Biology:Ara h1

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Ara h 1
Ara h 1 structure.jpg
Identifiers
OrganismArachis hypogaea (peanut)
Symbolara h 1
UniProtE5G076

Ara h 1 is a seed storage protein from Arachis hypogaea (peanuts). It is a heat stable 7S vicilin-like globulin[1] with a stable trimeric form[2] that comprises 12-16% of the total protein in peanut extracts.[3] Ara h 1 is known because sensitization to it was found in 95% of peanut-allergic patients from North America. In spite of this high percentage, peanut-allergic patients of European populations have fewer sensitizations to Ara h 1.[4]

Structure

Ara h 1 is a vicilin, located in the protein fraction of the peanut cotyledon.[5][6] Ara h 1 forms homotrimers, and due to its highly stable structure, mediated through hydrophobic interactions, it has been established as an allergen.[7]

Hydrophobic residues on α-helical bundles are located on the ends of each trimer monomer. Ara h 1 presents an overall pleat like bicupins, N- and C-terminal domains are superposed in 1.9 Å. The molecule has two modules related by an axis perpendicular to the three pleat axes of the trimer. They interact through their hydrophobic parts. The trimeric assemblies are stabilized by multiple hydrogen bonds.

Influence of Ara h 1 in peanut allergies

The protein Ara h 1 plays an important role in peanut allergic reactions. Several studies have demonstrated that the protein fraction of the cotyledon is the allergenic portion of the peanut.[5][8] Ara h 1 makes up 12% to 16% of the total protein in peanut extracts and is classified as a major peanut allergen because it provokes sensitization in 35% to 95% of patients with this allergy.[3]

This protein is a very potent allergen and it causes a severe reaction. The symptoms can be:

  • Skin reaction: urticarial, redness or edema.
  • Itchy reaction: usually around the mouth and throat.
  • Digestive problems: such as diarrhea, stomach cramps, nausea or vomiting.
  • Breath problems: it has a relation with the inflammation reaction which causes the blockage of the air passages.
  • Heart problems: histamine can cause a coronary artery spasm.
  • Anaphylaxis: a whole-body allergic reaction that causes low blood pressure, suffocation and can bring a person to death.

As it has been shown that saliva contains up to 1110 mg/ml of Ara h 1 the exposure to peanut through saliva may cause local and systematic allergic reactions.[9] So it's important to be careful and advised in terms of sharing utensils and kissing.

Another aspect to take into account too is that cooking methods can affect the allergenicity of peanut. For instance, roasted peanuts have higher levels of Ara h1 than fried and boiled peanut preparations.[10] When it comes to roasting peanuts, it increases the efficiency of Ara h1 extraction and/or the accessibility of the epitopes recognized by the antibodies used to measure the allergen.[11]

Treatment and Studies

No treatment is currently available, avoidance is the only option for peanut-allergic individuals. Unfortunately, consumers can be inadvertently exposed to peanut allergens when food becomes contaminated from processing lines shared with other peanut products. Therefore, there can be labelling mistakes because companies may not include peanuts as ingredients.

In consequence, therapeutic interventions and/or hypoallergenic peanuts are needed to prevent anaphylactic reactions caused by accidental ingestion of peanut-containing products by allergic individuals.

Several tests for peanut have been developed using polyclonal antibodies raised either against peanut extracts or against the peanut protein conarachin A. With that kind of test it can only be measured the total peanut components or proteins, or antigens such as conarachin A, but do not measure specific peanut allergens.[12] [13] [14] [15] [16] Commercial assays express peanut components in parts per million (ppm) by comparison with a standard extract. This make the results difficult to standardize and these tests do not provide quantitative measurements of actual allergen exposure. In these tests, peanut allergens are measured in foods by immunoassay with human IgE antibodies.[17]

In 2003 a monoclonal antibody-based enzyme immunoassay (ELISA) was developed to monitor the major peanut allergen, Ara h 1. Unlike other assays, this test provides quantitative measurements of allergen levels in food products in absolute units.[2]

References

  1. ↑ "The major peanut allergen Ara h 1 and its cleaved-off N-terminal peptide; possible implications for peanut allergen detection". Journal of Agricultural and Food Chemistry 52 (15): 4903–7. July 2004. doi:10.1021/jf049697o. PMID 15264933. 
  2. ↑ 2.0 2.1 "Monitoring peanut allergen in food products by measuring Ara h 1". The Journal of Allergy and Clinical Immunology 111 (3): 640–5. March 2003. doi:10.1067/mai.2003.118. PMID 12642850. 
  3. ↑ 3.0 3.1 "Identification and partial characterization of multiple major allergens in peanut proteins". Clinical and Experimental Allergy 28 (6): 743–51. June 1998. doi:10.1046/j.1365-2222.1998.00301.x. PMID 9677140. 
  4. ↑ "The many faces of the peanut". Allergy Proceedings 10 (4): 291–4. 1989. doi:10.2500/108854189778959957. PMID 2676719. 
  5. ↑ 5.0 5.1 "Peanut sensitivity". Allergy Proceedings 10 (4): 261–4. 1989. doi:10.2500/108854189778959975. PMID 2676716. 
  6. ↑ "Peanut oil is not allergenic to peanut-sensitive individuals". The Journal of Allergy and Clinical Immunology 68 (5): 372–5. November 1981. doi:10.1016/0091-6749(81)90135-4. PMID 7299001. 
  7. ↑ "Biochemical and structural analysis of the IgE binding sites on ara h1, an abundant and highly allergenic peanut protein". The Journal of Biological Chemistry 273 (22): 13753–9. May 1998. doi:10.1074/jbc.273.22.13753. PMID 9593717. 
  8. ↑ "Detection of allergy to nuts by the radioallergosorbent test". The Journal of Allergy and Clinical Immunology 57 (4): 302–9. April 1976. doi:10.1016/0091-6749(76)90086-5. PMID 1262606. 
  9. ↑ "The major glycoprotein allergen from Arachis hypogaea, Ara h 1, is a ligand of dendritic cell-specific ICAM-grabbing nonintegrin and acts as a Th2 adjuvant in vitro". Journal of Immunology 177 (6): 3677–85. September 2006. doi:10.4049/jimmunol.177.6.3677. PMID 16951327. 
  10. ↑ "Effects of cooking methods on peanut allergenicity". The Journal of Allergy and Clinical Immunology 107 (6): 1077–81. June 2001. doi:10.1067/mai.2001.115480. PMID 11398088. 
  11. ↑ "Quantification of Ara h 1 in peanuts: why roasting makes a difference". Clinical and Experimental Allergy 36 (6): 824–30. June 2006. doi:10.1111/j.1365-2222.2006.02490.x. PMID 16776684. 
  12. ↑ Hefle, Susan L.; Bush, Robert K.; Yunginger, John W.; Chu, Fun Sun (1994). "A sandwich enzyme-linked-immunosorbent-assay (ELISA) for the quantitation of selected peanut proteins in foods". J. Food Prot. 5: 419-423. 
  13. ↑ "Indirect competitive ELISA for determination of traces of peanut (Arachis hypogaea L.) protein in complex food matrices". Journal of Agricultural and Food Chemistry 47 (2): 603–11. February 1999. doi:10.1021/jf980775f. PMID 10563939. 
  14. ↑ "A comparison of commercially available peanut ELISA test kits on the analysis of samples of dark and milk chocolate". Journal of Immunoassay & Immunochemistry 23 (4): 451–9. 2002. doi:10.1081/ias-120015476. PMID 12458728. 
  15. ↑ Mills, E.N.C.; Potts, A.; Plumb, G.W.; Lambert, N.; Morgan, M.R.A. (1997). "Development of a rapid dipstick immunoassay for the detection of peanut contamination of food". Food Agric. Immunol. 9: 37–50. doi:10.1080/09540109709354932. 
  16. ↑ "Enzyme immunoassay for determination of peanut proteins in food products". Journal of AOAC International 79 (6): 1411–6. 1996. PMID 8946719. 
  17. ↑ "Immunoassay of peanut allergens in food-processing materials and finished foods". The Journal of Allergy and Clinical Immunology 86 (1): 41–4. July 1990. doi:10.1016/s0091-6749(05)80121-6. PMID 2370388. 




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