Gliadin

Last updated
Gliadin/LMW glutenin
Identifiers
SymbolGlia_glutenin
InterPro IPR001954
Gliadin [Seed storage proteins] N-terminal helical domain
Identifiers
SymbolGliadin
Pfam PF13016
InterPro IPR016140
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
Gliadin Gliadin.png
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.

Contents

Both gliadins and glutenins are not 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

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]

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] More specifically does the protein likely have 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 repetative sequences. These sections are likely to aggregate hydrophobicaly, liquid-liquid phase separate, potentially form β-sheets aggregates or simply entagles by its structural properties. [8] [9]

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. [ citation needed ]

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 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 Tissue transglutaminase.png
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:

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 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

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 (interstinal 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

Related Research Articles

<span class="mw-page-title-main">Gluten</span> Group of cereal grain proteins

Gluten is a structural protein naturally found in certain cereal grains. The term gluten usually refers to a wheat grain's prolamins, specifically glutelin proteins, that naturally occur in many cereal grains, and which can trigger celiac disease in some people. The types of grains that contain gluten include all species of wheat, and barley, rye, and some cultivars of oat; moreover, cross hybrids of any of these cereal grains also contain gluten, e.g. triticale. Gluten makes up 75–85% of the total protein in bread wheat.

<span class="mw-page-title-main">Coeliac disease</span> Autoimmune disorder that results in a reaction to gluten

Coeliac disease or celiac disease is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barley. Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite, and among children failure to grow normally. Non-classic symptoms are more common, especially in people older than two years. There may be mild or absent gastrointestinal symptoms, a wide number of symptoms involving any part of the body, or no obvious symptoms. Coeliac disease was first described in childhood; however, it may develop at any age. It is associated with other autoimmune diseases, such as Type 1 diabetes mellitus and Hashimoto's thyroiditis, among others.

<span class="mw-page-title-main">Gluten-free diet</span> Diet excluding proteins found in wheat, barley, and rye

A gluten-free diet (GFD) is a nutritional plan that strictly excludes gluten, which is a mixture of prolamin proteins found in wheat, as well as barley, rye, and oats. The inclusion of oats in a gluten-free diet remains controversial, and may depend on the oat cultivar and the frequent cross-contamination with other gluten-containing cereals.

Gluten exorphins are a group of opioid peptides formed during the digestion of the gluten protein. These peptides work as external regulators for gastrointestinal movement and hormonal release. The breakdown of gliadin, a polymer of wheat proteins, creates amino acids that stop the gluten epitopes from entering the immune system to activate inflammatory reactions. During this process, gluten does not fully break down, thus increasing the presence of gluten exorphins. Because of this, researchers think this is what might lead to various diseases.

Hordein is a prolamin glycoprotein, present in barley and some other cereals, together with gliadin and other glycoproteins coming under the general name of gluten. Hordeins are found in the endosperm where one of their functions is to act as a storage unit.

Prolamins are a group of plant storage proteins having a high proline amino acid content. They are found in plants, mainly in the seeds of cereal grains such as wheat (gliadin), barley (hordein), rye (secalin), corn (zein), sorghum (kafirin), and oats (avenin). They are characterised by a high glutamine and proline content, and have poor solubility in water. They solubilise best in strong alcohol (70–80%), light acid, and alkaline solutions. The prolamins of the tribe Triticeae, such as wheat gliadin, and related proteins are known to trigger coeliac disease, an autoimmune condition, in genetically predisposed individuals.

<span class="mw-page-title-main">Wheat allergy</span> Medical condition

Wheat allergy is an allergy to wheat which typically presents itself as a food allergy, but can also be a contact allergy resulting from occupational exposure. Like all allergies, wheat allergy involves immunoglobulin E and mast cell response. Typically the allergy is limited to the seed storage proteins of wheat. Some reactions are restricted to wheat proteins, while others can react across many varieties of seeds and other plant tissues. Wheat allergy is rare. Prevalence in adults was found to be 0.21% in a 2012 study in Japan.

<span class="mw-page-title-main">Triticeae glutens</span> Seed storage protein in mature wheat seeds

Gluten is the seed storage protein in mature wheat seeds. It is the sticky substance in bread wheat which allows dough to rise and retain its shape during baking. The same, or very similar, proteins are also found in related grasses within the tribe Triticeae. Seed glutens of some non-Triticeae plants have similar properties, but none can perform on a par with those of the Triticeae taxa, particularly the Triticum species. What distinguishes bread wheat from these other grass seeds is the quantity of these proteins and the level of subcomponents, with bread wheat having the highest protein content and a complex mixture of proteins derived from three grass species.

<span class="mw-page-title-main">Gluten-related disorders</span> Set of diseases caused by gluten exposure

Gluten-related disorders is the term for the diseases triggered by gluten, including celiac disease (CD), non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH) and wheat allergy. The umbrella category has also been referred to as gluten intolerance, though a multi-disciplinary physician-led study, based in part on the 2011 International Coeliac Disease Symposium, concluded that the use of this term should be avoided due to a lack of specificity.

Gluten-sensitive enteropathy–associated conditions are comorbidities or complications of gluten-related gastrointestinal distress. GSE has key symptoms typically restricted to the bowel and associated tissues; however, there are a wide variety of associated conditions. These include bowel disorders, eosinophilic gastroenteritis and increase with coeliac disease (CD) severity. With some early onset and a large percentage of late onset disease, other disorders appear prior to the coeliac diagnosis or allergic-like responses markedly increased in GSE. Many of these disorders persist on a strict gluten-free diet, and are thus independent of coeliac disease after triggering. For example, autoimmune thyroiditis is a common finding with GSE.

Anti-gliadin antibodies are produced in response to gliadin, a prolamin found in wheat. In bread wheat it is encoded by three different alleles, AA, BB, and DD. These alleles can produce slightly different gliadins, which can cause the body to produce different antibodies. Some of these antibodies can detect proteins in specific grass taxa such as Triticeae, while others react sporadically with certain species in those taxa, or over many taxonomically defined grass tribes.

Glutelins are a class of prolamin proteins found in the endosperm of certain seeds of the grass family. They constitute a major component of the protein composite collectively referred to as gluten. Glutenin is the most common glutelin, as it is found in wheat and is responsible for some of the refined baking properties in bread wheat. The glutelins of barley and rye have also been identified. Glutelins are the primary protein form of energy storage in the endosperm of rice grains.

Anti-transglutaminase antibodies (ATA) are autoantibodies against the transglutaminase protein. Detection is considered abnormal, and may indicate one of several conditions.

<span class="mw-page-title-main">HLA-DQ2</span>

HLA-DQ2 (DQ2) is a serotype group within HLA-DQ (DQ) serotyping system. The serotype is determined by the antibody recognition of β2 subset of DQ β-chains. The β-chain of DQ is encoded by HLA-DQB1 locus and DQ2 are encoded by the HLA-DQB1*02 allele group. This group currently contains two common alleles, DQB1*0201 and DQB1*0202. HLA-DQ2 and HLA-DQB1*02 are almost synonymous in meaning. DQ2 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively.

<span class="mw-page-title-main">Enteropathy-associated T-cell lymphoma</span> Complication of coeliac disease

Enteropathy-associated T-cell lymphoma (EATL), previously termed enteropathy-associated T-cell lymphoma, type I and at one time termed enteropathy-type T-cell lymphoma (ETTL), is a complication of coeliac disease in which a malignant T-cell lymphoma develops in areas of the small intestine affected by the disease's intense inflammation. While a relatively rare disease, it is the most common type of primary gastrointestinal T-cell lymphoma.

Oat sensitivity represents a sensitivity to the proteins found in oats, Avena sativa. Sensitivity to oats can manifest as a result of allergy to oat seed storage proteins either inhaled or ingested. A more complex condition affects individuals who have gluten-sensitive enteropathy in which there is an autoimmune response to avenin, the glutinous protein in oats similar to the gluten within wheat. Sensitivity to oat foods can also result from their frequent contamination by wheat, barley, or rye particles.

The immunochemistry of Triticeae glutens is important in several inflammatory diseases. It can be subdivided into innate responses, class II mediated presentation, class I mediated stimulation of killer cells, and antibody recognition. The responses to gluten proteins and polypeptide regions differs according to the type of gluten sensitivity. The response is also dependent on the genetic makeup of the human leukocyte antigen genes. In gluten sensitive enteropathy, there are four types of recognition, innate immunity, HLA-DQ, and antibody recognition of gliadin and transglutaminase. With idiopathic gluten sensitivity only antibody recognition to gliadin has been resolved. In wheat allergy, the response pathways are mediated through IgE against other wheat proteins and other forms of gliadin.

Caricain is an enzyme. This enzyme catalyses the following chemical reaction: Hydrolysis of proteins with broad specificity for peptide bonds, similar to those of papain and chymopapain

Non-celiac gluten sensitivity (NCGS) or gluten sensitivity is a controversial disorder which can cause both gastrointestinal and other problems.

The gluten challenge test is a medical test in which gluten-containing foods are consumed and (re-)occurrence of symptoms is observed afterwards to determine whether and how much a person reacts to these foods. The test may be performed in people with suspected gluten-related disorders in very specific occasions and under medical supervision, for example in people who had started a gluten-free diet without performing duodenal biopsy.

References

  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. 1 2 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. 1 2 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. 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. 1 2 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. 1 2 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. 1 2 3 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. 1 2 3 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. 1 2 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.
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