…. and others who must deal with allergies to peanuts. A commodity that would be of considerable utility and value, a hypoallergenic peanut, is the goal of several laboratories. One group, consisting of labs at a USDA research unit in New Orleans and the campus of the University of Georgia in Tifton, recently published an interesting and promising approach to develop such a commodity. These researchers set out to screen wild relatives of the peanut (Arachis hypogaea L.) for variants of the principle allergen in peanuts, the seed storage protein Ara h 2.01, that did not possess the allergenic properties of the peanut protein. They used an approach called EcoTILLING (1) to screen several accessions of the wild relative Arachis duranensis for those with point mutations in the gene homologous to that encoding Ara h 2.01. In so doing, they identified several such variants, including one that had a significant reduction in IgE binding but otherwise seemed to cause a minimal structural change in the protein. This result is encouraging, as it may provide a way to replace, by standard breeding or by TILLING-assisted mutagenesis, the offending seed storage protein with one that is less allergenic.
The abstract of the study by Ramos et al:
Peanut (Arachis hypogaea L.), can elicit type I allergy becoming the most common cause of fatal food-induced anaphylactic reactions. Strict avoidance is the only effective means of dealing with this allergy. Ara h 2, a peanut seed storage protein, has been identified as the most potent peanut allergen and is recognized by approximately 90% of peanut hypersensitive individuals in the US. Because peanut has limited genetic variation, wild relatives are a good source of genetic diversity. After screening 30 Arachis duranensis accessions by EcoTILLing, we characterized five different missense mutations in ara d 2.01. None of these polymorphisms induced major conformational modifications. Nevertheless, a polymorphism in the immunodominant epitope #7 (S73T) showed a 56–99% reduction in IgE-binding activity and did not affect T cell epitopes, which must be retained for effective immunotherapy. The identification of natural hypoallergenic isoforms positively contributes to future immunological and therapeutic studies and peanut cultivar development.
The citation: Ramos ML, Huntley JJ, Maleki SJ, Ozias-Akins P. 2008. Identification and characterization of a hypoallergenic ortholog of Ara h 2.0. Plant Mol. Biol., in press (published on line on Nov. 14; doi 10.1007/s11103-008-9428-z)
(1) EcoTILLING is an adaptation of the process known as TILLING to identify polymorphisms, usually single nucleotide changes, in wild populations. Briefly, DNA segments that correspond to genes of interest are amplified by PCR, the products denatured and then reannealed, and then treated or analyzed in ways so as to identify polymorphisms. For example, the approach described in the linked article uses an enzyme that digests single-stranded DNA; this yields small DNA fragments that can be easily identified.