Cloning and Expression of 2S Albumin As a Major Allergen of Persian Walnut

Background: Food hypersensitivity to walnut usually results in mild symptoms; however, several cases of anaphylactic reactions to this product have been observed. This study aimed to determine the immunochemical characteristics of the Persian walnut and provide the recombinant form of its main allergen. Materials and Methods: The allergenic proteins of the Persian walnut were extracted by standard procedure. The IgE-binding profile was determined by common immunoassays, including ELISA and Western blotting. The characteristics of the main allergenic protein which showed a stronger and higher frequency of IgE-reactivity with the patient’s sera was identified by MALDI-TOF-TOF method. The conventional PCR was used for the amplification of the coding sequence of the target protein which was then inserted into pET-21b(+) vector and expressed in E. coli BL21. The recombinant allergen was purified by metal affinity chromatography and the ELISA and immunoblotting assays were used for the evaluation of the IgE-binding capacity of the recombinant protein. Results: All patients showed a considerable specific IgE-reactivity to total extract (OD 0.58±0.43 versus 0.047±0.026; P<0.05) in ELISA. Immunoblotting with crude extract indicated considerable IgE-reactivity of the patients’ sera with a 15-kDa allergen which was characterized as 2S albumin by mass spectrometry methods. The refolded walnut recombinant 2S albumin showed considerable IgE-reactivity in ELISA and western blotting with patients’ sera. Conclusion: We demonstrated that the refolding of walnut recombinant 2S albumin could result in the reconstruction of an IgE-reactive allergen with a rather similar immunoreactivity to its natural counterpart. The refolded recombinant protein could be a suitable candidate for diagnostic and therapeutic approaches.