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AF050: Prolamin superfamily
- Pfam domains
- PF00234: Protease inhibitor/seed storage/LTP family
Biochemical properties
The prolamin superfamily derives its name from the alcohol-soluble proline and glutamine rich storage proteins of cereals. Members of the this family are characterized by the presence of an α-helical globular domain that contains a conserved pattern of six or eight cysteine residues that form three or four intra-molecular disulfide bonds [1]. Apart from the conserved cysteine pattern, there exist litte sequence similarities between members of different subfamilies. Members of the prolamin superfamily include the cereal prolamin seed storage proteins and several families of disulfide-rich small proteins. The prolamin seed storage proteins (gliadins and glutenins) contain a repetitive coiled-coil domain rich in proline and glutamine residues and a globular disulfide-rich domain. Families of low molecular weight sulfur-rich proteins are the grain softness proteins, indolines, non-specific lipid transfer proteins, soybean hydrophobic protein, bifunctional α-amylase/protease inhibitors, and 2S albumin seed storage proteins.
Allergological significance
Several families that belong to the prolamin superfamily were described as allergens.
- Cereal prolamins: These proteins rarely account for allergic reactions. IgE reactivity to these proteins was observed in patients with wheat-induced atopic dermatitis or exercise-induced anaphylaxis [2].
- 2S albumins: The 2S albumins are a major group of seed storage proteins from a botanically diverse range of dicotyledonous plants. Many of the seed and tree nut allergens belong to the 2S albumins such as Sin a 1 from yellow mustard, Ber e 1 from Brazil nut, Jug r 1 from English walnut, and Ara h 2 and Ara h 6 from peanut [1].
- Non-specific lipid transfer proteins: nsLTPs have been suggested to mediate the transfer of phospholipids between vesicles and membranes. However, plants have used the three-dimensional scaffold of the nsLTPs in a promiscuous fashion and many nsLTPs are not able to transfer lipids. Instead, they may play a role in plant defense against fungi and bacteria. nsLTPs are found in high concentrations in epidermal tissues of fruits. Hence, they are major allergens of fruits from the Rosaceae family. In addition, allergenic nsLTPs were found in nuts, seeds, vegetables, pollen and Hevea brasiliensis latex [3, 4].
- Bifunctional α-amylase/protease inhibitors: Seeds of wheat, barley, rye, corn, and rice contain a family of inhibitors of trypsin and non-plant α-amylases. These inhibitors interfere with the digestion of plant starches and proteins by impeding insect gut enzymes. Allergens belonging this family are invloved in both respiratory and food allergies [5].
- Soybean hydrophobic protein: This protein is related to the nsLTP family and was identified as the major allergen Gly m 1 responsible for respiratory allergy to soybean hulls [6].
- Indolines: These cereal protein have anti-microbiol activities and contribute to grain softness [7]. Puroindoline from wheat was identified as an IgE binding protein [8].
- Alpha-globulins: These seed storage proteins are found in cereal grains. The wheat globulin was identified as an IgE binding protein [8].
Due to their stability to heat and gastointestinal digestion, many allergens from the prolamin superfamily are inportant food allergens and may account for severe allergic reactions [9].
References
- Mills EN, Jenkins JA, Alcocer MJ, Shewry PR.
Structural, biological, and evolutionary relationships of plant food allergens sensitizing via the gastrointestinal tract.
Crit Rev Food Sci Nutr 2004, 44, 379-407. [PubMed] - Sandiford CP, Tatham AS, Fido R, Welch JA, Jones MG, Tee RD, Shewry PR, Newman Taylor AJ.
Identification of the major water/salt insoluble wheat proteins involved in cereal hypersensitivity.
Clin Exp Allergy 1997, 27, 1120-9. [PubMed] - Pastorello EA, Robino AM.
Clinical role of lipid transfer proteins in food allergy.
Mol Nutr Food Res 2004, 48, 356-62. [PubMed] - Breiteneder H, Mills C.
Nonspecific lipid-transfer proteins in plant foods and pollens: an important allergen class.
Curr Opin Allergy Clin Immunol 2005, 5, 275-9. [PubMed] - James JM, Sixbey JP, Helm RM, Bannon GA, Burks AW.
Wheat alpha-amylase inhibitor: a second route of allergic sensitization.
J Allergy Clin Immunol 1997, 99, 239-44. [PubMed] - Gonzalez R, Varela J, Carreira J, Polo F.
Soybean hydrophobic protein and soybean hull allergy.
Lancet 1995, 346, 48-9. [PubMed] - Bhave M, Morris CF.
Molecular genetics of puroindolines and related genes: regulation of expression, membrane binding properties and applications.
Plant Mol Biol 2008, 66, 221-31. [PubMed] - Pastorello EA, Farioli L, Conti A, Pravettoni V, Bonomi S, Iametti S, Fortunato D, Scibilia J, Bindslev-Jensen C, Ballmer-Weber B, Robino AM, Ortolani C.
Wheat IgE-mediated food allergy in European patients: alpha-amylase inhibitors, lipid transfer proteins and low-molecular-weight glutenins. Allergenic molecules recognized by double-blind, placebo-controlled food challenge.
Int Arch Allergy Immunol 2007, 144, 10-22. [PubMed] - Breiteneder H, Mills EN.
Molecular properties of food allergens.
J Allergy Clin Immunol 2005, 115, 14-23. [PubMed]
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