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  1. Article: Cyanobacterial alkane biosynthesis further expands the catalytic repertoire of the ferritin-like ‘di-iron-carboxylate’ proteins

    Krebs, Carsten / Bollinger, J Martin, Jr / Booker, Squire J

    Current Opinion in Chemical Biology. 2011 Apr., v. 15, no. 2

    2011  

    Abstract: Enzymes that activate dioxygen at carboxylate-bridged non-heme diiron clusters residing within ferritin-like, four-helix-bundle protein architectures have crucial roles in, among other processes, the global carbon cycle (e.g. soluble methane ... ...

    Abstract Enzymes that activate dioxygen at carboxylate-bridged non-heme diiron clusters residing within ferritin-like, four-helix-bundle protein architectures have crucial roles in, among other processes, the global carbon cycle (e.g. soluble methane monooxygenase), fatty acid biosynthesis [plant fatty acyl–acyl carrier protein (ACP) desaturases], DNA biosynthesis [the R2 or β2 subunits of class Ia ribonucleotide reductases (RNRs)], and cellular iron trafficking (ferritins). Classic studies on class Ia RNRs showed long ago how this obligatorily oxidative di-iron/O2 chemistry can be used to activate an enzyme for even a reduction reaction, and more recent investigations of class Ib and Ic RNRs, coupled with earlier studies on dimanganese catalases, have shown that members of this protein family can also incorporate either one or two Mn ions and use them in place of iron for redox catalysis. These two strategies – oxidative activation for non-oxidative reactions and use of alternative metal ions – expand the catalytic repertoire of the family, probably to include activities that remain to be discovered. Indeed, a recent study has suggested that fatty aldehyde decarbonylases (ADs) from cyanobacteria, purported to catalyze a redox-neutral cleavage of a Cn aldehyde to the Cn−1 alkane (or alkene) and CO, also belong to this enzyme family and are most similar in structure to two other members with heterodinuclear (Mn–Fe) cofactors. Here, we first briefly review both the chemical principles underlying the O2-dependent oxidative chemistry of the ‘classical’ di-iron-carboxylate proteins and the two aforementioned strategies that have expanded their functional range, and then consider what metal ion(s) and what chemical mechanism(s) might be employed by the newly discovered cyanobacterial ADs.
    Keywords manganese ; fatty acids ; proteins ; biosynthesis ; catalytic activity ; enzymes ; DNA ; iron ; carbon cycle ; alkanes ; Cyanobacteria ; metal ions
    Language English
    Dates of publication 2011-04
    Size p. 291-303.
    Publishing place Elsevier Ltd
    Document type Article
    Note 2019-12-06
    ZDB-ID 1439176-4
    ISSN 1879-0402 ; 1367-5931
    ISSN (online) 1879-0402
    ISSN 1367-5931
    DOI 10.1016/j.cbpa.2011.02.019
    Database NAL-Catalogue (AGRICOLA)

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  2. Article: Four-electron oxidation of p-hydroxylaminobenzoate to p-nitrobenzoate by a peroxodiferric complex in AurF from Streptomyces thioluteus

    Li, Ning / Korboukh, Victoria Korneeva / Krebs, Carsten / Bollinger, J. Martin Jr

    Proceedings of the National Academy of Sciences of the United States of America. 2010 Sept. 7, v. 107, no. 36

    2010  

    Abstract: The nonheme di-iron oxygenase, AurF, converts p-aminobenzoate (Ar-NH₂, where Ar = 4-carboxyphenyl) to p-nitrobenzoate (Ar-NO₂) in the biosynthesis of the antibiotic, aureothin, by Streptomyces thioluteus. It has been reported that this net six-electron ... ...

    Abstract The nonheme di-iron oxygenase, AurF, converts p-aminobenzoate (Ar-NH₂, where Ar = 4-carboxyphenyl) to p-nitrobenzoate (Ar-NO₂) in the biosynthesis of the antibiotic, aureothin, by Streptomyces thioluteus. It has been reported that this net six-electron oxidation proceeds in three consecutive, two-electron steps, through p-hydroxylaminobenzoate (Ar-NHOH) and p-nitrosobenzoate (Ar-NO) intermediates, with each step requiring one equivalent of O₂ and two exogenous reducing equivalents. We recently demonstrated that a peroxodiiron(III/III) complex (peroxo-Formula -AurF) formed by addition of O₂ to the diiron(II/II) enzyme (Formula -AurF) effects the initial oxidation of Ar-NH₂, generating a μ-(oxo)diiron(III/III) form of the enzyme (μ-oxo-Formula -AurF) and (presumably) Ar-NHOH. Here we show that peroxo-Formula -AurF also oxidizes Ar-NHOH. Unexpectedly, this reaction proceeds through to the Ar-NO₂ final product, a four-electron oxidation, and produces Formula -AurF, with which O₂ can combine to regenerate peroxo-Formula -AurF. Thus, conversion of Ar-NHOH to Ar-NO₂ requires only a single equivalent of O₂ and (starting from Formula -AurF or peroxo-Formula -AurF) is fully catalytic in the absence of exogenous reducing equivalents, by contrast to the published stoichiometry. This novel type of four-electron N-oxidation is likely also to occur in the reaction sequences of nitro-installing di-iron amine oxygenases in the biosyntheses of other natural products.
    Keywords Streptomyces thioluteus ; antibiotics ; biosynthesis ; nitrobenzoic acids ; oxidation ; oxygen ; oxygenases ; stoichiometry
    Language English
    Dates of publication 2010-0907
    Size p. 15722-15727.
    Publishing place National Academy of Sciences
    Document type Article
    ZDB-ID 209104-5
    ISSN 1091-6490 ; 0027-8424
    ISSN (online) 1091-6490
    ISSN 0027-8424
    DOI 10.1073/pnas.1002785107
    Database NAL-Catalogue (AGRICOLA)

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  3. Article: Substrate positioning controls the partition between halogenation and hydroxylation in the aliphatic halogenase, SyrB2

    Matthews, Megan L / Neumann, Christopher S / Miles, Linde A / Grove, Tyler L / Booker, Squire J / Krebs, Carsten / Walsh, Christopher T / Bollinger, J. Martin Jr

    Proceedings of the National Academy of Sciences of the United States of America. 2009 Oct. 20, v. 106, no. 42

    2009  

    Abstract: The α-ketoglutarate-dependent hydroxylases and halogenases employ similar reaction mechanisms involving hydrogen-abstracting Fe(IV)-oxo (ferryl) intermediates. In the halogenases, the carboxylate residue from the His₂(Asp/Glu)₁"facial triad" of iron ...

    Abstract The α-ketoglutarate-dependent hydroxylases and halogenases employ similar reaction mechanisms involving hydrogen-abstracting Fe(IV)-oxo (ferryl) intermediates. In the halogenases, the carboxylate residue from the His₂(Asp/Glu)₁"facial triad" of iron ligands found in the hydroxylases is replaced by alanine, and a halide ion (X⁻) coordinates at the vacated site. Halogenation is thought to result from "rebound" of the halogen radical from the X-Fe(III)-OH intermediate produced by hydrogen (H{bullet}) abstraction to the substrate radical. The alternative decay pathway for the X-Fe(III)-OH intermediate, rebound of the hydroxyl radical to the substrate radical (as occurs in the hydroxylases), reportedly does not compete. Here we show for the halogenase SyrB2 that positioning of the alkyl group of the substrate away from the oxo/hydroxo ligand and closer to the halogen ligand sacrifices H{bullet}-abstraction proficiency for halogen-rebound selectivity. Upon replacement of L-Thr, the C4 amino acid tethered to the SyrB1 carrier protein in the native substrate, by the C5 amino acid L-norvaline, decay of the chloroferryl intermediate becomes 130x faster and the reaction outcome switches to primarily hydroxylation of C5, consistent with projection of the methyl group closer to the oxo/hydroxo by the longer side chain. Competing H{bullet} abstraction from C4 results primarily in chlorination, as occurs at this site in the native substrate. Consequently, deuteration of C5, which slows attack at this site, switches both the regioselectivity from C5 to C4 and the chemoselectivity from hydroxylation to chlorination. Thus, substrate-intermediate disposition and the carboxylate [rightward arrow] halide ligand swap combine to specify the halogenation outcome.
    Keywords alanine ; chlorination ; hydrogen ; hydroxyl radicals ; hydroxylation ; iron ; ligands ; reaction mechanisms
    Language English
    Dates of publication 2009-1020
    Size p. 17723-17728.
    Publishing place National Academy of Sciences
    Document type Article
    ZDB-ID 209104-5
    ISSN 1091-6490 ; 0027-8424
    ISSN (online) 1091-6490
    ISSN 0027-8424
    DOI 10.1073/pnas.0909649106
    Database NAL-Catalogue (AGRICOLA)

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  4. Article: A Manganese(IV)/Iron(III) Cofactor in Chlamydia trachomatis Ribonucleotide Reductase

    Jiang, Wei / Barr, Eric W / Bollinger, J. Martin Jr / Hoffart, Lee M / Krebs, Carsten / Maslak, Monique-Anne / Saleh, Lana / Xing, Gang / Yun, Danny

    Science. 2007 May 25, v. 316, no. 5828

    2007  

    Abstract: In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y{bullet}). The Y{bullet} reversibly oxidizes a ... ...

    Abstract In a conventional class I ribonucleotide reductase (RNR), a diiron(II/II) cofactor in the R2 subunit reacts with oxygen to produce a diiron(III/IV) intermediate, which generates a stable tyrosyl radical (Y{bullet}). The Y{bullet} reversibly oxidizes a cysteine residue in the R1 subunit to a cysteinyl radical (C{bullet}), which abstracts the 3'-hydrogen of the substrate to initiate its reduction. The RNR from Chlamydia trachomatis lacks the Y{bullet}, and it had been proposed that the diiron(III/IV) complex in R2 directly generates the C{bullet} in R1. By enzyme activity measurements and spectroscopic methods, we show that this RNR actually uses a previously unknown stable manganese(IV)/iron(III) cofactor for radical initiation.
    Keywords Chlamydia trachomatis ; cysteine ; enzyme activity ; manganese ; oxygen ; ribonucleotide reductase ; spectroscopy
    Language English
    Dates of publication 2007-0525
    Size p. 1188-1191.
    Publishing place American Association for the Advancement of Science
    Document type Article
    ZDB-ID 128410-1
    ISSN 1095-9203 ; 0036-8075
    ISSN (online) 1095-9203
    ISSN 0036-8075
    DOI 10.1126/science.1141179
    Database NAL-Catalogue (AGRICOLA)

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  5. Article: Four-electron oxidation of p-hydroxylaminobenzoate to p-nitrobenzoate by a peroxodiferric complex in AurF from Streptomyces thioluteus

    Li, Ning / Korboukh, Victoria Korneeva / Krebs, Carsten / Bollinger, J. Martin Jr.
    Language English
    Document type Article
    Database AGRIS - International Information System for the Agricultural Sciences and Technology

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