Chrispeels comments on the Australian GM Pea Research

Comments on the Australian GM Pea Research
- Maarten J. Chrispeels, University of California San Diego,

mchrispeels.at.ucsd.edu

The recent Prescott et al paper in JFAC contains a very interesting study on the immunogenicity of amylase inhibitor in its native form (isolated from beans) and expressed as a transgene in peas. First of all, amylase inhibitor is a food protein, but also a "toxic" protein
because it inhibits our digestive amylases. This is one of the reasons you have to cook your beans! (The other toxic bean protein is phytohemagglutinin and it is much more toxic).

This particular amylase inhibitor is found in the common bean (other species have other amylase inhibitors). Even though it is a food protein, it is unlikely ever to be used for genetic engineering of human foods because it inhibits our amylases. What the results show
is that the protein, when synthesized in pea cotyledons has a different immunogenicity than when it is isolated from bean cotyledons (the native form). This is somewhat surprising but may be related to the presence of slightly different carbohydrate chains. Is there some difference in the folding or in the C-terminal processing at the two C-termini?

This amylase inhibitor is a proteolytically processed and glycosylated vacuolar glycoprotein, offering multiple steps at which processing could be different in two species and result in different epitopes. I am sure that TJ agonized over these results and the explanation may be some years in coming.

T.J. Higgins is my long-time collaborator (25 years) and I have full confidence in these studies, which, like many studies, are open to misinterpretation. The results fully support the notion that approval of every GMO should be based on an evaluation of the crop and of the
transgene.

From today in AgBioView from www.agbioworld.org : November 23, 2005
See also:
Editorial comment in Nature Biotechnology