Characteristics and safety assessment of intractable proteins in genetically modified crops

Abstract

Genetically modified (GM) crops may contain newly expressed proteins that are described as "intractable". Safety assessment of these proteins may require some adaptations to the current assessment procedures. Intractable proteins are defined here as those proteins with properties that make it extremely difficult or impossible with current methods to express in heterologous systems; isolate, purify, or concentrate; quantify (due to low levels); demonstrate biological activity; or prove equivalency with plant proteins. Five classes of intractable proteins are discussed here: (1) membrane proteins, (2) signaling proteins, (3) transcription factors, (4) N-glycosylated proteins, and (5) resistance proteins (R-proteins, plant pathogen recognition proteins that activate innate immune responses). While the basic tiered weight-of-evidence approach for assessing the safety of GM crops proposed by the International Life Sciences Institute (ILSI) in 2008 is applicable to intractable proteins, new or modified methods may be required. For example, the first two steps in Tier I (hazard identification) analysis, gathering of applicable history of safe use (HOSU) information and bioinformatics analysis, do not require protein isolation. The extremely low level of expression of most intractable proteins should be taken into account while assessing safety of the intractable protein in GM crops. If Tier II (hazard characterization) analyses requiring animal feeding are judged to be necessary, alternatives to feeding high doses of pure protein may be needed. These alternatives are discussed here.

Development of Allergenicity and Toxicity Assessment Methods for Evaluating Transgenic Sugarcane Overexpressing Sucrose–Phosphate Synthase

“…Transgenic crops may contain new expressed proteins that require safety assessment procedures to evaluate protein stability [38]. Proteins with high stability in elevated temperature are generally associated with allergenic potential [3,39].…”

“…Proteins with high stability in elevated temperature are generally associated with allergenic potential [3,39]. Identification of potential protein hazards can be conducted by examining physical properties through a heating stability assessment [38]. We assume that SPS protein was susceptible to heat treatment [40].…”

Purification, characterization and safety assessment of the introduced cold shock protein B in DroughtGard™ maize

“…Therefore, it is unlikely that such fragment will pose a potential allergenic risk (Ofori-Anti et al, 2008). However, in instances where transient stability of a protein or protein fragment is observed in pepsin cleavage, sequential degradation of the fragment by pepsin followed by pancreatin has been recommended (Bushey et al, 2014;Delaney et al, 2008a). For that reason, an assessment of the susceptibility of this CSPB fragment to pancreatin was conducted.…”

“…N-glycosylation occurs in the secretory pathway and is well conserved in animals, plants, fungi, and social amoebae (Bushey et al, 2014). However, the CSPB protein is not targeted for the secretory pathway, supporting that CSPB is not N-glycosylated.…”

The Story Behind the Approval of the First Bt Maize Product

“…Examples for specific proteins are described in Raybould et al (2013), Privalle et al (2000), Hérouet et al (2005) and Madduri et al (2012). Future products may involve proteins that are more intractable, for these types of proteins slightly different approaches may be necessary (Bushey et al 2014). According to Delaney et al, the safety assessment of the protein is divided into two tiers.…”