| Gliadin/LMW glutenin | |
|---|---|
| Identifiers | |
| Symbol | Glia_glutenin |
| InterPro | IPR001954 |
| Gliadin [Seed storage proteins] N-terminal helical domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Gliadin | ||||||||
| Pfam | PF13016 | ||||||||
| InterPro | IPR016140 | ||||||||
| |||||||||
Gliadin (a type ofprolamin) is a class ofproteins present inwheat and several othercereals within the grass genusTriticum. Gliadins, which are a component ofgluten, are essential for giving bread the ability to rise properly during baking. Gliadins andglutenins are the two main components of the gluten fraction of the wheatseed. This gluten is found in products such aswheat flour. Gluten is split about evenly between the gliadins and glutenins, although there are variations found in different sources.
Neither gliadins nor glutenins arewater-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 incoeliac (or celiac) disease. Diagnosis of this disease has recently been improving.
Gliadin can cross the intestinal epithelium.Breast milk of healthy human mothers who eatgluten-containing foods presents high levels of non-degraded gliadin.[2][3]
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]
The gliadins areintrinsically 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 theglutenins, which form extended networks of polymers due todisulphide 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 havecysteines 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 tohydrophobic interactions.[7]
Gliadins are capable to aggregate into larger oligomers and interact with other gluten proteins, due to large hydrophobic sections,poly-Q andrepetitive 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]
Gliadins areprolamins and are separated on the basis ofelectrophoretic mobility andisoelectric focusing. Gliadin peptides cross the intestinal barrier by active transport.[citation needed]
Gliadins are known for their role, along with glutenin, in the formation ofgluten. They are slightlysoluble inethanol and contain only intramoleculardisulfide links. They also cause some of the best examples of food-derivedpathogenesis. People withceliac disease (also known as gluten-sensitive enteropathy) are sensitive to α, β, and γ gliadins. Those withwheat-dependent urticaria andbaker's asthma are sensitive to ω-gliadins.[citation needed]
Gliadin can also serve as a useful delivery method for sensitiveenzymes (such assuperoxide dismutase, which is fused with gliadin to formglisodin). This helps protect them from stomach acids that cause breakdown[dubious –discuss].
For useful description of the gliadins see:
Deamidated gliadin is produced by acid or enzymatic treatment of gluten. The enzymetissue transglutaminase converts some of the abundantglutamines toglutamic 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 (or coeliac disease) is a chronic, immune-mediated intestinal disorder, in which the body becomes intolerant to gliadin, which is a component ofgluten.[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 autoimmuneenteropathy (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 ofCD4+ 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 causemalabsorption, reduced quality of life,iron deficiency,osteoporosis, an increased risk of intestinallymphomas and greater mortality.[21] It is associated with some autoimmune diseases, such asdiabetes 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 strictgluten-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]