Crystallization and preliminary X-ray analysis of the major peanut allergen Ara h 1 core region.

Peanuts contain some of the most potent food allergens known to date. Ara h 1 is one of the three major peanut allergens. As a first step towards three-dimensional structure elucidation, recombinant Ara h 1 core region was cloned, expressed in Escherichia coli and purified to homogeneity. Crystals were obtained using 0.1 M sodium citrate pH 5.6, 0.1 M NaCl, 15% PEG 400 as precipitant. The crystals diffracted to 2.25 A resolution using synchrotron radiation and belonged to the monoclinic space group C2, with unit-cell parameters a=156.521, b=88.991, c=158.971 A, beta=107.144 degrees. Data were collected at the BL-38B1 station of SPring-8 (Hyogo, Japan).

Crystal structure of the major peanut allergen Ara h 1.

Ara h 1, a 7S globulin, is one of the three major peanut allergens. We previously reported the crystallization of the core region of recombinant Ara h 1. Here, we present the crystal structure of the Ara h 1 core at a resolution of 2.43 Å. We also assayed the Ara h 1 core thermal stability and compared its final structure against other 7S globulins. The Ara h 1 core has a thermal denaturation temperature of 88.3°C and a structure that is very similar to other 7S globulins. Previously identified linear IgE epitopes were also mapped on the three-dimensional structure. Most linear epitopes were found in the extended loop domains and the coils between the N- and C-terminal modules, while others were found in the less accessible ß-sheets of the C-terminal core ß-barrel domain of each monomer. Most of these epitopes become either slightly or significantly buried upon trimer formation, implying that allergen digestion in the gut is required for these epitopes to be accessible to immunoglobulins. Our findings also suggest that both intact and partially degraded allergens should be employed in future diagnostic and immunotherapeutic strategies.