Comparison of the α-Amylase Inhibitor-1 from Common Bean (Phaseolus vulgaris) Varieties and Transgenic Expression in Other Legumes-Post-Translational Modifications and Immunogenicity

The seeds of peas (Pisum sativum) and chickpeas (Cicer arietinum) expressing a gene for alpha-amylase inhibitor-1 (alpha AI) from the common bean (Phaseolus vulgaris) are protected from damage by old world bruchids (pea and cowpea weevils). Here, we used electrospray ionization time-of-flight mass spectrometry to compare the post-translational modifications of alpha AI from transgenic sources with the processed forms of the protein from several bean varieties. All sources showed microheterogeneity with differences in the relative abundance of particular variants due to differences in the frequency of addition of glycans, variable processing of glycans, and differences of C-terminal exopeptidase activity. The structural variation among the transgenics was generally within the range of the bean varieties. Previously, mice showed allergic reactions following ingestion of transgenic pea alpha AI but not bean alpha AI. Here, only minor differences were observed following intraperitoneal sensitization. Both of the transgenic pea and bean forms of alpha AI elicited Th1 and Th2 antibody isotype responses, suggesting that both proteins are immunogenic and could potentially be allergenic.