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Impact of food matrix interaction and post-translational modifications on the allergenicity of Mal d 3, a major apple allergen

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Fruitful research on tackling food allergies

An EU-funded project has led to a better understanding of why certain proteins can cause strong allergic reactions, while at the same time providing a bright female researcher with the opportunity to resume her career.


Identifying the role and behaviour of certain proteins in triggering allergic reactions could lead to new ways of modifying allergens, new diagnostic tools and ultimately improve the lives of millions of people who suffer from food allergies. A key milestone in this effort has been the recent Marie Curie-funded CARAMEL project, which brought researchers together to focus on Mal d 3, a non-specific Lipid Transfer Protein (nsLTP) found in apples. Focus on fruit allergies ‘Millions of people live with food allergies, with reactions that range from the slightly uncomfortable to the life-threatening,’ explains CARAMEL project coordinator professor Karin Hoffmann-Sommergruber from the Medical University of Vienna. ‘For those with fruit allergies, healthy eating can be a challenge, as avoiding fruit can result in an unbalanced diet.’ For apples - the most frequently consumed fruit in Europe - four apple allergens have been officially identified, including Mal d 3. ‘Mal d 3 and its homologues from other fruits have attracted scientific interest because they can induce severe, potentially life-threatening, systemic reactions,’ explains Hoffmann-Sommergruber. 'What makes Mal d 3 (and other nsLTPs) so hazardous is that they reach the gut only slightly modified and can induce severe systemic reactions in sensitised individuals.’ The project began by isolating and purifying Mal d 3 from apple peel. In order to obtain the target protein in high quantities for further experiments, the recombinant protein was also produced in yeast. Hoffmann-Sommergruber and her team successfully demonstrated that this was an efficient way to produce large amounts of soluble and immunologically active Mal d 3. Next, the purified recombinant Mal d 3 was tested for its application as a diagnostic tool to detect specific IgE antibodies in apple allergic patients. These studies showed that the recombinant Mal d 3 displayed a high sensitivity. ‘This could allow medical professionals to differentiate patients at risk of developing severe allergic reactions (Mal d 3-sensitised) from those with a low risk of severe food allergic reactions,’ explains Hoffmann-Sommergruber. ‘This in turn will help to fine tune dietary recommendations for fruit allergic patients.’ A key project finding was that Mal d 3 interacts with certain fatty acids, and thus changes its surface exposed structure. This in turn affects its allergenicity. ‘Based on these molecular data, new strategies on how to modify certain allergens can be developed,’ says Hoffmann-Sommergruber. ‘For instance, protein variants low in allergenicity could be designed for immunotherapeutic aspects.’ Finally the interaction of Mal d 3 with pectin, an abundant component in apples, was investigated with regard to changes in protein structure and potential effects on allergenic activity. Nitration of the protein was performed and the effect on structure and stability analysed. A career boost In addition to increasing our knowledge about fruit allergies, this Marie Curie project, which funded an Intra-European Fellowship, enabled Dr Roberta Aina to resume her research career after a four-year break. ‘The programme focused on many different aspects of education and training for Dr Aina,’ says Hoffmann-Sommergruber. ‘It enabled her to acquire new scientific and technical competencies (i.e. in recombinant protein production, purification and characterisation) and develop complementary skills such as project management and supervision skills. The project has also boosted the number of active and highly trained women in science, thus decreasing the still existing gender gap in this field.’


Apple, allergy, Marie Curie, immunology, proteins, diet, fruit

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