Chemical modification by peroxynitrite enhances TLR4 activation of the grass pollen allergen Phl p 5

Abstract

The chemical modification of aeroallergens by reactive oxygen and nitrogen species (ROS/RNS) may contribute to the growing prevalence of respiratory allergies in industrialized countries. Post-translational modifications can alter the immunological properties of proteins, but the underlying mechanisms and effects are not well understood. In this study, we investigate the Toll-like receptor 4 (TLR4) activation of the major birch and grass pollen allergens Bet v 1 and Phl p 5, and how the physiological oxidant peroxynitrite (ONOO–) changes the TLR4 activation through protein nitration and the formation of protein dimers and higher oligomers. Of the two allergens, Bet v 1 exhibited no TLR4 activation, but we found TLR4 activation of Phl p 5, which increased after modification with ONOO– and may play a role in the sensitization against this grass pollen allergen. We attribute the TLR4 activation mainly to the two-domain structure of Phl p 5 which may promote TLR4 dimerization and activation. The enhanced TLR4 signaling of the modified allergen indicates that the ONOO–-induced modifications affect relevant protein-receptor interactions. This may lead to increased sensitization to the grass pollen allergen and thus contribute to the increasing prevalence of allergies in the Anthropocene, the present era of globally pervasive anthropogenic influence on the environment.

Protein oxidation‐induced changes in the physicochemical properties and quality of plant food

“…Studies have shown that oxidative modifications can also alter the sensitisation of plant protein. In the study of betv 4 and Phlp4, birch and grass pollen allergens, researchers found that the physiological oxidant peroxynitrite forms protein dimers and higher oligomers through protein nitration, thereby enhancing the activation of toll‐like receptor 4, resulting in increased sensitivity to grass pollen allergen (Reinmuth‐Selzle et al ., 2023). Other studies have shown that plasma could cause oxidation of sesame protein, thereby reducing the binding ability of sesame protein to IgE antibodies (Unterhauser et al ., 2023).…”

“…In addition to its nutritional value, plant-based protein is also considered as functional ingredient and playing a variety of roles in food formulations, including thickener and gelling agents, stabilisers for emulsion and foam, and adhesives for lipid and water. It has been reported that the emulsion stability of beef sausages was improved after the addition of lupin protein (dos Santos et al, 2022). Moreover, faba bean protein powders have been used to make emulsion gels including yogurt and tofu analogues, while mung bean protein, due to its good hydrophobicity and antioxidant resistance, can form an adhesive film that acts as an excellent oxygen barrier (Hadidi et al, 2022;Zheng et al, 2022b).…”

Oligomerization and tyrosine nitration enhance the allergenic potential of the birch and grass pollen allergens Bet v 1 and Phl p 5

“…However, dimer and trimer formation was observed but not quantified for the reaction of Bet v 1 with TNM ( 9 , 35 ). The reaction of Bet v 1 with ONOO yielded up to 42% protein dimers and higher oligomers ( 63 ). For Bet v 1, the tyrosine residues, Y5, Y66 and Y150 were suggested to be involved in the dityrosine cross-linking due to their solvent-exposed position ( 35 , 64 ).…”

“…For Phl p 5, exposure to O /NO and ONOO lead to the formation of protein dimers and higher oligomers for up to 50% of the protein mass ( 30 , 63 ). For dimerization and further oligomerization, the effect of steric hindrance, however, is likely more important than for the nitration reaction ( 22 ).…”

“…For example, for the reaction with TNM, the ND of Bet v 1 strongly depends on the molar ratio of TNM to tyrosine residues ( 29 ), whereas the reaction time seems to be less important ( 51 ). Similarly, also for the reaction with ONOO , the ND depends on the molar ratio of ONOO to tyrosine residues ( 29 , 30 , 63 ). In contrast to the reaction with TNM, the ND for the reaction of Bet v 1 with ONOO depends on the reaction time.…”