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