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1.
Pest Manag Sci ; 75(8): 2086-2094, 2019 Aug.
Article in English | MEDLINE | ID: mdl-30828945

ABSTRACT

BACKGROUND: Effective management of weedy species in agricultural fields is essential for maintaining favorable growing conditions and crop yields. The introduction of genetically modified crops containing herbicide tolerance traits has been a successful additional tool available to farmers to better control weeds. However, weed resistance challenges present a need for additional herbicide tolerance trait options. RESULTS: To help meet this challenge, a new trait that provides tolerance to an aryloxyphenoxypropionate (FOP) herbicide and members of the synthetic auxin herbicide family, such as 2,4-dichlorophenoxyacetic acid (2,4-D), was developed. Development of this herbicide tolerance trait employed an enzyme engineered with robust and specific enzymatic activity for these two herbicide families. This engineering effort utilized a microbial-sourced dioxygenase scaffold to generate variants with improved enzymatic parameters. Additional optimization to enhance in-plant stability of the enzyme enabled an efficacious trait that can withstand the higher temperature conditions often found in field environments. CONCLUSION: Optimized herbicide tolerance enzyme variants with enhanced enzymatic and temperature stability parameters enabled robust herbicide tolerance for two herbicide families in transgenic maize and soybeans. This herbicide tolerance trait for FOP and synthetic auxin herbicides such as 2,4-D could be useful in weed management systems, providing additional tools for farmers to control weeds. © 2019 Society of Chemical Industry.


Subject(s)
Glycine max/enzymology , Herbicide Resistance/genetics , Herbicides/pharmacology , Plants, Genetically Modified/enzymology , Zea mays/enzymology , Genetic Engineering , Indoleacetic Acids/pharmacology , Plants, Genetically Modified/genetics , Propionates/pharmacology , Glycine max/genetics , Zea mays/genetics
2.
Regul Toxicol Pharmacol ; 99: 50-60, 2018 Nov.
Article in English | MEDLINE | ID: mdl-30196079

ABSTRACT

The lepidopteran-active Cry1A.105 protein is a chimeric three-domain insecticidal toxin with distinct structural domains derived from the naturally occurring Cry1Ab, Cry1Ac and Cry1F proteins from the soil bacterium Bacillus thuringiensis (Bt). The X-ray crystal structure of the Cry1A.105 tryptic core at 3.0 Šresolution demonstrates its high structural similarity to the tryptic core of Cry1Ac. Bioinformatics analyses demonstrate that Cry1A.105 has no significant amino acid sequence similarity to known allergens or mammalian toxins, which is the same conclusion reached for its component domains. Like its intact donor proteins, Cry1A.105 was heat labile at temperatures ≥75 °C and degraded upon exposure to gastrointestinal proteases. No adverse effects were observed in mice when Cry1A.105 was dosed orally at 2451 mg/kg body weight. Therefore, the weight of evidence supports that Cry1A.105 is safe for human and animal consumption. These results support the conclusion that the safety of a chimeric protein for human or animal consumption can be evaluated in the context of the safety of its donor proteins.


Subject(s)
Bacillus thuringiensis/metabolism , Bacterial Proteins/adverse effects , Amino Acid Sequence , Animals , Endotoxins/adverse effects , Female , Humans , Insecticides/adverse effects , Mice , Recombinant Fusion Proteins/adverse effects
3.
Protein Sci ; 23(11): 1491-7, 2014 Nov.
Article in English | MEDLINE | ID: mdl-25139047

ABSTRACT

For almost half a century, the structure of the full-length Bacillus thuringiensis (Bt) insecticidal protein Cry1Ac has eluded researchers, since Bt-derived crystals were first characterized in 1965. Having finally solved this structure we report intriguing details of the lattice-based interactions between the toxic core of the protein and the protoxin domains. The structure provides concrete evidence for the function of the protoxin as an enhancer of native crystal packing and stability.


Subject(s)
Bacterial Proteins/chemistry , Endotoxins/chemistry , Hemolysin Proteins/chemistry , Insecticides/chemistry , Bacillus thuringiensis Toxins , Models, Molecular , Protein Conformation , Recombinant Proteins/chemistry
4.
Arch Biochem Biophys ; 528(1): 90-101, 2012 Dec 01.
Article in English | MEDLINE | ID: mdl-22750542

ABSTRACT

In this paper we describe the expression, purification, kinetics and biophysical characterization of alanine aminotransferase (AlaAT) from the barley plant (Hordeum vulgare). This dimeric PLP-dependent enzyme is a pivotal element of several key metabolic pathways from nitrogen assimilation to carbon metabolism, and its introduction into transgenic plants results in increased yield. The enzyme exhibits a bi-bi ping-pong reaction mechanism with a K(m) for alanine, 2-oxoglutarate, glutamate and pyruvate of 3.8, 0.3, 0.8 and 0.2 mM, respectively. Barley AlaAT catalyzes the forward (alanine-forming) reaction with a k(cat) of 25.6 s(-1), the reverse (glutamate-forming) reaction with k(cat) of 12.1 s(-1) and an equilibrium constant of ~0.5. The enzyme is also able to utilize aspartate and oxaloacetate with ~10% efficiency as compared to the native substrates, which makes it much more specific than related bacterial/archaeal enzymes (that also have lower K(m) values). We have crystallized barley AlaAT in complex with PLP and l-cycloserine and solved the structure of this complex at 2.7 Å resolution. This is the first example of a plant AlaAT structure, and it reveals a canonical aminotransferase fold similar to structures of the Thermotoga maritima, Pyrococcus furiosus, and human enzymes. This structure bridges our structural understanding of AlaAT mechanism between three kingdoms of life and allows us to shed some light on the specifics of the catalysis performed by these proteins.


Subject(s)
Alanine Transaminase/chemistry , Alanine Transaminase/metabolism , Hordeum/enzymology , Alanine/metabolism , Alanine Transaminase/isolation & purification , Amino Acid Sequence , Aspartic Acid/metabolism , Crystallography, X-Ray , Hordeum/chemistry , Hordeum/metabolism , Humans , Models, Molecular , Molecular Sequence Data , Protein Conformation , Protein Isoforms/chemistry , Protein Isoforms/isolation & purification , Protein Isoforms/metabolism , Sequence Alignment , Substrate Specificity
5.
J Mol Biol ; 392(2): 481-97, 2009 Sep 18.
Article in English | MEDLINE | ID: mdl-19616009

ABSTRACT

Dicamba (2-methoxy-3,6-dichlorobenzoic acid) O-demethylase (DMO) is the terminal Rieske oxygenase of a three-component system that includes a ferredoxin and a reductase. It catalyzes the NADH-dependent oxidative demethylation of the broad leaf herbicide dicamba. DMO represents the first crystal structure of a Rieske non-heme iron oxygenase that performs an exocyclic monooxygenation, incorporating O(2) into a side-chain moiety and not a ring system. The structure reveals a 3-fold symmetric trimer (alpha(3)) in the crystallographic asymmetric unit with similar arrangement of neighboring inter-subunit Rieske domain and non-heme iron site enabling electron transport consistent with other structurally characterized Rieske oxygenases. While the Rieske domain is similar, differences are observed in the catalytic domain, which is smaller in sequence length than those described previously, yet possessing an active-site cavity of larger volume when compared to oxygenases with larger substrates. Consistent with the amphipathic substrate, the active site is designed to interact with both the carboxylate and aromatic ring with both key polar and hydrophobic interactions observed. DMO structures were solved with and without substrate (dicamba), product (3,6-dichlorosalicylic acid), and either cobalt or iron in the non-heme iron site. The substitution of cobalt for iron revealed an uncommon mode of non-heme iron binding trapped by the non-catalytic Co(2+), which, we postulate, may be transiently present in the native enzyme during the catalytic cycle. Thus, we present four DMO structures with resolutions ranging from 1.95 to 2.2 A, which, in sum, provide a snapshot of a dynamic enzyme where metal binding and substrate binding are coupled to observed structural changes in the non-heme iron and catalytic sites.


Subject(s)
Bacterial Proteins/chemistry , Bacterial Proteins/metabolism , Dicamba/metabolism , Mixed Function Oxygenases/chemistry , Mixed Function Oxygenases/metabolism , Stenotrophomonas maltophilia/enzymology , Catalytic Domain , Cobalt/pharmacology , Coenzymes/pharmacology , Crystallography, X-Ray , Models, Molecular , NAD/pharmacology , Protein Multimerization , Protein Structure, Quaternary , Protein Structure, Tertiary
6.
Arch Biochem Biophys ; 480(2): 111-21, 2008 Dec 15.
Article in English | MEDLINE | ID: mdl-18930704

ABSTRACT

The lysine insensitive Corynebacterium glutamicum dihydrodipicolinate synthase enzyme (cDHDPS) was recently successfully introduced into maize plants to enhance the level of lysine in the grain. To better understand lysine insensitivity of the cDHDPS, we expressed, purified, kinetically characterized the protein, and solved its X-ray crystal structure. The cDHDPS enzyme has a fold and overall structure that is highly similar to other DHDPS proteins. A noteworthy feature of the active site is the evidence that the catalytic lysine residue forms a Schiff base adduct with pyruvate. Analyses of the cDHDPS structure in the vicinity of the putative binding site for S-lysine revealed that the allosteric binding site in the Escherichia coli DHDPS protein does not exist in cDHDPS due to three non-conservative amino acids substitutions, and this is likely why cDHDPS is not feedback inhibited by lysine.


Subject(s)
Corynebacterium glutamicum/enzymology , Hydro-Lyases/chemistry , Lysine/chemistry , Amino Acid Sequence , Catalytic Domain , Crystallography, X-Ray/methods , Electrophoresis, Polyacrylamide Gel , Escherichia coli/enzymology , Humans , Inhibitory Concentration 50 , Kinetics , Models, Biological , Molecular Sequence Data , Protein Structure, Tertiary , Sequence Homology, Amino Acid
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