For immediate release
11 January 2005

The shape of allergy - what makes an allergen an allergen

An enduring mystery for allergy researchers has been the unpredictable distribution of allergens in plants. For example, being allergic to birch pollen can predispose a person to allergy from distantly related plant foods such as celery, apple or soy.

Most allergens are proteins. Research published on Tuesday identifies 129 plant allergens in just four main protein families.

“Knowing what makes a protein more likely to become an allergen could make it easier for manufacturers to identify potential allergens in novel foods and ingredients, preventing them from reaching the consumer”, said Dr Clare Mills, head of the allergy research team at the UK’s Institute of Food Research.

Proteins are constructed from amino acids, and previous research has focused on analysing the sequence of amino acids to identify potential allergens. However, this can lead to false predictions. Sequence data alone does not reveal how amino acids interact to construct proteins.

A video clip (AVI format 3.5Mb) shows how we can predict that red and pink regions might bind an IgE antibody but cyan should not.

The interaction of amino acids creates proteins folded into particular shapes. The new research by a team of scientists considered both amino acid sequence and structural similarities between surface features of plant proteins using a 3D computer model.

“By modelling surface features of proteins from a range of flowering plants, we were able to explain why cross-reactions can occur between species that otherwise seem dissimilar”, said Dr Mills. “This is especially important to help us understand why people with allergy to birch pollen can suffer related allergies to fresh fruits and vegetables”.

Flowering plants first appeared over 100 million years ago during the late Jurassic period, the age of the dinosaurs. Flowering plants became the most dominant plant on Earth and today include all our food plants. Very early in their evolution there was a split into two major groups. Some plant protein structures changed and some stayed the same or were ‘conserved’.

“We found that even a single conserved region on the surface structure of a protein can cause cross-reactivity”, said Dr Heimo Breiteneder of the Medical University of Vienna.

Scientists had already observed that although humans consume an enormous diversity of plant foods, just a few foods account for the majority of food allergies. However, their relatedness remained unclear. For the first time, the distribution of plant food allergens has been measured according to protein families. The scientists found that 129 allergens could be classified into just 20 out of 3849 possible protein families, with just four ‘superfamilies’ accounting for more than 65% of food allergens.

“We are only now in a position to begin to understand what makes an allergen an allergen”, said Dr Breiteneder.

The research, published in the Journal of Allergy and Clinical Immunology, was funded through the Biotechnology and Biological Sciences Research Council (BBSRC) competitive strategic grant to IFR and Rothamsted Research with additional support from the EU. The research is featured as “The Editor’s Choice” in the journal. Breiteneder and Mills have published a review of the molecular properties of food allergens in the same issue.

Notes to Editors

• Please contact Zoe Dunford for more information, images or animations of proteins, and an interview with Dr Clare Mills: 01603 255111 / 07768 164185 zoe.dunford@ifr.ac.uk
  
• “Structural relatedness of plant food allergens with specific reference to cross-reactive allergens: An in silico analysis”, John A. Jenkins, Sam Griffiths-Jones, Peter R. Shewry, Heimo Breiteneder and E.N. Clare Mills. Journal of Allergy and Clinical Immunology
  
• Animation by American Academy of Allergy, Asthma and Immunology (AAAAI)
  
• The mission of the Institute of Food Research (www.ifr.ac.uk) is to carry out independent basic, and strategic research on food safety, quality, nutrition and health. It is a company limited by guarantee, with charitable status, grant aided by the Biotechnology and Biological Sciences Research Council (BBSRC)
  
• The Medical University of Vienna (www.meduniwien.ac.at) was established as an independent Austrian University in January 2004. With more than 5000 employees and approximately 10.000 students, the Medical University of Vienna is one of the great medical academic institutions in Europe founded 1365 as the former Medical Faculty of the University of Vienna
  
• Dr Sam Griffiths-Jones is from the Wellcome Trust Sanger Institute. Formerly the Sanger Centre, the Wellcome Trust Sanger Institute was founded in 1993 by the Wellcome Trust and the UK Medical Research Council (MRC). The Wellcome Trust Sanger Institute is a non-trading, non-profit making registered charity involved in biomedical research
  
• Professor Peter Shewry is from Rothamsted Research, (www.rothamsted.ac.uk). The mission of Rothamsted Research is to be a world leading scientific research establishment making significant contributions, nationally and internationally to the sustainable management of agricultural land and the environment through innovations that lead to sustainable products and practices reducing reliance on non-renewable inputs.

What next?

• To understand the allergens responsible for peanut allergy. For example, whilst peanuts are a major allergen, their close botanical brothers peas pose little threat. And although peanuts and tree nuts are not related (peanuts are classified as legumes), cross-reactions occur. This remains a mystery, and is under investigation at IFR.

 

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