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Microbial Bt products have been used as insecticides for morethan 40 years without documented evidence of adverse effects.Additionally, a number of toxicological studies with insecticidalCry proteins have not identified safety concerns with Bt proteins(McClintock et al., 1995; EPA, 1998). But as genetically modified(GM) crops are becoming an increasingly important feature of agriculturallandscapes. Several international organizations havedeveloped guidelines to investigate safety of foods or feeds obtainedfrom genetically modified plants to humans and livestock(WHO, 1991, 1995; OECD, 1993, 1996, 1997; FAO, 1996; FAO/WHO, 2000; ILSI, 1996).The safety of plants containing novel proteins such as theCry1Ab/Ac protein should be addressed in two complementarysteps: (1) an initial characterization and safety assessment of theprotein itself and (2) the characterization and safety evaluationof the transgenic plant. This article focuses on the first step. Thisinitial determination of the toxicological profile of the proteins isindependent of the genetic modification and can be extended toany plant variety as one element of the safety assessment of anyplant that contains and expresses the same protein. The safety ofthe Cry1Ab/Ac protein is evaluated based on an assessment of publishedinformation and on scientific studies conducted with theseproteins. The safety evaluation is consistent with several recommendationsprovided by Authorities and International Organizations
including the FAO/WHO, Codex Alimentarius and OECD.
One of the key endpoints for assessing the safety of a novel protein
is its amino acid sequence similarity with proteins that could
have potential safety concerns, i.e., known toxins or allergens. For
this reason, an amino acid sequence comparison was performed as
part of the current food safety decision tree strategy as recommended
by the FAO/WHO (2001) and the Codex Alimentarius
(2003). Immunoglobulin E (IgE) cross-reactivity between a newly
expressed protein and a known allergen should be considered a
possibility when there is more than 35% identity in a segment of
80 or more amino acids (Codex Alimentarius, 2003; FAO/WHO,
2001; Hileman et al., 2002). It is reasonable to assume that only
matches of eight contiguous and identical amino acids have some
relevance for identifying potential allergens. The recent results of
the in silico analysis showed no evidence for any similarity be-
tween the Cry1Ab/Ac protein and any known toxic or allergenic
proteins, i.e., less than 35% identity with known toxins or allergens
across a length of 80 amino acids and no continuous eight amino
acids identity with known allergens. Theoretically the Cry1Ab/Ac
protein is safe but the silico analysis had to be verified by
in vitro assays.
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