Publications

• Analysis, cloning, and high-level expression of 2,4-dichlorophenoxyacetate monooxygenase gene tfdA of Alcaligenes eutrophus JMP134.

  Streber W.R., Timmis K.N., Zenk M.H.

  Plasmid pJP4 of Alcaligenes eutrophus JMP134 contains all genes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). Five of these genes, tfdB, tfdC, tfdD, tfdE, and tfdF, have recently been localized and cloned (R. H. Don, A. J. Weightman, H.-J. Knackmuss, and K. N. Timmis, J. Bacteriol ... >> More

  Plasmid pJP4 of Alcaligenes eutrophus JMP134 contains all genes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). Five of these genes, tfdB, tfdC, tfdD, tfdE, and tfdF, have recently been localized and cloned (R. H. Don, A. J. Weightman, H.-J. Knackmuss, and K. N. Timmis, J. Bacteriol. 161:85-90, 1985). Gene tfdA, which codes for the 2,4-D monooxygenase, has now been found by mutagenesis with transposon Tn5. A 3-kilobase fragment of pJP4 cloned in a broad-host-range vector could complement the 2,4-D-negative phenotype of two mutants which lacked 2,4-D monooxygenase activity. The cloned tfdA gene was also transferred to A. eutrophus JMP222, which is a cured derivative of JMP134. The recombinant strain could utilize phenoxyacetic acid as a sole source of carbon and energy. Pseudomonas sp. strain B13, containing the cloned tfdA, was able to degrade phenoxyacetic acid and 4-chlorophenoxyacetic acid. Gene tfdA was subcloned and analyzed by deletions. Expression of 2,4-D monooxygenase in Escherichia coli containing a 1.4-kilobase subfragment was demonstrated by radioisotopic enzyme assay, and a protein of 32,000-dalton molecular mass was detected by labeling experiments. A 2-kilobase subfragment containing tfdA has been sequenced. Sequence analysis revealed an open reading frame of 861 bases which was identified as the coding region of tfdA by insertion mutagenesis. << Less

  J. Bacteriol. 169:2950-2955(1987) [PubMed] [EuropePMC]

• Site-directed mutagenesis of 2,4-dichlorophenoxyacetic acid/alpha-ketoglutarate dioxygenase. Identification of residues involved in metallocenter formation and substrate binding.

  Hogan D.A., Smith S.R., Saari E.A., McCracken J., Hausinger R.P.

  2,4-dichlorophenoxyacetic acid (2,4-D)/alpha-ketoglutarate (alpha-KG) dioxygenase (TfdA) is an Fe(II)-dependent enzyme that catalyzes the first step in degradation of the herbicide 2,4-D. The active site structures of a small number of enzymes within the alpha-KG-dependent dioxygenase superfamily ... >> More

  2,4-dichlorophenoxyacetic acid (2,4-D)/alpha-ketoglutarate (alpha-KG) dioxygenase (TfdA) is an Fe(II)-dependent enzyme that catalyzes the first step in degradation of the herbicide 2,4-D. The active site structures of a small number of enzymes within the alpha-KG-dependent dioxygenase superfamily have been characterized and shown to have a similar HXDX(50-70)HX(10)RXS arrangement of residues that make up the binding sites for Fe(II) and alpha-KG. TfdA does not have obvious homology to the dioxygenases containing the above motif but is related in sequence to eight other enzymes in the superfamily that form a distinct consensus sequence (HX(D/E)X(138-207) HX(10)R/K). Variants of TfdA were created to examine the roles of putative metal-binding residues and the functions of the other seven histidines in this protein. The H167A, H200A, H213A, H245A, and H262A forms of TfdA formed inclusion bodies when overproduced in Escherichia coli DH5alpha; however, these proteins were soluble when fused to the maltose-binding protein (MBP). MBP-TfdA exhibited kinetic parameters similar to the native enzyme. The H8A and H235A variants were catalytically similar to wild-type TfdA. MBP-H213A and H216A TfdA have elevated K(m) values for 2,4-D, and the former showed a decreased k(cat), suggesting these residues may affect substrate binding or catalysis. The H113A, D115A, MBP-H167A, MBP-H200A, MBP-H245A and MBP-H262A variants of TfdA were inactive. Gel filtration analysis revealed that the latter two proteins were highly aggregated. The remaining four inactive variants were examined in their Cu(II)-substituted forms by EPR and electron spin-echo envelope modulation (ESEEM) spectroscopic methods. Changes in EPR spectra upon addition of substrates indicated that copper was present at the active site in the H113A and D115A variants. ESEEM analysis revealed that two histidines are bound equatorially to the copper in the D115A and MBP-H167A TfdA variants. The experimental data and sequence analysis lead us to conclude that His-113, Asp-115, and His-262 are likely metal ligands in TfdA and that His-213 may aid in catalysis or binding of 2,4-D. << Less

  J. Biol. Chem. 275:12400-12409(2000) [PubMed] [EuropePMC]