title: Kinetic dissection of the catalytic mechanism of taurine:alpha-ketoglutarate dioxygenase (TauD) from Escherichia coli.
abstract: Recent studies on taurine:alpha-ketoglutarate dioxygenase (TauD) from Escherichia coli have provided evidence for a three-step, minimal kinetic mechanism involving the quaternary TauD.Fe(II).alpha-ketoglutarate.taurine complex, the taurine-hydroxylating Fe(IV)-oxo intermediate (J) that forms upon reaction of the quaternary complex with O(2), and a poorly defined, Fe(II)-containing intermediate state that converts in the rate-limiting step back to the quaternary complex [Price, J. C., Barr, E. W., Tirupati, B., Bollinger, J. M., Jr., and Krebs, C. (2003) Biochemistry 42, 7497-7508]. The mapping of this kinetic mechanism onto the consensus chemical mechanism for the Fe(II)- and alpha-ketoglutarate-dependent engendered several predictions and additional questions that have been experimentally addressed in the present study. The results demonstrate (1) that postulated intermediates between the quaternary complex and J accumulate very little or not at all; (2) that decarboxylation of alpha-ketoglutarate occurs prior to or concomitantly with formation of J; (3) that the second intermediate state comprises one or more product complex with Mossbauer features that are partially resolved from those of the binary TauD.Fe(II), ternary TauD.Fe(II).alpha-ketoglutarate, and quaternary TauD.Fe(II).alpha-ketoglutarate.taurine complexes; and (4) that the rate-determining step in the catalytic cycle is release of product(s) prior to the rapid, ordered binding of alpha-ketoglutarate and then taurine to regenerate the O(2)-reactive quaternary complex. The results thus integrate the previously proposed kinetic and chemical mechanisms and indicate which of the postulated intermediates in the latter will be detectable only upon perturbation of the kinetics by changes in reaction conditions (e.g., temperature), protein mutagenesis, the use of substrate analogues, or some combination of these.
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Price
authors.forename: Eric W
authors.initials: EW
authors.lastname: Barr
authors.forename: Lee M
authors.initials: LM
authors.lastname: Hoffart
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003653:Decarboxylation; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012997:Solvents / Q000737:chemistry; D015204:Spectroscopy, Mossbauer; D013379:Substrate Specificity; D014783:Viscosity
chemical_list: D029968:Escherichia coli Proteins; D005296:Ferrous Compounds; D007656:Ketoglutaric Acids; D012997:Solvents; D006899:Mixed Function Oxygenases; C433064:taurine-alpha-ketoglutarate dioxygenase; D010100:Oxygen