Dataset Information

Desensitizing plant EPSP synthase to glyphosate: Optimized global sequence context accommodates a glycine-to-alanine change in the active site.

ABSTRACT: 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) catalyzes the transfer of a carboxyvinyl group from phosphoenolpyruvate (PEP) to shikimate-3-phosphate and in plants is the target of the herbicide glyphosate. EPSPSs with high catalytic efficiency and insensitivity to glyphosate are of microbial origin, including the enzyme from Agrobacterium strain CP4, in which insensitivity is conferred by an active site alanine. In the sequence context of plant EPSPSs, alanine in place of glycine at the equivalent position interferes with the binding of both glyphosate and PEP. We show here that iterative optimization of maize EPSPS containing the G101A substitution yielded variants on par with CP4 in terms of catalytic activity in the presence of glyphosate. The improvement relative to G101A alone was entirely due to reduction in Km for PEP from 333 to 18 ?m, versus 9.5 ?m for native maize EPSPS. A large portion of the reduction in Km was conferred by two down-sizing substitutions (L97C and V332A) within 8 Å of glyphosate, which together reduced Km for PEP to 43 ?m Although the original optimization was conducted with maize EPSPS, contextually homologous substitutions conferred similar properties to the EPSPSs of other crops. We also discovered a variant having the known glyphosate-desensitizing substitution P106L plus three additional ones that reduced the Km for PEP from 47 ?m, observed with P106L alone, to 10.3 ?m The improvements obtained with both Ala101 and Leu106 have implications regarding glyphosate-tolerant crops and weeds.

SUBMITTER: Dong Y

PROVIDER: S-EPMC6333898 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Publications

Desensitizing plant EPSP synthase to glyphosate: Optimized global sequence context accommodates a glycine-to-alanine change in the active site.

Dong Yuxia Y Ng Emily E Lu Jian J Fenwick Tamara T Tao Yumin Y Bertain Sean S Sandoval Marian M Bermudez Ericka E Hou Zhenglin Z Patten Phil P Lassner Michael M Siehl Daniel D

The Journal of biological chemistry 20181113 2

5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) catalyzes the transfer of a carboxyvinyl group from phosphoenolpyruvate (PEP) to shikimate-3-phosphate and in plants is the target of the herbicide glyphosate. EPSPSs with high catalytic efficiency and insensitivity to glyphosate are of microbial origin, including the enzyme from <i>Agrobacterium</i> strain CP4, in which insensitivity is conferred by an active site alanine. In the sequence context of plant EPSPSs, alanine in place of glycine at ...[more]

PMID: 30425098

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Project description:The epidemiological importance of mycobacterial species is indisputable, and the necessity to find new molecules that can inhibit their growth is urgent. The shikimate pathway, required for the synthesis of important bacterial metabolites, represents a set of targets for inhibitors of Mycobacterium tuberculosis growth. The aroA-encoded 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme catalyzes the sixth step of the shikimate pathway. In this study, we combined gene disruption, gene knockdown, point mutations (D61W, R134A, E321N), and kinetic analysis to evaluate aroA gene essentiality and vulnerability of its protein product, EPSPS, from Mycolicibacterium (Mycobacterium) smegmatis (MsEPSPS). We demonstrate that aroA-deficient cells are auxotrophic for aromatic amino acids (AroAAs) and that the growth impairment observed for aroA-knockdown cells grown on defined medium can be rescued by AroAA supplementation. We also evaluated the essentiality of selected MsEPSPS residues in bacterial cells grown without AroAA supplementation. We found that the catalytic residues R134 and E321 are essential, while D61, presumably important for protein dynamics and suggested to have an indirect role in catalysis, is not essential under the growth conditions evaluated. We have also determined the catalytic efficiencies (Kcat/Km) of recombinant wild-type (WT) and mutated versions of MsEPSPS (D61W, R134A, E321N). Our results suggest that drug development efforts toward EPSPS inhibition may be ineffective if bacilli have access to external sources of AroAAs in the context of infection, which should be evaluated further. In the absence of AroAA supplementation, aroA from M. smegmatis is essential, its essentiality is dependent on MsEPSPS activity, and MsEPSPS is vulnerable. IMPORTANCE We found that cells from Mycobacterium smegmatis, a model organism safer and easier to study than the disease-causing mycobacterial species, when depleted of an enzyme from the shikimate pathway, are auxotrophic for the three aromatic amino acids (AroAAs) that serve as building blocks of cellular proteins: l-tryptophan, l-phenylalanine, and l-tyrosine. That supplementation with only AroAAs is sufficient to rescue viable cells with the shikimate pathway inactivated was unexpected, since this pathway produces an end product, chorismate, that is the starting compound of essential pathways other than the ones that produce AroAAs. The depleted enzyme, the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), catalyzes the sixth step of shikimate pathway. Depletion of this enzyme inside cells was performed by disrupting or silencing the EPSPS-encoding aroA gene. Finally, we evaluated the essentiality of specific residues from EPSPS that are important for its catalytic activity, determined with experiments of enzyme kinetics using recombinant EPSPS mutants.

Dataset Information

Desensitizing plant EPSP synthase to glyphosate: Optimized global sequence context accommodates a glycine-to-alanine change in the active site.

Publications

Desensitizing plant EPSP synthase to glyphosate: Optimized global sequence context accommodates a glycine-to-alanine change in the active site.

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