471 IgE from Birch Pollen Allergic Patients Cross-reacts with Two Distinct Bet V 1 Related Proteins in Mung Beans: VIG R 1 and Cytokinin-specific Binding Protein

BACKGROUND: Mung beans (Vigna radiata) contain 2 Bet v 1 related proteins: Vig r 1, a member of the PR-10 subfamily, and cytokinin-specific binding protein (CSBP), a protein with low sequence identity (31%) to Bet v 1. We aimed to compare Vig r 1 and CSBP to Bet v 1 regarding biochemical and immunological properties. METHODS: Percent surface identity between Bet v 1, CSBP and Vig r 1 was calculated based on structural alignments using an algorithm considering backbone conformations and identities of aligned residues. The allergens were expressed in Escherichia coli and purified by metal chelate affinity and ion exchange chromatography. Secondary structures were compared using circular dichroism (CD) spectroscopy. Binding and cross-reactivity of IgE from Bet v 1-sensitized patients' sera to rCSBP, rVig r 1.0101 and rBet v 1.0101 were examined by ELISA and ELISA inhibition. RESULTS: Structural comparison of the 3 proteins revealed that 29% of the solvent-accessible surface area of CSBP was identical to Bet v 1, while Vig r 1 and Bet v 1 shared 50% surface area. In addition, 2 surface patches, conserved between Bet v 1 and CSBP, were identified as potential cross-reactive epitopes. 30% and 79% of Bet v 1-sensitized birch pollen allergic patients' sera (n = 33) showed IgE binding to CSBP and Vig r 1, respectively. Of 12 Bet v 1-sensitized patients, who reported reactions or had positive prick-to-prick tests to mung bean sprouts, 10 showed IgE binding to Vig r 1 and 7 to CSBP. Bet v 1 completely inhibited IgE binding to CSBP and Vig r 1. Furthermore, CSBP showed inhibitory activity on IgE binding to Vig r 1 and vice versa. CONCLUSIONS: This study demonstrates IgE cross-reactivity between Bet v 1 and CSBP, despite their low sequence identity. In addition to Vig r 1, a PR-10 subfamily member, IgE binding to CSBP might contribute to allergic reactions in mung bean sprouts.