Bt Brinjal The scope and adequacy of the GEAC environmental risk assessment

18 Bt Brinjal: The GEAC environmental risk assessmentTransgene ExpressionFinding 9. The description of Ccry1A is inadequate for supporting risk assessment. Expression level of Ccry1A isneeded in pollen of Bt brinjal EE-1. There is no need to use a protein not identical to Ccry1A in any the experimentsused to support risk assessment. The expression level of the marker genes is assumed to be low. This should bedemonstrated empirically.Amino acid sequence of toxinThe Bt toxin gene is intended to be aBOX 2chimeric protein of cry1Ac and cry1Ab.Surrogate ProteinsNo data are provided that describedefinitively the protein(s) that is(are) A surrogate protein is one that is substituted for the actual protein. “Surrogate”actually expressed in EE-1. Consequently has at least two possible meanings in the present context.the expressed protein is not fully known, Most commonly, a surrogate protein is one that is produced from awhich is unacceptable for developing surrogate expression system, often Escherichia coli. This is also calleda risk assessment. What is known is heterologous production of the protein. In this meaning, the surrogate proteinthat it has a molecular weight that is has the same amino acid sequence as the actual protein, but it is producedapproximately as expected and it reacts to in a different way. Such proteins may be different from the actual protein ifcertain antibodies the same as Cry1Ac. the actual protein is modified post-translationally in the plant. HeterologousIn the rest of this document, the protein systems are not able to replicate post-translational modification, and as awill be referred to as Ccry1A (a chimeric consequence it is possible for there to be structural and functional differencesCry1A, probably closely related to between the actual protein and the one that is produced heterologously.Cry1Ac), the product of the ccry1A gene. A second and more problematic meaning of the term “surrogate” is aprotein that does not have the identical primary amino acid sequence. ThisUse of surrogate proteinsis more problematic because differences in amino acid sequence are knownSurrogate Cry1Ac protein (Box 2) is to affect the structural and functional properties of proteins. In other wordsused for some of the environmental risk differences should be expected unless proven otherwise. To say otherwise is aassessment tests. There is not an adequate bit like saying that cow’s milk is the same as goat’s milk in the hope that peoplebiological justification for accepting this will be believe it because they had never tasted both of them.choice, and GEAC does not adequately Typically, the justification for using surrogate proteins is that they areconsider the problems involved with it. significantly less expensive to acquire than the actual protein. HeterologousAll of the toxicological experiments production is often much less expensive than isolation and purification of aperformed in the laboratory that are protein from living plants. However, production of a protein with identicalreported in EC-II, the Dossier and the amino acid structure as the actual protein is not that much more expensiveSupplemental Materials relied on a than creating a protein that is merely similar, but not identical. Thus there aresurrogate Cry1Ac protein. The surrogate economic reasons to rely on heterologous proteins in risk assessment, exceptprotein is surrogate in both the sense when assessing the most important risks. However, there is little justificationthat it is produced heterologously in a for using similar but not identical proteins in any risk assessment test.genetically engineered E. coli bacterium The surrogate Cry1Ac toxin used in several of the environmental riskand because it does not have the identical assessment experiments is surrogate in both senses of the term. Biologically,amino acid sequence as EE-1 is expected each of these extrapolations due to surrogacy requires some scientific data andto have (Box 2).justification that the extrapolation is valid for the purpose of risk assessment.In the present case, because the aminoacid sequence of the Ccry1A toxin in EE-1 is not actually known, it is not really possible to know how similar the surrogatetoxin is to it. This deficiency must be addressed before it is possible to interpret accurately the results of the toxicologicalexperiments.