Assessment of Natural Variability of Maize Lipid Transfer Protein Using a Validated Sandwich ELISA

Immunoassays and Mass Spectrometry for Determination of Protein Concentrations in Genetically Modified Crops

Quantifying protein levels in genetically modified (GM) crops is crucial in every phase of development, deregulation, and seed production. Immunoassays, particularly enzyme-linked immunosorbent assay, have been the primary protein quantitation techniques for decades within the industry due to their efficiency, adaptability, and credibility. Newer immunoassay technologies like Meso Scale Discovery and Luminex offer enhanced sensitivity and multiplexing capabilities. While mass spectrometry (MS) has been widely used for small molecules and protein detection in the pharmaceutical and agricultural industries (e.g., biomarkers, endogenous allergens), its use in quantifying protein levels in GM crops has been limited. However, as trait portfolios for GM crop have expanded, MS has been increasingly adopted due to its comparable sensitivity, increased specificity, and multiplexing capabilities. This review contrasts the benefits and limitations of immunoassays and MS technologies for protein measurement in GM crops, considering factors such as cost, convenience, and specific analytical needs. Ultimately, both techniques are suitable for assessing protein concentrations in GM crops, with MS offering complementary capabilities to immunoassays. This comparison aims to provide insights into selecting between these techniques based on the user's end point needs.

Measurement of lipid transfer proteins in genetically engineered maize using liquid chromatography with tandem mass spectrometry (LC-MS/MS)

Endogenous allergenicity evaluation is a required part of the risk assessment for genetically engineered (GE) crops. Although maize is not considered a major allergenic food, a lipid transfer protein (Zea m 14) in maize grain has been identified as a potential IgE-mediated food allergen. Currently, the relationship between allergen exposure and risk of sensitization is not well understood. Hence, reliable quantitative methods are useful for determining the natural range and variability of allergen levels across multiple geographies and genetic backgrounds. A LC-MS/MS analytical method was developed and validated in our laboratory to quantify Zea m 14 in grain from 2 GE maize hybrids and 20 non-GE maize hybrids. The measured Zea m 14 levels in GE maize grain and conventional non-GE maize grain ranged from 146.87 to 574.93 ng/mg across 16 field sites located in the United States and Argentina. The method accurately quantified endogenous Zea m 14 from maize grain and results show Zea m 14 levels in the GE maize varieties were within the natural variation observed in traditionally bred non-GE maize.

Analyzing pepsin degradation assay conditions used for allergenicity assessments to ensure that pepsin susceptible and pepsin resistant dietary proteins are distinguishable

The susceptibility of a dietary protein to proteolytic degradation by digestive enzymes, such as gastric pepsin, provides information on the likelihood of systemic exposure to a structurally intact and biologically active macromolecule, thus informing on the safety of proteins for human and animal consumption. Therefore, the purpose of standardized in vitro degradation studies that are performed during protein safety assessments is to distinguish whether proteins of interest are susceptible or resistant to pepsin degradation via a study design that enables study-to-study comparison. Attempting to assess pepsin degradation under a wide-range of possible physiological conditions poses a problem because of the lack of robust and consistent data collected under a large-range of sub-optimal conditions, which undermines the needs to harmonize in vitro degradation conditions. This report systematically compares the effects of pH, incubation time, and pepsin-to-substrate protein ratio on the relative degradation of five dietary proteins: three pepsin susceptible proteins [ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco), horseradish peroxidase (HRP), hemoglobin (Hb)], and two pepsin resistant proteins [lipid transfer protein (LTP) and soybean trypsin inhibitor (STI)]. The results indicate that proteins susceptible to pepsin degradation are readily distinguishable from pepsin-resistant proteins when the reaction conditions are within the well-characterized optima for pepsin. The current standardized in vitro pepsin resistant assay with low pH and high pepsin-to-substrate ratio fits this purpose. Using non-optimal pH and/or pepsin-to-substrate protein ratios resulted in susceptible proteins no longer being reliably degraded by this stomach enzyme, which compromises the ability of this in vitro assay to distinguish between resistant and susceptible proteins and, therefore, no longer providing useful data to an overall weight-of-evidence approach to assessing safety of proteins.