Identification of a thermal processing-induced modification site on the Ana o 3 cashew allergen

Authors: Mattison, Chris; Grimm, Casey; LI, YICHEN - Oak Ridge Institute For Science And Education (ORISE); CHIAL, HEIDI - Biomed Bridge; MCCASLIN, DARRELL - University Of Wisconsin; Chung, Si Yin; BREN-MATTISION, YVETTE - Biomed Bridge; RICHARD, WASSERMAN - Allergy Partners Of North Texas Research

Submitted to: American Chemical Society
Publication Type: Abstract Only
Publication Acceptance Date: 9/28/2016
Publication Date: 11/13/2016
Citation: Mattison, C.P., Grimm, C.C., Li, Y., Chial, H.J., Mccaslin, D.R., Chung, S., Bren-Mattision, Y., Richard, W.L. 2016. Identification of a thermal processing-induced modification site on the Ana o 3 cashew allergen. American Chemical Society. https://scsb.utmb.edu/swrm-2016/SWRM_2016_Final_Technical_Program.pdf.

Interpretive Summary: Cashew nuts are a common cause of food allergy and reactions to cashew nuts can be severe. Cooking can alter the properties of food allergens and reduce or enhance their ability to cause allergic reactions. Cashew nuts have three identified allergens including Ana o 1, Ana o 2, and Ana o 3. We show that heating cashew nuts can alter the solubility of cashew nut allergens, in particular the Ana o 3 allergen. Heating cashew nuts can increase the relative proportion of Ana o 3 released in soluble cashew nut extracts. We also identify for the first time a specific amino acid in the Ana o 3 cashew allergen that can be modified during heating. Mass-spectrometric analysis identified two independent modifications on the Arginine-111 residue of Ana o 3 from roasted but not raw cashew nut extracts. This residue lies within a previously mapped IgE epitope, but we do not see any change in IgE binding using six independent sera from cashew allergic patients. Our analysis also indicated that Ana o 3 purified from raw and roasted cashew nuts had similar structure and particle size. The stability of Ana o 3 purified from raw and roasted cashew nuts to trypsin digestion was also similar. Continued research on this Ana o 3 modification and similar in situ heating-induced allergen modifications, combined with clinical testing, will clarify the role of thermal processing in food allergy.

Technical Abstract: Cashew nuts are a common cause of food allergy and reactions to cashew nuts can be severe. Thermal processing can alter the properties of food allergens including their structure, solubility, and cause non-enzymatic reactions between reactive sugar carbonyl groups and amino groups within proteins. We show that heating cashew nuts can alter the solubility of seed storage proteins that have been shown to cause allergy to cashew nuts, and identify and characterize heating induced modifications in the Ana o 3 cashew allergen. Mass-spectrometric analysis of raw and roasted cashew nut extracts identified two independent modifications on the Arginine-111 residue of Ana o 3 from roasted but not raw cashew nuts. The mass changes we observed are consistent with formation of carboxyethyl and hydroimidazolone modifications at the Arginine-111 residue, and we observed these same modifications in Ana o 3 purified from roasted cashew nuts. Circular dichroism indicated that Ana o 3 purified from raw and roasted cashew nuts had similar secondary structure, and dynamic light scattering analysis indicated there was no observable difference in Ana o 3 particle size. The stability of Ana o 3 purified from raw and roasted cashew nuts to in vitro trypsin digestion was similar. We did not observe differences in IgE binding to Ana o 3 by ELISA among a cohort of cashew allergic patient sera demonstrated to recognize Ana o 3 by immunoblot. We have identified for the first time a heating-induced modification formed in situ on the cashew nut allergen Ana o 3. Continued research on similar in situ heating-induced allergen modifications, combined with clinical testing, will clarify the role of thermal processing in food allergy.