Many protein allergens are glycosylated, raising the possibility
that the glycosyl groups may contribute to their allergenicity
(Jenkins et al., 1996). This is potentially relevant when considering
the allergenicity of novel proteins for which glycosylation patterns
may differ substantially from their native counterparts. The search
for potential N-glycosylation sites found four such sites on the
Cry1Ab/Ac protein but in vitro assays proved that there was no
N-glycosylation site on the Cry1Ab/Ac protein actually.
With the exception of pollen protein, all allergenic proteins
have high stability to digestive enzymes. Therefore this stability
can be used as an indicator of the potential of a protein being an
allergen (Astwood, 1996). It has been reported that proteins that
are rapidly hydrolyzed to peptides and single amino acids smaller
than 3.5 kDa by pepsin can be considered less likely to be allergenic
(Fu et al., 2002). And if protein allergens are to reach and pass
through the intestine mucosa to elicit an allergenic response, they
must be able to resist peptic and tryptic digestion and the acid conditions
of the digestive system. The Cry1Ab/Ac protein was degraded
rapidly by digestive enzymes as assessed by both SDS–
PAGE and Western Blot. These results suggest, but do not prove,
that the protein has no allergenic activity, since the correlation between
resistance to proteolysis and allergenic activity is not absolute
(Fu et al., 2002).
The recombinant protein was used in this paper to assess the
safety of Cry1Ab/Ac protein. The result obtained from structural
and functional equivalence assay explain that the recombinant
protein produced from E. coli was an appropriate substitute for
the extracted protein directly from genetically modified rice. Heat
stability study showed the same recognition of the heat-treated
and the native proteins by anti-Cry1Ab/Ac antibodies indicated
that the conformational changes associated with denaturation
did not affect the epitope accessibility which means that the epitope
homology search, which showed no similarities with known
allergenic epitopes, has a major weight of evidence in this safety
assessment. To have a direct assessment of the protein toxicity in
mammals, an oral acute study in mice is used for evaluating the
safety of the Cry1Ab/Ac protein. In this study, the mouse acute oral
LD50 was >5000 mg kg1 (body weight), which belongs to practically
non-toxic grade. The results are coincidence with Delaney
et al. (2008) which showed the results from acute mouse toxicology
studies with proteins in GM crops were: Cry1Ab > 4000 (oral)
and Cry1Ac > 4200 (oral). These results indicated that the Cry1Ab/
Ac protein has no harm to human beings and animal.