shape.[7] Compared to the other gluten proteins like the glutenins, which form extended networks of polymers due to disulphide bonds, are gliadins monomeric molecules in the cell, even if they in many ways are weary similar. Especially the low molecular weight glutenins are similar in the way that they have cysteines located in matching locations as many of the gliadins. However, the gliadins are unable to form polymers in the cell since its cysteines form intra-chain disulphide bonds at synthesis due to hydrophobic interactions.[7]

Biochemistry

Gliadins are prolamins and are separated on the basis of electrophoretic mobility and isoelectric focusing. Gliadin peptides cross the intestinal barrier by active transport.

Metabolism

Gliadins are known for their role, along with glutenin, in the formation of gluten. They are slightly soluble in ethanol and contain only intramolecular disulfide links. They also cause some of the best examples of food-derived pathogenesis. People with gluten-sensitive enteropathy (the severe form of which is celiac disease) are sensitive to α, β, and γ gliadins. Those with WD urticaria and Baker's asthma are sensitive to ω-gliadins.

Tissue transglutaminase

Gliadin can also serve as a useful delivery method for sensitive enzymes (such as superoxide dismutase, which is fused with gliadin to form glisodin) – this helps protect them from stomach acids that cause breakdown.

For useful description of the gliadins see:

Deamidated gliadin

Deamidated gliadin is produced by acid or enzymatic treatment of gluten. The enzyme tissue transglutaminase converts some of the abundant glutamines to glutamic acid. This is done because gliadins are soluble in alcohol and cannot be mixed with other foods (like milk) without changing the foods' qualities. Deamidated gliadin is soluble in water. The cellular immunity to deamidated α-/β-gliadin is much greater than α/β-gliadin and can result in symptomatic gluten-sensitive enteropathy.

Celiac disease
Main article: Coeliac disease

Celiac disease is a chronic, immune-mediated intestinal disorder, in which the body becomes intolerant to gliadin, which is a component of gluten.[8] Individuals with celiac disease exhibit a lifelong intolerance of wheat, barley and rye – all of which contain prolamins.[9] Gliadin proteins have the ability to provoke an autoimmune enteropathy caused by an abnormal immune response in genetically susceptible individuals. Specific amino acid sequences within the gliadin proteins are responsible for this activity.[9][10]

The main problems with this disease is that it often goes unrecognized for many years, in which it can cause serious damage to several organs,[11] and most cases currently remain unrecognized, undiagnosed and untreated. This occurs as a result of CD4+T cell recognition of deaminated gliadin polypeptide chains within the intestinal epithelium.[12][13][14][15][16] CD8+ T cells then enter the epithelium and express NK receptors specific for gliadin and transglutaminase causing intraepithelial T cells to kill enterocytes by mediating apoptosis.[12] Celiac disease with "non-classic symptoms" is the most common clinical type and occurs in older children (over 2 years old), adolescents and adults.[11] It is characterized by milder or even absent gastrointestinal symptoms and a wide spectrum of non-intestinal manifestations that can involve any organ of the body, and very frequently may be completely asymptomatic[15] both in children (at least in 43% of the cases[17]) and adults.[15] Untreated celiac disease may cause malabsorption, reduced quality of life, iron deficiency, osteoporosis, an increased risk of intestinal lymphomas and greater mortality.[18] It is associated with some autoimmune diseases, such as diabetes mellitus type 1, thyroiditis,[19] gluten ataxia, psoriasis, vitiligo, autoimmune hepatitis, dermatitis herpetiformis, primary sclerosing cholangitis, and more.[19]

The only available treatment for celiac disease is a strict gluten-free diet in which the diseased person does not ingest any gluten. There have been searches for an affordable and much better treatment, but the only treatment remains to abstain from ingesting any gluten.[11]

See also

References
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  2. Bethune MT, Khosla C (February 2008). "Parallels between pathogens and gluten peptides in celiac sprue". PLoS Pathogens. 4 (2): e34. doi:10.1371/journal.ppat.0040034. PMC 2323203. PMID 18425213.
  3. Chirdo FG, Rumbo M, Añón MC, Fossati CA (November 1998). "Presence of high levels of non-degraded gliadin in breast milk from healthy mothers". Scandinavian Journal of Gastroenterology. 33 (11): 1186–92. doi:10.1080/00365529850172557. PMID 9867098.
  4. CID 17787981 from PubChem
  5. Bromilow S, Gethings LA, Buckley M, Bromley M, Shewry PR, Langridge JI, Clare Mills EN (June 2017). "A curated gluten protein sequence database to support development of proteomics methods for determination of gluten in gluten-free foods". Journal of Proteomics. 163: 67–75. doi:10.1016/j.jprot.2017.03.026. PMC 5479479. PMID 28385663.
  6. Qi PF, Wei YM, Ouellet T, Chen Q, Tan X, Zheng YL (April 2009). "The gamma-gliadin multigene family in common wheat (Triticum aestivum) and its closely related species". BMC Genomics. 10: 168. doi:10.1186/1471-2164-10-168. PMC 2685405. PMID 19383144.
  7. Markgren J, Hedenqvist M, Rasheed F, Skepö M, Johansson E (July 2020). "Glutenin and Gliadin, a Piece in the Puzzle of their Structural Properties in the Cell Described through Monte Carlo Simulations". Biomolecules. 10 (8): 1095. doi:10.3390/biom10081095. PMID 32717949.
  8. Mowat AM (April 2003). "Coeliac disease--a meeting point for genetics, immunology, and protein chemistry". Lancet. 361 (9365): 1290–2. doi:10.1016/S0140-6736(03)12989-3. PMID 12699968. S2CID 10259661.
  9. McGough N, Cummings JH (November 2005). "Coeliac disease: a diverse clinical syndrome caused by intolerance of wheat, barley and rye". The Proceedings of the Nutrition Society. 64 (4): 434–50. doi:10.1079/pns2005461. PMID 16313685.
  10. Ciccocioppo R, Di Sabatino A, Corazza GR (June 2005). "The immune recognition of gluten in coeliac disease". Clinical and Experimental Immunology. 140 (3): 408–16. doi:10.1111/j.1365-2249.2005.02783.x. PMC 1809391. PMID 15932501.
  11. Ludvigsson JF, Card T, Ciclitira PJ, Swift GL, Nasr I, Sanders DS, Ciacci C (April 2015). "Support for patients with celiac disease: A literature review". United European Gastroenterology Journal. 3 (2): 146–59. doi:10.1177/2050640614562599. PMC 4406900. PMID 25922674.
  12. Sollid LM, Jabri B (December 2005). "Is celiac disease an autoimmune disorder?". Current Opinion in Immunology. Autoimmunity / Allergy and hypersensitivity. 17 (6): 595–600. doi:10.1016/j.coi.2005.09.015. PMID 16214317.
  13. Lundin KE, Wijmenga C (September 2015). "Coeliac disease and autoimmune disease-genetic overlap and screening". Nature Reviews. Gastroenterology & Hepatology. 12 (9): 507–15. doi:10.1038/nrgastro.2015.136. PMID 26303674. S2CID 24533103.
  14. Lionetti E, Gatti S, Pulvirenti A, Catassi C (June 2015). "Celiac disease from a global perspective". Best Practice & Research. Clinical Gastroenterology (Review). 29 (3): 365–79. doi:10.1016/j.bpg.2015.05.004. PMID 26060103.
  15. Fasano A (April 2005). "Clinical presentation of celiac disease in the pediatric population". Gastroenterology. 128 (4 Suppl 1): S68-73. doi:10.1053/j.gastro.2005.02.015. PMID 15825129.
  16. Elli L, Branchi F, Tomba C, Villalta D, Norsa L, Ferretti F, et al. (June 2015). "Diagnosis of gluten related disorders: Celiac disease, wheat allergy and non-celiac gluten sensitivity". World Journal of Gastroenterology. 21 (23): 7110–9. doi:10.3748/wjg.v21.i23.7110. PMC 4476872. PMID 26109797.
  17. Vriezinga SL, Schweizer JJ, Koning F, Mearin ML (September 2015). "Coeliac disease and gluten-related disorders in childhood". Nature Reviews. Gastroenterology & Hepatology (Review). 12 (9): 527–36. doi:10.1038/nrgastro.2015.98. PMID 26100369. S2CID 2023530.
  18. Lebwohl B, Ludvigsson JF, Green PH (October 2015). "Celiac disease and non-celiac gluten sensitivity". BMJ (Review). 351: h4347. doi:10.1136/bmj.h4347. PMC 4596973. PMID 26438584.
  19. Lundin KE, Wijmenga C (September 2015). "Coeliac disease and autoimmune disease-genetic overlap and screening". Nature Reviews. Gastroenterology & Hepatology. 12 (9): 507–15. doi:10.1038/nrgastro.2015.136. PMID 26303674. S2CID 24533103.
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