Barry W. Schafer

Photorhabdus luminescens W-14 Insecticidal Activity Consists of at Least Two Similar but Distinct Proteins PURIFICATION AND CHARACTERIZATION OF TOXIN A AND TOXIN B

Both the bacterium Photorhabdus luminescens alone and its symbioticPhotorhabdus-nematode complex are known to be highly pathogenic to insects. The nature of the insecticidal activity ofPhotorhabdus bacteria was investigated for its potential application as an insect control agent. It was found that in the fermentation broth of P. luminescens strain W-14, at least two proteins, toxin A and toxin B, independently contributed to the oral insecticidal activity against Southern corn rootworm. Purified toxin A and toxin B exhibited single bands on native polyacrylamide gel electrophoresis and two peptides of 208 and 63 kDa on SDS-polyacrylamide gel electrophoresis. The native molecular weight of both the toxin A and toxin B was determined to be approximately 860 kDa, suggesting that they are tetrameric. NH2-terminal amino acid sequencing and Western analysis using monospecific antibodies to each toxin demonstrated that the two toxins were distinct but homologous. The oral potency (LD50) of toxin A and toxin B against Southern corn rootworm larvae was determined to be similar to that observed with highly potent Bt toxins against lepidopteran pests. In addition, it was found that the two peptides present in toxin B could be processed in vitro from a 281-kDa protoxin by endogenous P. luminescens proteases. Proteolytic processing was shown to enhance insecticidal activity.

Stability of a set of allergens and non-allergens in simulated gastric fluid

Stability in simulated gastric fluid has been suggested as a parameter for consideration in the allergenicity assessment of transgenic proteins. However, the relationship between the stability of proteins in simulated gastric fluid and allergenicity has been inconsistent among studies conducted with reference allergens and non-allergens. Differences in laboratory methods and data interpretation have been implicated as possible causes for conflicting study results. We attempted to mitigate some of the methodological inconsistencies among laboratory methods by applying a kinetic interpretation to results of digestion experiments conducted with a set of known allergens and putative non-allergens. We found that pepsinolysis in simulated gastric fluid generally followed an exponential (pseudo-first-order) pattern of decay, at least during the terminal (slower) phase of digestion, allowing the calculation of digestion half-lives. While digestibility estimates were reproducible and robust, results for the proteins evaluated in this study did not support a significant association between stability in simulated gastric fluid and allergenicity.

Quantification and characterization of maize lipid transfer protein, a food allergen, by liquid chromatography with ultraviolet and mass spectrometric detection.

Maize (Zea mays) is not considered a major allergenic food; however, when food induced allergenic and immunologic reactions have been implicated to maize, lipid transfer proteins (LTPs) have been identified as major allergens. LTP is an extremely stable protein that is resistant to both proteolytic attack and food processing, which permits the allergen to reach the gastrointestinal immune system in an immunogenic and allergenic conformation, allowing sensitization and induction of systemic symptoms. They are considered a complete food allergen in that they are capable of inducing specific IgE as well as eliciting severe symptoms. We have purified and characterized an endogenous ~9 kDa LTP from maize kernels. The maize LTP consists of 93 amino acid residues and has a M(r) of 9046.1 Da, determined by electrospray ionization mass spectrometry. Following accurate identification and characterization of maize LTP, a highly specific and quantitative assay using liquid chromatography with ultraviolet and mass spectrometric detection was developed. The present assay enables determination of LTP over a concentration range from 29 to 1030 μg/g in maize kernel samples. Assay recovery (percent relative error, % RE) was measured at 11 different concentrations ranging from 4 to 147 μg/mL and did not exceed 5.1%. The precision (percent coefficient of variation, % CV) was measured at 3 concentrations on each of 4 days and did not exceed 14.4%. The method was applied to evaluate the levels of LTP in 14 different maize lines. To our knowledge, this represents the first quantitative liquid chromatography-ultraviolet/mass spectrometry (LC-UV/MS) assay for the determination of LTP for the assessment of a food allergen.

Characterization of Cry34Ab1 and Cry35Ab1 insecticidal crystal proteins expressed in transgenic corn plants and Pseudomonas fluorescens

Cry34Ab1 and Cry35Ab1 proteins, identified from Bacillus thuringiensis strain PS149B1, act together to control corn rootworms. Transgenic corn lines coexpressing the two proteins were developed to protect corn against rootworm damage. Large quantities of the two proteins were needed to conduct studies required for assessing the safety of this transgenic corn crop. Because it was technically infeasible to obtain sufficient quantities of high purity Cry34Ab1 and Cry35Ab1 proteins from the transgenic corn plants, the proteins were produced using a recombinant Pseudomonas fluorescens (Pf) production system. The two proteins from both the transgenic corn and the Pf were purified and characterized. The proteins from each host had the expected molecular mass and were immunoreactive to specific antibodies in enzyme-linked immunosorbent assay and Western blot analysis. Data from N-terminal sequencing, tryptic peptide mass fingerprinting, internal peptide sequencing, and biological activity provided direct evidence that the Cry34Ab1 and Cry35Ab1 proteins produced in Pf and transgenic corn were, respectively, comparable or equivalent molecules. In addition, neither protein had detectable glycosylation regardless of the host.

Quantification of Gly m 4 protein, a major soybean allergen, by two-dimensional liquid chromatography with ultraviolet and mass spectrometry detection.

Soybean (Glycine max) is considered a major allergenic food. Gly m 4 is one of several soybean allergens that has been identified to cause an allergic reaction, typically the symptoms are localized effects including the skin, gastrointestinal tract, or respiratory tract. Soybean allergens are considered a complete food allergen in that they are capable of inducing specific IgE as well as eliciting a range of severity from mild rashes up to anaphylaxis. In this study, we have isolated, purified, and characterized an endogenous Gly m 4 protein. The endogenous protein has 88.0% sequence homology with the theoretically predicted Gly m 4 sequence. Following detailed characterization, an assay was developed for quantification of endogenous Gly m 4 using two-dimensional liquid chromatography with ultraviolet and mass spectrometric detection (2DLC-UV/MS). A linear relationship (R(2) > 0.99) was observed over the concentration range of 12.5-531.7 μg/mL. Over the linear range, the assay recoveries (percent relative error, % RE) ranged from -1.5 to 10.8%. The assay precision (percent coefficient of variation, % CV) was measured at three different Gly m 4 levels on each of the 4 days and did not exceed 11.2%. The developed method was successfully applied to quantify Gly m 4 level in 10 commercial soybean lines. To the best of our knowledge, this represents the first quantitative assay for an intact endogenous Gly m 4 protein.

Stacking transgenic event DAS-Ø15Ø7-1 alters maize composition less than traditional breeding

Summary The impact of crossing (‘stacking’) genetically modified (GM) events on maize‐grain biochemical composition was compared with the impact of generating nonGM hybrids. The compositional similarity of seven GM stacks containing event DAS‐Ø15Ø7‐1, and their matched nonGM near‐isogenic hybrids (iso‐hybrids) was compared with the compositional similarity of concurrently grown nonGM hybrids and these same iso‐hybrids. Scatter plots were used to visualize comparisons among hybrids and a coefficient of identity (per cent of variation explained by line of identity) was calculated to quantify the relationships within analyte profiles. The composition of GM breeding stacks was more similar to the composition of iso‐hybrids than was the composition of nonGM hybrids. NonGM breeding more strongly influenced crop composition than did transgenesis or stacking of GM events. These findings call into question the value of uniquely requiring composition studies for GM crops, especially for breeding stacks composed of GM events previously found to be compositionally normal.

Characterization of Aryloxyalkanoate Dioxygenase-12, a Nonheme Fe(II)/α-Ketoglutarate-Dependent Dioxygenase, Expressed in Transgenic Soybean and Pseudomonas fluorescens

Aryloxyalkanoate dioxygenase-12 (AAD-12) was discovered from the soil bacterium Delftia acidovorans MC1 and is a nonheme Fe(II)/α-ketoglutarate-dependent dioxygenase, which can impart herbicide tolerance to transgenic plants by catalyzing the degradation of certain phenoxyacetate, pyridyloxyacetate, and aryloxyphenoxypropionate herbicides. (1) The development of commercial herbicide-tolerant crops, in particular AAD-12-containing soybean, has prompted the need for large quantities of the enzyme for safety testing. To accomplish this, the enzyme was produced in Pseudomonas fluorescens (Pf) and purified to near homogeneity. A small amount of AAD-12 was partially purified from transgenic soybean and through various analytical, biochemical, and in vitro activity analyses demonstrated to be equivalent to the Pf-generated enzyme. Furthermore, results from in vitro kinetic analyses using a variety of plant endogenous compounds revealed activity with trans-cinnamate and indole-3-acetic acid (IAA). The catalytic efficiencies (kcat/Km) of AAD-12 using trans-cinnamate (51.5 M(-1) s(-1)) and IAA (8.2 M(-1) s(-1)) as substrates were very poor when compared to the efficiencies of plant endogenous enzymes. The results suggest that the presence of AAD-12 in transgenic soybean would not likely have an impact on major plant metabolic pathways.

Preliminary safety assessment of a membrane-bound delta 9 desaturase candidate protein for transgenic oilseed crops.

A gene encoding delta 9 desaturase (D9DS), an integral membrane protein, is being considered for incorporation into oilseed crops to reduce saturated fatty acids and thus improve human nutritional value. Typically, a safety assessment for transgenic crops involves purifying heterologously produced transgenic proteins in an active form for use in safety studies. Membrane-bound proteins have been very difficult to isolate in an active form due to their inherent physicochemical properties. Described here are methods used to derive enriched preparations of the active D9DS protein for use in early stage safety studies. Results of these studies, in combination with bioinformatic results and knowledge of the mode of action of the protein, along with a history of safe consumption of related proteins, provides a weight of evidence supporting the safety of the D9DS protein in food and feed.

Development, Validation, and Interlaboratory Evaluation of a Quantitative Multiplexing Method To Assess Levels of Ten Endogenous Allergens in Soybean Seed and Its Application to Field Trials Spanning Three Growing Seasons

As part of the regulatory approval process in Europe, comparison of endogenous soybean allergen levels between genetically engineered (GE) and non-GE plants has been requested. A quantitative multiplex analytical method using tandem mass spectrometry was developed and validated to measure 10 potential soybean allergens from soybean seed. The analytical method was implemented at six laboratories to demonstrate the robustness of the method and further applied to three soybean field studies across multiple growing seasons (including 21 non-GE soybean varieties) to assess the natural variation of allergen levels. The results show environmental factors contribute more than genetic factors to the large variation in allergen abundance (2- to 50-fold between environmental replicates) as well as a large contribution of Gly m 5 and Gly m 6 to the total allergen profile, calling into question the scientific rational for measurement of endogenous allergen levels between GE and non-GE varieties in the safety assessment.

Rapid simulated gastric fluid digestion of in-seed/grain proteins expressed in genetically engineered crops.

The speed of simulated gastric digestion of proteins expressed in genetically engineered (GE) crops is commonly used to inform the allergenicity risk assessment. However, persistence of purified proteins in simulated gastric fluid (SGF) is poorly correlated with the allergenic status of proteins. It has been proposed that the plant or food matrix may affect the digestion of proteins and should be considered in interpreting digestion results. Here the SGF digestion of several GE proteins both as purified preparations and in soybean, corn, and cotton seed/grain extracts (in-matrix) are compared. Cry1F, Cry1Ac, phosphinothricin acetyltransferase (PAT), aryloxyalkanoate dioxygenase-1 (AAD-1), aryloxyalkanoate dioxygenase-12 (AAD-12), and double mutant 5-enol pyruvylshikimate-3-phosphate synthase (2mEPSPS) were all found to rapidly digest both as purified protein preparations and in seed/grain extracts from GE crops expressing these proteins. Based on these results, purified protein from microbial sources is a suitable surrogate for proteins in-matrix when conducting SGF digestion studies.