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In vitro digestion of soluble cashew proteins and characterization of surviving IgE-reactive peptides.

SCOPE
The stability of food allergens to digestion varies. We characterized the stability of cashew allergens to digestion by pepsin and trypsin and identified IgE-binding epitopes that survive digestion.


METHODS AND RESULTS
The ability of pepsin and trypsin to digest cashew allergens was assessed with an in vitro digestion model. Samples were evaluated by SDS-PAGE, MS, ELISA, and immunoblotting to compare IgE binding. Increasing amount of protease resulted in greater degradation of higher molecular weight cashew proteins. Among cashew proteins, the 2S albumin, Ana o 3, was most resistant to digestion by both pepsin and trypsin. MS identified digestion resistant Ana o 3 protein fragments that retained reported IgE-binding epitopes. Pretreatment of extracts or purified Ana o 3 with reducing agent increased the sensitivity of Ana o 3 to protease digestion. Circular dichroism revealed the structure of purified Ana o 3 was largely alphahelical and was disrupted following reduction. Ana o 3 reduction followed by protease digestion decreased binding of serum IgE from cashew allergic patients. Our results indicate that the Ana o 3 disulfide bond dependent structure protects the protein from proteolysis.


CONCLUSION
Ana o 3 is the cashew allergen most likely to survive gastrointestinal digestion intact.