Patient-tailored cloning of allergens by phage display: Peanut (Arachis hypogaea) profilin, a food allergen derived from a rare mRNA

A peanut cDNA phage surface display library was constructed and screened fo r the presence of IgE-binding proteins. We used a serum from a peanut-sensi tized individual with a low specific IgE level to peanut extract and suffer ing from mild symptoms after peanut ingestion. A total of 10(11) cDNA clone s were screened by affinity selection towards serum IgE immobilized to soli d-phase supports. After five rounds of selective enrichment, sequence deter mination of 25 inserts derived from different clones revealed presence of a single cDNA species. The cDNA-encoded gene product, formally termed Ara h 5, shows up to 80% amino acid sequence identity to the well-known plant all ergen profilin, a 14 kD protein present only in low amount in peanut extrac ts. Immunoblot analysis of fifty sera from individuals sensitized to peanut showed that 16% had mounted a detectable IgE response to the newly identif ied peanut profilin. High-level expression as non-fusion protein in BL21 (D E3) was carried under control of the inducible T7 promoter. Peanut profilin was purified by affinity chromatography on poly-(L-proline)-Sepharose and yielded 30 mg l(-1) culture of highly pure recombinant allergen. In spite o f the high level of up to 80% amino acid identity to other plant profilins, inhibition experiments with recombinant profilins of peanut, cherry, pear, celery and birch revealed marked differences regarding their IgE-binding c apacity. (C) 2001 Elsevier Science B.V. All rights reserved.