Bet v I allergen is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of protein allergens.

Allergies Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermat ...

are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. Trees within the order

Fagales The Fagales are an order of flowering plants, including some of the best-known trees. The order name is derived from genus ''Fagus'', beeches. They belong among the rosid group of dicotyledons. The families and genera currently included are as ...

possess particularly potent allergens, e.g. the prototypical Bet v 1, the major white birch ('' Betula verrucosa -'' now called ''B. pendula'') pollen antigen. Bet v 1 is the main cause of type I allergies observed in early spring. Type I, or immunoglobulin E-mediated (IgE-mediated) allergies affect 1 in 5 people in Europe and North America. Commonly observed symptoms are hay fever, dermatitis, asthma and, in severe cases, anaphylactic shock. First contact with these allergens results in sensitisation; subsequent contact produces a cross-linking reaction of IgE on mast cells and concomitant release of histamine. The inevitable symptoms of an allergic reaction ensue.

Categorization

A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans. This nomenclature system is defined by a designation that is composed of the first three letters of the genus; a space; the first letter of the species name; a space and an Arabic number. In the event that two species names have identical designations, they are discriminated from one another by adding one or more letters (as necessary) to each species designation. The allergens in this family include allergens with the following designations: Bet v 1, Dau c 1, and Pru a 1. Other proteins belonging to this family include the major pollen allergens: * Aln g I from ''

Alnus glutinosa ''Alnus glutinosa'', the common alder, black alder, European alder, European black alder, or just alder, is a species of tree in the family Betulaceae, native to most of Europe, southwest Asia and northern Africa. It thrives in wet locations wh ...

'' (Alder); * Api G I from ''

Apium graveolens Celery (''Apium graveolens'') is a marshland plant in the family Apiaceae that has been cultivated as a vegetable since antiquity. Celery has a long fibrous stalk tapering into leaves. Depending on location and cultivar, either its stalks, lea ...

'' (Celery); * Car b I from '' Carpinus betulus'' (European hornbeam); * Cor a I from ''

Corylus avellana ''Corylus avellana'', the common hazel, is a species of flowering plant in the birch family Betulaceae. It is native to Europe and western Asia. It is an important component of the hedgerows that were the traditional field boundaries in lowland En ...

'' (European hazel); * Mal d I from ''

Malus domestica An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...

'' (Apple).

Structure

NMR analysis has confirmed earlier predictions of the protein structure and site of the major T-cell epitope. The Bet v 1 protein comprises 6 anti-parallel beta-strands and 3 alpha-helices. Four of the strands dominate the global fold, and 2 of the helices form a C-terminal amphipathic helical motif. This motif is believed to be the T-cell epitope. However, one very striking feature of the three-dimensional structure of Bet v 1 is the presence of a large hydrophobic cavity, which is open to the exterior and probably functions as a ligand binding site. The motif is also found in: * the wound-induced protein AoPR1 from ''

Asparagus officinalis Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial flowering plant species in the genus ''Asparagus''. Its young shoots are used as a spring vegetable. It was once classified in ...

'' (Garden asparagus); * the

pathogenesis-related protein Pathogenesis-related (PR) proteins are proteins produced in plants in the event of a pathogen attack. They are induced as part of systemic acquired resistance. Infections activate genes that produce PR proteins. Some of these proteins are antimicr ...

s from '' Phaseolus vulgaris'' (Kidney bean) and '' Petroselinum crispum'' (Parsley) (PR1-1 and PR1-3); * the disease resistance response proteins, STH-2 and STH-21, from ''

Solanum tuberosum The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United ...

'' (Potato) and pI49, pI176 and DRRG49-C from ''

Pisum sativum The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...

'' (Garden pea); * the P.sativum abscisic acid-responsive proteins ABR17 and ABR18; * and the stress-induced protein SAM22 from ''

Glycine max Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinog ...

'' (Soybean). Additionally, the core domain of Bet v 1 founds or is part of a superfamily of domains called SRPBCC ( START/RHOalphaC/ PITP/Bet v1/CoxG/CalC) that include the StAR-related lipid-transfer (START) domain.

Function

The biological function of Bet v 1 is still under investigations. Bet v 1 harbors a large hydrophobic pocket and is able to bind a large spectra of ligands in it like

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...

s and

siderophore Siderophores (Greek: "iron carrier") are small, high-affinity iron- chelating compounds that are secreted by microorganisms such as bacteria and fungi. They help the organism accumulate iron. Although a widening range of siderophore functions is n ...

s like

flavonol Flavonols are a class of flavonoids that have the 3-hydroxyflavone backbone (IUPAC name : 3-hydroxy-2-phenylchromen-4-one). Their diversity stems from the different positions of the phenolic -OH groups. They are distinct from flavanols (with " ...

s. It belongs to the pathogenesis-related (PR) proteins, which are usually expressed upon infections and stressful conditions, implicating a role in host defense. ''In vitro'', Bet v 1 has been shown to be immune-suppressive, due to its ability to bind to iron-flavonoid complexes, which it can shuttle into human monocytic cells to increase their labile iron pool and stimulate the anti-inflammatory Arylhydrocarbon receptor pathway (https://www.mdpi.com/2076-3921/12/1/42). As such, only without any ligand, Bet v 1 was able to mount a Th2-response and turned into an allergen.

References

{{InterPro content, IPR000916 Allergology Protein families