Phenylcoumaran benzylic ether and isoflavonoid reductases are a new class of cross‐reactive allergens in birch pollen, fruits and vegetables

Abstract

We investigated the biochemical function of the birch pollen allergen Bet v 6 and its role in the IgE‐cross‐reactivity between birch pollen and plant foods, and characterized Pyr c 5, a Bet v 6‐related food allergen, from pear; the proteins were expressed as His‐Tag fusion proteins in Eschershia coli and purified by Ni‐chelate affinity chromatography under native conditions. Nonfusion proteins were obtained by factor Xa protease treatment. The highest degree of amino‐acid sequence identity of Pyr c 5 and Bet v 6 was found with a plant protein related to a defense mechanism, which we have named phenylcoumaran benzylic ether reductase (PCBER) based on its ability to catalyze the NADPH‐dependent reduction of 8–5′ linked lignans such as dehydrodiconiferyl alcohol to give isodihydrodehydrodiconiferyl alcohol. Enzymatic assays with recombinant Pyr c 5 and Bet v 6 showed PCBER catalytic activity for both recombinant allergens. Both Pyr c 5 and Bet v 6 allergens had similar IgE binding characteristics in immunoblotting and enzyme allergosorbent tests (EAST), and bound IgE from 10 sera of birch‐pollen‐allergic patients including six pear‐allergic subjects. EAST inhibition experiments with Pyr c 5 as the solid phase antigen suggested that homologous allergens may be present in many vegetable foods such as apple, peach, orange, lychee fruit, strawberry, persimmon, zucchini (courgette), and carrot. In extracts of pear, apple, orange, and persimmon, the presence of proteins of approximately 30–35 kDa containing Bet v 6 cross‐reactive epitopes was demonstrated with two Bet v 6‐specific monoclonal antibodies. Recombinant Pyr c 5 triggered a strong, dose‐dependent mediator release from basophils of a pear‐allergic subject, suggesting that Pyr c 5 has the potential to elicit type I allergic reactions.

Crystal Structures of Pinoresinol-Lariciresinol and Phenylcoumaran Benzylic Ether Reductases and Their Relationship to Isoflavone Reductases

“…For this reason, PCBER was proposed to be the likely progenitor of PLR and IFR because it catalyzes the more general conversion, and the other two enzymes catalyze the more specific conversions (4). Furthermore, from a physiological perspective, both PCBERs and IFRs have been identified as minor allergens in various fruits and vegetables (28); the regions on the proteins that confer these allergenic responses are, however, unknown. Despite the importance of the lignans and isoflavonoids in plant biology, in human health, and in industries that use heartwoods as their main resource, systematic studies on the enzymes involved have not been done.…”

Comparative analyses of transcriptome and proteome in response to cotton bollworm between a resistant wild soybean and a susceptible soybean cultivar

“…Glyma06g03410 encoded a putative phenylcoumaran benzylic ether reductase (PCBER), an enzyme responsible for the synthesis of lignans in the phenylpropanoid pathway (Karamloo et al 2001;Nuoendagula et al 2016;Vander et al 2000). The expression of Glyma06g03410 were up-regulated by 3.0 fold change in response to H. armigera in ED059 while down-regulated by 3.0 fold change in cv.…”

Molecular Properties of Plant Food Allergens: A Current Classification into Protein Families

“…Allergens from this family include the minor birch pollen allergen Bet v 6, which has been demonstrated to cross-react with IFR from pear (Pyr c 5), lichee, and sharon fruit [54,55]. Additionally, Bet v 6-specific serum IgE recognized bands at the corresponding size in apple mango, banana, and carrot extracts [56].…”