Cloning, expression, and purification of recombinant major mango allergen Man i 1 in Escherichia coli

In recent years, the number of people around the world who suffer from fruit allergies has increased. Mango can induce anaphylaxis, and two major mango allergens have been identified - Man i 1 and Man i 2. Apart from their molecular weights and pI values, no other information about them is known. This work identifies the DNA and amino acid sequences of Man i 1 and constructs an expression system for recombinant Man i 1 (rMan i 1). Firstly, 3' and 5' RACE assays were used to identify the cDNA fragment of Man i 1. Subsequently, the full length of Man i 1 cDNA was inserted into a pET-21a(+) vector, and the inserted plasmid was transformed to Escherichia coli BL21 (DE3) to express rMan i 1. The conditions for the expression of rMan i 1, including IPTG concentration, induction temperature, and induction time, were optimized. The highest amount of soluble rMan i 1 was obtained after induction with 0.1 mM IPTG at 16 °C for 20 h. The His-tagged rMan i 1 was purified using Ni-NTA agarose and its identity was verified using an anti-histidine antibody and the serum of a mango-allergic person. Additionally, rMan i 1 was identified as glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and shared 86.2% identity in amino acid sequence of GAPDH from wheat. Finally, an E. coli expression system of rMan i 1 was established, with the potential to be used in immunotherapy against mango allergy or the development of assays for detecting the residues of mango allergens.