Allergen homologues, pathogenesis-related 1, polygalacturonase, and pectin methyl esterase from Japanese hop

Background: Japanese hop is an important cause of weed pollinosis in East Asia. Its pollen is abundant in autumn. This pollen is known to be the cause of many allergic diseases. However, molecular characteristics of its allergens have not been elucidated.

Objective: In this study, we produced recombinant proteins of allergen homologues from Japanese hop by the analysis of expressed sequence tags (EST), and evaluated its allergenicity.

Methods: cDNA library was constructed using as little as 50 ng of total RNA from Japanese hop pollen. Allergen homologues were identified by the initial screening of 963 EST clones. Recombinant proteins were overexpressed in the E. coli expression system and purified using Ni-nitrilotriacetic acid-agarose. Purified proteins were analyzed by ELISA.

Results: Japanese hop pathogenesis-related 1 protein (PR-1) shares 37.0 to 44.4% of amino acid sequence identity with Art v 2, Cuc m 3, and Cyn d 24. Pectin methyl esterase (PME) shows 23.2 to 50.2% of identities to Act d 7, Ole e 11, and Sal k 1. Polygalacturonase (PGs) shows 16.7 to 19.3% of identities to Phl p 13, Cry j 2, Cha o 2, Jun a 2, Pla a 2, and Pla or 2. IgE antibodies from Japanese hop allergy patients' sera recognized PR-1 (3.4%), PME (13.8%), PGs (3.7%), and profilin (13.8%), respectively.

Conclusion: Novel allergenic components were identified, even though low IgE reactivity was displayed reflecting the low degree of cross-reactivity with other pollen allergens. We believe that these molecules have worth further studies.

Keywords: Japanese hop; Pathogenesis-related 1; allergic diseases; pectin methyl esterase; pollinosis; polygalacturonase.