4.1—GM Proteins are tested
GM proteins are tested to insure that they are safe
Analysis of Peer-Reviewed Research:
The claims in Genetic Roulette that mis-folding of proteins added to biotech-improved plants could lead to diseases, or that mistakes in the addition of sugars to protein could lead to allergies, share two properties in common: 1) they are events that have never happened, and 2) they are highly unlikely outcomes, because researchers do many experiments to demonstrate that the protein formed in plant cells is exactly like that formed in the original organism in which the protein was found. Fortunately, cells fold and modify proteins in very similar ways and we have tools that allow us to evaluate how proteins are modified. More importantly, no adverse effect has ever been associated with the speculative claims made by several so-called experts in this section. It is fascinating how these so-called scientific experts, who all are vocal in their opposition to GM crops, can imagine horror scenarios for GM crops but cannot point to any evidence. It is worthwhile once again to point out that all GM plants, and the new proteins they contain, are carefully studied before they are approved by regulators. Ten-plus years of planting and consuming GM crops have failed to produce a single documented adverse effect.
1. The proteins present in transgenic crops are carefully evaluated before the crop is approved. Smith speculates that proteins may be modified differently in plants than they were in their original host and that this could possibly lead to the formation of potentially toxic or allergenic proteins. His assertions are not based on history, observation or evidence but are simply more unsubstantiated speculation about the potential horrors of GM crops. Developers go to great lengths to demonstrate that inserted proteins are active and that they are functionally equivalent to the original protein. As it happens, almost all organisms fold proteins the same way so that when proteins are active (and for the crop improvement to be successful the protein must be active), they are usually correctly folded (Delaney and others 2008).
2. Many proteins that are not allergens have sugars attached to them. Jeffrey Smith refers to glycosylation, which is the addition of various types of sugars to protein after they are formed in the cell. It is true that some allergens have a very specific kind of sugar addition, but it is also true that the vast majority of proteins found in plant and animal cells that have sugars added to them are not allergens (Altmann 2007). Added sugar residues on a protein itself is not evidence of allergenicity. There is not a single example in the scientific literature that shows that a bacterial protein, when glycosylated in a plant cell, has become an allergen. Thus Genetic Roulette us once again gives us science fiction and fantasy but not science fact.
3. Researchers don’t develop products that could have added sugars. Generally there is no evidence that sugar addition as such would introduce a new risk, but to provide an addtional measure of safety developers still avoid the introduction of novel proteins containing added sugars. Computer analysis of a DNA sequences can be used to predict potential sugar addition sites and proteins possessing sugar addition sites are not selected for use (Christlet, Veluraja 2001, Gavel , von Heijne G 1990, Julenius and others 2005). The protein produced in the transgenic plant is also evaluated for possible sugar addition and the construct is not used if the protein has added sugars. It is a matter of factual record that none of the transgenic crops planted in the world today expresses novel glycosylated proteins. Genetic Roulette raises the specter of new toxic proteins caused by sugar addition but is apparently unaware that there are methods to test for and to avoid such proteins.
4. The kidney bean protein that was inserted into peas resembles known plant allergens. Although researchers found that the added sugars on bean protein were different in peas than they were in beans, they provided no evidence that this was responsible for allergenicity (Prescott and others 2005). In fact, the protein from bean shares similarity with plant allergens. It may well be that the added bean allergen is denatured by cooking—beans are seldom eaten raw—and that is why it is not widely recognized as an allergen. A complication in this case is that the test system used to declare that the protein might be allergenic is not accepted by food allergists as a valid testing method (see Part 1.18) (Goodman and others 2008). Thus, no allergenicity of the controversial pea protein has been demonstrated. And no direct evidence has emerged that sugar differences caused a problem. It should be noted that many other researchers choose not to work with this bean protein because it resembled allergens and had added sugars. We think it is a good indication that scientists care about safety that this project was immediately discontinued when questions about safety arose.
5. There is no scientific evidence that GM protein mis-folding can lead to diseases. Smith claims that in moving a protein from one organism to another it may be mis-folded. In a gigantic jump of logic he notes that Mad Cow disease is caused by a mis-folding of a protein and that mis-folded GM proteins may cause prion-like diseases. As it happens, Prions, the agents that cause Mad Cow disease, are very rare proteins that have the ability to turn normal molecules of protein into mis-folded molecules of proteins. These new mis-folded proteins can then cause other molecules of the prion to also become mis-folded. Eventually all the protein ends up in the wrong form that is the cause of the disease. This baffling series of events apparently only occurs in small range of rare animal diseases, and the protein involved is absent from plants (Aguzzi and others 2008). Genetic Roulette even admits that “it is is unlikely that mis-folded proteins in current GM crops would pose such a theat.” Prion diseases cause much pain and suffering and are thus very scary to think about, but they are fortunately also exceedingly rare. No scientific evidence exists that suggests mis-folded proteins other than particular ones causing BSE type diseases can become prions. Moreover, published research shows that mis-folded proteins occur commonly in cells (Ravid, Hochstrasser 2008) making this possibility (new prions) even less likely.
6. Genetic Roulette is apparently unaware that mis-folded proteins are usually destroyed by the cell. All cells have systems for degrading mis-folded or damaged proteins (Ravid, Hochstrasser 2008). In fact, foreign proteins are often degraded when they are inserted into cells, presumably because they are recognized as non-native by the cells normal protein degradation system. The fact that prions are not degraded is one of the curious anomalies of BSE related diseases (Goldman 2007).
Aguzzi A, Baumann F and Bremer J (2008). The prion’s elusive reason for being. Annual Reviews of Neuroscience. 31:439-477.
Altmann, F. (2007) The role of protein glycosylation in allergy. Int. Arch. Allergy Immunol. 142, 99–115 (2007).
Delaney B, Astwood JD, Cunny H, Conn RE, Herouet-Guicheney C, Macintosh S, Meyer LS, Privalle L, Gao Y, Mattsson J, Levine M (2008) ILSI International Food Biotechnology Committee Task Force on Protein Safety Evaluation of protein safety in the context of agricultural biotechnology.Food Chem Toxicol. May;46 Suppl 2:S71-97.
Christlet THT, Veluraja K (2001). Database analysis of O-glycosylation sites in proteins. Biophysical Journal 80:952–960
Gavel Y, von Heijne G (1990). Sequence differences between glycosylated and non-glycosylated Asn-X-Thr/Ser acceptor sites: implications for protein engineering. Protein Eng. 3:433-442 . PROSITE documentation PDOC00001 au.expasy.org/cgi-bin/nicedoc.pl?PDOC00001 accessed Dec 23 2008
Goldberg AL (2007). On prions, proteasomes, and mad cows. N Engl J Med. 357(11):1150-2.
Goodman RE, Vieths S, Sampson HA, Hill D, Ebisawa M, Taylor SL and van Ree R (2008). Allergenicity assessment of genetically modified crops—what makes sense? Nature Biotechnology 26(1):73-81.
Julenius K, Mølgaard A, Gupta R, Brunak S. (2005). Prediction, conservation analysis and structural characterization of mammalian mucin-type O-glycosylation sites. Glycobiology, 15:153-164. NetOGlyc 3.1 Server www.cbs.dtu.dk/services/NetOGlyc/accessed Dec 23 2008.
Prescott VE, Campbell PM, Moore A, Mattes J, Rothenberg ME, Foster PS, Higgins TJ and Hogan SP (2005). Transgenic expression of bean alpha-amylase inhibitor in pea’s results in altered structure and immunogenicity. Journal of Agricultural and Food Chemistry 53(23):9023-9030. Paper from Australia’s CSIRO about discoveries which led to the discontinuation of a project to develop a genetically modified pea.
Ravid T and Hochstrasser M (2008). Review: Diversity of degradation signals in the ubiquitin-proteasome system. Nat Rev Mol Cell Biol. 9(9):679-90.
GM proteins may be mis-folded or have added molecules
- Proteins expressed in a GM plant may be processed differently than in the donor organism
- Those changes, which could include mis-folding or molecular attachments, can be harmful in unpredicted ways
- Current studies do not adequately test for these changes
A protein in a GM plant may not be identical to the same protein in the donor organism