Abstract
Ara h 1 is a major peanut allergen. Processing-induced modifications may modulate the allergenic potency of Ara h 1. Carboxymethyl lysine (CML) modifications are a commonly described nonenzymatic modification on food proteins. In the current study, we tested the ability of digestive and endolysosomal proteases to cleave CML-modified and unmodified Ara h 1 peptides. Mass spectrometric analyses of the digested peptides demonstrate that carboxymethylation of lysine residues renders these peptides refractory to trypsin digestion. We did not detect observable differences in the simulated gastric fluid or endolysosomal digestion between the parental and CML-modified peptides. One of the tested peptides contains a lysine residue previously shown to be CML modified laying in a previously mapped linear IgE epitope, but we did not observe a difference in IgE binding between the modified and parental peptides. Our findings suggest a molecular mechanism for the increased resistance of peanut allergens modified by thermal processing, such as Ara h 1, to digestion in intestinal fluid after heating and could help explain how food processing-induced modifications may lead to more potent food allergens by acting to protect intact IgE epitopes from digestion by proteases targeting lysine residues.
Highlights
Food allergies present a significant medical risk and have a negative impact on the quality of life for those affected by this condition
To characterize the effect these modifications could have during digestion, we evaluated the ability of simulated gastric fluid to digest the unmodified and Carboxymethyl lysine (CML)-modified Ara h 1 peptides in vitro
Two peptides corresponding to sites of CML-modification previously described within Ara h 1(Chassaigne et al 2007; Mattison et al 2011, 2012; Mueller et al 2013) were synthesized
Summary
Food allergies present a significant medical risk and have a negative impact on the quality of life for those affected by this condition. 10 peanut allergens have been identified to date, three of them (i.e., Ara h 1, 2, and 3) are most commonly bound by serum IgE (Koppelman et al 2004) These proteins have had their linear IgE epitopes mapped (Burks et al 1997; Stanley et al 1997; Bush et al 1998; Rabjohn et al 1999), and they have been characterized structurally Earlier reports suggested a correlation between stability to digestion and allergenicity (Astwood et al 1996), but further research has suggested the correlation is not rigid (Fu et al 2002; Thomas et al 2004; Lucas et al 2008) Some food allergens, such as 2S albumins from nuts, can cross the intestinal barrier intact and this can affect downstream antigen processing (Moreno et al 2006; Price et al 2013).
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