Gliadin

Protein in wheat & other cereals

Protein family

Gliadin/LMW glutenin

Identifiers
Symbol| Glia_glutenin
InterPro| IPR001954

Protein domain

Gliadin [Seed storage proteins] N-terminal helical domain

Identifiers
Symbol| Gliadin
Pfam| PF13016
InterPro| IPR016140
| Available protein structures:

Pfam  | structures / ECOD
PDB| RCSB PDB; PDBe; PDBj
PDBsum| structure summary
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.

Neither gliadins nor glutenins are water-soluble, but gliadins are soluble in 70% aqueous ethanol.[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

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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

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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] More specifically the protein likely has a tadpole-like structure with a hydrophobic core and a loose disordered tail.[8] Compared to the other gluten proteins like the glutenins, which form extended networks of polymers due to disulphide bonds, gliadins are monomeric molecules in the cell, even if they in many ways are very 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]

Gliadins are capable to aggregate into larger oligomers and interact with other gluten proteins, due to large hydrophobic sections, poly-Q and repetitive sequences. These sections are likely to aggregate hydrophobically, liquid-liquid phase separate, potentially form β-sheets aggregates or simply entangles by its structural properties.[8][9]

## Biochemistry

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

## Metabolism

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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 celiac disease (also known as gluten-sensitive enteropathy) are sensitive to α, β, and γ gliadins. Those with wheat-dependent urticaria and baker's asthma are sensitive to ω-gliadins.[citation needed]

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[dubious – discuss].

For useful description of the gliadins see:

* Triticeae glutens
* Immunochemistry of gluten

### Deamidated gliadin

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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 food's 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.[citation needed]

## Celiac disease

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Main article: Coeliac disease

Celiac disease (or coeliac disease) is a chronic, immune-mediated intestinal disorder, in which the body becomes intolerant to gliadin, which is a component of gluten.[10] Individuals with celiac disease exhibit a lifelong intolerance of wheat, barley and rye – all of which contain prolamins.[11] The main problem with this disease is that it often goes unrecognized for many years, in which case it can cause serious damage to several organs,[12] and most cases currently remain unrecognized, undiagnosed and untreated.

Gliadin proteins have the ability to provoke an autoimmune enteropathy (intestinal disease) caused by an abnormal immune response in genetically susceptible individuals. Specific amino acid sequences within the gliadin proteins are responsible for this activity.[11][13] It occurs as a result of CD4+ T cell recognition of deaminated gliadin polypeptide chains within the intestinal epithelium.[14][15][16][17][18] 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.[14]

Celiac disease with "non-classic symptoms" is the most common clinical type and occurs in older children (over 2 years old), adolescents and adults.[19] 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[17] both in children (at least in 43% of the cases[20]) and adults.[17] Untreated celiac disease may cause malabsorption, reduced quality of life, iron deficiency, osteoporosis, an increased risk of intestinal lymphomas and greater mortality.[21] It is associated with some autoimmune diseases, such as diabetes mellitus type 1, thyroiditis,[15] gluten ataxia, psoriasis, vitiligo, autoimmune hepatitis, dermatitis herpetiformis, primary sclerosing cholangitis, and more.[15]

The only available treatment for celiac disease is a strict gluten-free diet in which the affected person does not ingest any gluten-containing products. There have been searches for an affordable and much better treatment, but the only treatment remains to abstain from ingesting any gluten.[19]

## See also

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* Anti-gliadin antibodies
* Gluten immunochemistry
* Glutenin
* Non-celiac gluten sensitivity
* Gluten-related disorders
* Intestinal permeability

## References

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1. ^ Ribeiro M, Nunes-Miranda JD, Branlard G, Carrillo JM, Rodriguez-Quijano M, Igrejas G (November 2013). "One hundred years of grain omics: identifying the glutens that feed the world". Journal of Proteome Research. 12 (11): 4702–16\. doi:10.1021/pr400663t. PMID 24032428.
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. ^ a b 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. PMC 7465137. PMID 32717949.
8. ^ a b Markgren J (2022). "Aggregation of gluten proteins - from wheat seed biology to hydrogels : scientific modelling based primarily on Monte-Carlo and HPLC methods". pub.epsilon.slu.se. Archived from the original on 2022-05-16. Retrieved 2022-06-10.
9. ^ Markgren J, Rasheed F, Hedenqvist MS, Skepö M, Johansson E (2022-06-30). "Clustering and cross-linking of the wheat storage protein α-gliadin: A combined experimental and theoretical approach". International Journal of Biological Macromolecules. 211: 592–615\. doi:10.1016/j.ijbiomac.2022.05.032. ISSN 0141-8130. PMID 35577195. S2CID 248805639.
10. ^ 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.
11. ^ a b 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.
12. ^ 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.
13. ^ 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.
14. ^ a b 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.
15. ^ a b c 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.
16. ^ 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.
17. ^ a b c 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.
18. ^ 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.
19. ^ a b 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.
20. ^ 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.
21. ^ 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.

## External links

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* Gliadin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)